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A short review on hydrogen, bio-fuel and electricity production using seawater as a medium Kumaravel Vignesh, and Ahmed Abdel-Wahab Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b00995 • Publication Date (Web): 22 May 2018 Downloaded from http://pubs.acs.org on May 22, 2018
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Energy & Fuels
Contents: 1. Introduction 2. Technologies available for energy production/conversion using seawater 2.1. Hydrogen generation 2.1.1. Photo-catalysis 2.1.2. Photo-electrochemical 2.1.3. Bio-chemical 2.2. Biofuel production 2.3. Seawater batteries 2.4. Electricity generation 2.4.1. Microbial desalination cells (MDC) 2.4.2. Salinity Gradient Energy Pressure-retarded osmosis (PRO) Reverse electro-dialysis (RED) Capacitive mixing (CAPMIX) Mixing entropy battery (MEB) 3. Summary Acknowledgement References
1. Introduction: In the 21st century, energy security and control of global warming are the two important challenges worldwide. Nearly 80-85 % of the world’s energy demand is obtained from the nonrenewable fossil fuels such as oil, coal and natural gas 1. The consumption of fossil fuels has been doubled every two decades
2, 3
. Moreover, the emission of greenhouse gases from fossil
fuels is the major cause for global warming. Therefore, harvesting energy from renewable sources is a mandate to devoid the effects of greenhouse gas pollution. At present, only 15-20 % of energy is produced from the renewable sources such as solar, wind, tidal, biomass, geothermal and hydropower 1. Governments and funding agencies allot a major portion of resources towards energy production via cost effective and environmental benign technologies to secure the energy supply for the future generation. Most of the renewable energy technologies have the following 2 ACS Paragon Plus Environment
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constraints: sources are located in remote area, not always available, limited commercialization potential and more expensive to produce compared to conventional energy sources. Seawater is the most earth-abundant natural resource (more than 90 % of earth’s water source). From the practical point of view, conversion/production of energy using seawater would be highly desirable. NaCl, MgCl2, MgSO4, CaSO4, K2SO4, K2CO3 and MgBr2 are the important contents of natural seawater. Among them NaCl (~3.5 %) is the major constituent for the salinity of seawater (salinity percentage: Chloride 55 % and Sodium 30 %). Several technologies have been investigated for extracting energy from it (Fig. 1). The percentages of articles that have been published to date on each technology are shown in Fig. 2 (the percentages have been estimated on the basis of the number of research articles reviewed in in each section). It can be observed that bio-chemical processes for the production of hydrogen or electricity have attracted considerable attention. The following sections discuss the technologies that have been evaluated for energy production using seawater.
Fig. 1. Various technologies used to produce energy using seawater
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Fig. 2. The contribution of research publications on energy production using seawater 2. Technologies available for energy production from seawater 2.1. Hydrogen Production: 2.1.1.Photocatalysis: Photocatalytic water splitting has been identified as a promising technology for H2 production 4. When a semiconductor is irradiated with light energy equivalent to or higher than the band gap energy, electrons are excited from the valence band (VB) to the conduction band (CB), and therefore electron-hole pairs are formed (Fig. 3). Holes (h+) in the VB can oxidize the water into oxygen (O2). Electrons (e-) in the CB can reduce the hydrogen (H+) ions into molecular hydrogen (H2). To attain this oxidation–reduction reaction, the CB minimum potential of a photo-catalyst must be lower than the reduction potential of H+/H2 (0 V vs. NHE) and the VB maximum potential must be higher than the oxidation potential of H2O/O2 (+1.23 V vs. NHE), respectively. The photocatalytic water splitting is an uphill reaction and hence the experiments are generally performed in the presence of hole scavenging agents such as ethanol, methanol, triethanolamine and sodium sulfide/sodium sulfite mixture 4-7. Titanium dioxide (TiO2) and zinc oxide (ZnO) are the most commonly preferred photocatalysts
4, 8-13
. However, their wide band gap energy allows only a small portion of solar
spectrum (only UV light) to be utilized. Therefore, there have been appreciable amount of research work on developing visible light responsive photo-catalysts via doping with metals 14, 15,
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decorating with dyes
16, 17
, coupling with narrow band gap semiconductors
Page 4 of 38
18, 19
, Z-Scheme
systems 20, and constructing hetero-structures 21, 22. Moreover, H2 generation is also promoted by the existence of a solid co-catalyst (like noble metals (Ag, Pt, Pd, Rh.), metal oxides (NiO, RuO2)) via the formation of more active sites and minimizing the activation energy 19.
Fig. 3. Schematic representation of H2 production via photo-catalytic water splitting Most of the studies in this area are focused on using precious pure water. The studies regarding the utilization of natural or synthetic seawater for H2 production are very limited. The results are summarized in Table 1. In many cases, the H2 production efficiency of photocatalyst in natural seawater medium is higher than the synthetic seawater. The surface characteristics (surface area, co-catalyst, defects, light absorption capacity, and morphology) of the photocatalyst, NaCl concentration of seawater and concentration of sacrificial agent are the important parameters that influence the H2 production efficiency. The photo-generated electrons and holes have very short life time. If the hole scavenging action of sacrificial agent is poor, the electron and hole will recombine again, it will influence the H2 production efficiency of the photocatalyst. To attain the maximum electron-hole separation process, the sacrificial agent should be effectively adsorbed on the photocatalyst surface for its reaction with photo-generated holes. The NaCl content of seawater can support the adsorption of sacrificial agents on the photo-catalyst surface. Na+ ions tend to attach the sacrificial agents via ionic bond or electrostatic interaction. 5 ACS Paragon Plus Environment
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Therefore, the seawater medium promotes the hole scavenging action of sacrificial agents and improves the electron-hole separation on the photocatalyst surface NaCl content to achieve maximum efficiency
24
23
. 3.5 % was the optimum
. The photocatalytic activity was decreased at
high salinity. In addition to that, most of the photocatalysts are chemically stable in the seawater medium under prolonged light irradiation. Ji et al. 24 evaluated the effect of different metal salts on the H2 production efficiency. They found that the efficiency was dropped significantly in the presence of MgCl2 and it was high in the presence of K2SO4 when compared to other salts. Therefore, the removal of Mg ions from seawater could further improve the photocatalytic efficiency. Gao et al. 25 investigated the formation of oxidized chloride compounds (e.g., Cl2 gas, hypochlorite, alkyl halides) during the photo-catalytic seawater splitting reaction. It was observed that the chloride content was not changed throughout the photochemical reaction. This is ascribed to chloride radicals are reduced back to chloride ions by photo-electrons. Table.1. Summary of the efficiency of different photocatalysts for H2 production using seawater
Photocatalyst
Water source
Activation
Sacrificial
method
agent
Comments
ZnS1-x-
Synthetic
Visible light
0.10 mol L-1
Catalyst synthesized
0.5yOx(OH)y-
seawater
(400 W Hg
Na2S and
by hydrothermal
with UV
0.040 mol
method showed very
cutoff filter)
L-1 Na2SO3
good performance.
ZnO/NiS (1 %)
Reference
22
The efficiency of catalyst in seawater is higher than in pure water. TiO2
Natural seawater
Sun light
Cyclohexen
H2 production rate
e (5 %)
for seawater is
26
higher than that of pure water Pt/Cd0.5Zn0.5S
Synthetic
Visible light
seawater
(400 W Hg
Glucose
H2 production rate increases with
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with UV
increase of NaCl
cutoff filter)
concentration upto 3 mol/L. The efficiency for seawater is higher than that of pure water.
Rutile TiO2
Pure water and
UV light (500
-
H2, H2O2 and O2 are
synthetic
W Xe) +
identified as
seawater
Sonication
products.
(4 %, 10 %, 20
(200 KHz)
Sono-photocatalytic
% and 25 %
efficiency decreases
NaCl)
with increase of
27
NaCl concentration. The efficiency of pure water system is higher than that of seawater. La2Ti2O7
Pure water (PW), UV light (400
Na2S and
Efficiency of
(for UV light)
natural seawater
Na2SO3
La2Ti2O7 :
CdS/TiO2
(NSW), and
(for visible
synthetic
light)
seawater (SSW)
W Hg)
24
PW > NSW > SSW
Efficiency of CdS/TiO2: SSW > NSW > PW
TiO2/CuO (2.5
Synthetic
UV-Vis light
%)
seawater (3.5 %
(300 W Xe)
-
H2 production efficiency of pure
NaCl)
water is higher than that of seawater. The activity of TiO2/CuO (2.5 %) is 7 ACS Paragon Plus Environment
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7.8 times higher than TiO2 in seawater splitting. CuO/TNT
Synthetic
UV light (300
0.05 Oxalic
The efficiency of
seawater (3.5 %
W Xe)
acid
CuO/TNT is much
NaCl)
29
higher than that of TNT.
a)TiO2/CuO
Synthetic
UV-Vis light
0.05 M
H2 production
b)TiO2/NiO
seawater (3.5 %
(300 W Xe)
oxalic acid
efficiency of pure
30
water is higher than
NaCl)
seawater. CuO/nanoTiO2 showed better efficiency when compared to NiO/nano-TiO2. Ladder type
Synthetic
Simulated
WO2-NaxWO3
seawater (pH
solar light
of 37.5% WO2 and
6.5)
(1000 W Xe)
62.5% NaxWO3
+ IR light
showed maximum
(980 nm laser)
efficiency.
-
Catalyst composed
31
The photocatalytic activity is maintained well for 90 h. SiO2/Ag@TiO2 Synthetic
Visible light
20 % v/v
The nano-composite
core-shell
seawater (3. 5 %
(300 W Xe
glycerol
has photocatalytic,
(solar thermal
NaCl)
with UV
plasmonic and
cutoff filter)
photothermic
collector nanocomposite)
attributes. H2 generation efficiency: 8 ACS Paragon Plus Environment
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SiO2/Ag@TiO2 > SiO2@TiO2 > TiO2 . H2 production rate for seawater is lower than that of pure water. ZnS1-x-
Synthetic
Visible light
0.10 mol/L
The activity is
0.5yOx(OH)y-
seawater
(400 W Hg
Na2S and
strongly influenced
with UV cut-
0.040 mol/L
by the NaCl content.
off filter)
Na2SO3
When the NaCl
ZnO
32
concentration is high (3 mol/L), the efficiency of the catalyst in seawater is higher than in pure water Ni-ZnO@C
Synthetic
UV-Vis light
CH3OH
Catalyst with Zn/Ni
nanoreactor
seawater
(300 W Xe )
(2 %)
mole ratio of 1
(3.5 % NaCl)
33
showed maximum efficiency.
2.1.2.Photo-electrochemical (PEC): PEC is one of the most promising technologies for H2 production via electrolysis of water under light irradiation. The photocatalyst is deposited as a thin film on a suitable substrate to form a photo-anode or photo-cathode. During light irradiation electron-hole pairs are generated in the photo-electrode, which can participate in the redox reactions at the electrode/water (electrolyte) interface. Photon with energy sufficient to generate above 1.23 V is required for H2 production. An external circuit is also required to direct the photo-generated electrons. The schematic representation of a PEC cell is shown in Fig. 4 34. 9 ACS Paragon Plus Environment
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Fig. 4. Schematic representation of a PEC cell
34
The reactions occur in a PEC system is given as follows 34: Photo-electrode + hυ
e- + h+
(1)
H2O + ½ O2 (g)
(2)
2OH- + H2 (g)
(3)
H2 (g) + ½ O2 (g)
(4)
Oxygen evolution reaction (OER): 2OH- + 2h+ Hydrogen evolution reaction (HER): 2H2O + 2eOverall reaction: H2O + hυ
Photo-anodes with n-type semiconductors favor OER; photo-cathodes with p-type semiconductors promote HER. PEC experiments are usually carried out in a three-electrode system using platinum wire, Ag/AgCl and photo-catalyst as the counter, reference, and working electrodes, respectively. PEC performance was evaluated in terms of current density by measuring the linear sweep voltammetry (LSV) curves. Most of the highly efficient photo-electrodes are tested in an acidic electrolyte using pure water. Seawater is a naturally available electrolyte and it has high quantities of dissolved ions when compared to pure water. In 1997, Ichikawa
35
successfully utilized natural seawater as an
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electrolyte solution for the first time to produce H2 under sunlight irradiation. The results of this work encouraged other researchers to study the PEC performance using natural seawater electrolyte. Recently Li et al.
36-38
evaluated the PEC performance of WO3/g-C3N4, TiO2@g-
C3N4/Co-Pi and α-Fe2O3/WO3 nano-rod arrays using natural seawater. The main findings of their work are summarized in Table 2. The efficiency and stability of the nano-composites were found to be higher than that of bare metal oxides. This was attributed to maximum visible absorption and effective charge separation. These results also proved that the photoelectrodes are stable under prolonged light irradiation for PEC seawater splitting. The efficiency of natural seawater electrolyte is almost the same to pure water with Na2SO4 or K2SO4. Table 2. PEC performance of nano-rod arrays in seawater electrolyte Photo-anode
2D WO3/g-C3N4
LSV
Scan Current
rate
density
(mV s-1 )
(mA/cm2)
5
0.73
Comments
Reference
The efficiency of nano-
36
composite is higher than that of WO3. The photoanode is stable after 1 h of continuous light irradiation TiO2@g-C3N4 /Co-Pi
10
1.6
The performance of photo-
37
anode is not changed after 10 h of continuous light irradiation α-Fe2O3/WO3
10
1
The efficiency of nanocomposite
is
50
times
higher than that of Fe2O3. However, 35 % of current density is dropped after 5 h of
continuous
irradiation
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light
38
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Nam et al. 39-42 evaluated PEC performance of TiO2 photo-anodes using natural seawater. H2 evolution rate of TiO2 photo-anode was ca. 215 µmol/cm2 h at an optimum external bias of 3.0 V. The efficiency was further increased by the deposition of Pt (0.2 wt %) co-catalyst
40
or
42
enzyme . Nam et al. suggested that nano-composite showed high performance when compared to single-phase electrode. The performance was further improved in concentrated seawater electrolyte
41
because, seawater with high total dissolved salts (TDS) favor the rapid ionic
transport across the electrode/electrolyte interface. This also offers the potential of using seawater brine from desalination plant as an electrolyte solution for PEC.
2.1.5. Bio-chemical: Seawater contains a lot of natural organic matter. Micro-organisms such as cyanobacteria, phototrophic bacteria and dark-acidogenic bacteria have the ability to produce H2 via fermentation of organic matter in seawater. These micro-organisms can break down the organic matter into H2 and volatile fatty acids (VFA)
43-46
. Among them, phototropic bacteria
have the only ability to further degrade the VFA into H2 and CO2 47. The fermentation reactions are carried out in the presence of essential nutrients related to the specific micro-organism. Microbial growth and H2 production require slight alkaline pH
47
. Hence, seawater is a more
attractive medium when compared to pure water. Table 3 summarizes the H2 production efficiency of different marine micro-organisms in seawater.
Table 3. Summary of H2 production efficiency of marine micro-organism in seawater Micro-
Water
organism
source
Phototrophic
Natural
bacterial consort seawater, China
Condition
Nutrient
Phototrophic Butyrate
Comments
Reference
Maximum
H2
and
production is achieved
sodium
at 30 °C, light intensity
glutamate
of
80
mmol
photons/m2s, and pH 8. The
yield
of
H2
production is decreased with 12 ACS Paragon Plus Environment
increase
of
47
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butyrate concentration. Cyanobacterium Natural
Dark
(Aphanothece
seawater, anaerobic
halophytica)
Thailand
NaNO3,
H2 production rate is
glucose,
higher
fermentation Ni2+
for
the
48
cells
and incubated in seawater
Fe3+ salts
without
NaNO3.
The
efficiency is influenced by NaCl, glucose, Ni2+ and Fe3+ concentration. Macroalgae
Natural
Dark
DSMZ
H2 production rate is
Sargassum sp
seawater, fermentation medium
influenced by inoculum
Portugal
concentration.
and
and
anaerobic
Cellobiose with 14-20% of H2 was
digestion
49
Bio-gas
produced.
Operating conditions such as pH, temperature and light intensity, availability of nutrients and nature of marine bacterial strains are important factors that determine the H2 production efficiency. Among them, pH and incubation temperature are the main influencing factors
47
.
Addition of some extra nutrients into seawater could further enhance the H2 production efficiency.
2.4. Bio-fuel production using seawater: Methane: Methane (CH4) gas can be produced from the anaerobic microbial conversion of marine microalgae
50
in seawater. However, the high concentration of sodium ions (Na+) is toxic to the
microbial communities (especially methanogens). Hence, marine sediments are used as salt tolerant microbial source to produce CH4 using seawater and microalgae. Three major steps are involved in the biomass conversion: (1) Formation of volatile fatty acids (VFA) by various bacteria; (2) Transformation of VFA into acetate and hydrogen by propionate and butyrate oxidizing bacteria, respectively; (3) Conversion of acetate into CH4 and CO2 by acetoclastic methanogens and conversion of H2 and CO2 into CH4 by hydrogenotrophic methanogens. The
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yield of CH4 highly depends on the activity of these three steps. Table 4 summarizes the yield of CH4 production using various microalgae and marine sediments in seawater. Table 4. Summary of CH4 production using marine sediments and seawater Algae
Seawater
Marine sediment Comments
Reference
(MS) Saccharina
Synthetic seawater Tokoyo
bay, MS showed high
japonica
(30 g/L NaCl)
Hiroshima
bay, butyrate
and
sea, acetate
Ariake
Japan
and
conversion when to
51
rates
compared mesophilic
methanogenic granules. Sea
wrack Natural seawater
biomass
Mangrove and sea grass
High CH4 yield
52
mudflat, was achieved by
Philippines
MS
when
compared to cow manure and sea wrack associated microflora Macrocystis pyrifera
Natural seawater
Jiaozhou China
Bay,
High CH4 yield
(Littoral) was achieved by
and Arabian Sea the (Sub-littoral)
when to
littoral
MS
compared sub-littoral
MS.
CH4
formation
was
achieved
via
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syntrophic acetate oxidation coupled with
hydroge-
notrophic methanogenesis.
The results reveal that microbial process and CH4 yield are strongly influenced by the nature of marine sediments. The efficiency was also affected by the change in physico-chemical parameters such as pH, temperature and salinity. CH4 was not formed in the initial days of microbial process, instead H2S and CO2 was detected. This was attributed to the existence of sulfate and sulfate-reducing bacteria (SRB) in seawater
53
. This could be rectified by the
application of specific SRB inhibitors. Fan et al. found that CH4 production was improved in the presence of 0.8 mM sodium molybdate as SRB inhibitor
53
. They also found that littoral
sediments showed high methanogenetic activity when compared to sub-littoral sediments. The difference in utilizing acetate by the marine sediments might be the reason for the variation in CH4 yield because acetate is considered as the general precursor in the anaerobic microbial production of CH4.
Biodiesel: The most significant steps of bio-diesel production from microalgae are lipid synthesis (e.g., triglycerides (TAG)), lipid extraction and its conversion to biodiesel
54, 55
. Nutrients are
very essential for the bio-synthesis of chlorophyll, DNA, RNA and protein. Significant amount of water and large area of land are required for the production of bio-diesel via conventional plant cultivation method
56
. Therefore, the utilization of seawater as a microalgal cultivation
media is greatly desirable to conserve the land and fresh water resources. Moreover, the use of seawater reduces the amount of mineral supplementation. The microbial process is mainly governed by the composition of nutrients and salinity of the cultivation medium. Depending on the nature of microalgae, the cultivation is carried out in two ways: phototrophic (requires light and organic carbon source) and heterotrophic (requires only organic carbon source). The following steps are involved in the biodiesel production: 1) algal strain isolation; 2) cultivation in the presence of carbon (C), nitrogen (N), and phosphorus (P) nutrients; 3) harvesting; 4) drying; 15 ACS Paragon Plus Environment
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Energy & Fuels
5) lipid extraction and 6) trans-esterification. Among these, strain selection is very important for the cost effective bio-diesel production. Strains that have the ability to grow under local climatic conditions are beneficial for economic success and environmental sustainability. Table 5 summarizes the yield of bio-diesel production using different micro-algae in seawater.
Table 5. Summary of bio-diesel production using marine microalgae and seawater Algae
Seawater
Growth
Fatty
acid Lipid
condition
carbon chain
Reference
yield (mg
L−1
day−1)
Nannochloropsis Natural
Phototrophic
-
13.70
57
58
gaditana Q6
seawater
Chlorococcum
Natural
Phototrophic
polyunsaturated
3.31
sp. RAP13
seawater
Heterotrophic
medium
20.33
(glucose)
saturated
chain and
monounsaturated Heterotrophic,
Medium
(glycerol waste)
saturated
chain and 22
monounsaturated Neochloris
Natural
Phototrophic
oleoabundans
seawater
(N-stress)
Tetraselmis sp.
Natural
Phototrophic
seawater Nannochloropsis Synthetic gaditana
56
59
Unsaturated and 16
60
monounsaturated
monounsaturated Phototrophic
Unsaturated and 13
seawater
monounsaturated
CCMP527 Nannochloropsis
18
salina 16 ACS Paragon Plus Environment
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Page 16 of 38
CCMP537
The results clearly show that the efficiency is strongly influenced by the nature of alga, growth condition and utilization of nutrient. Phosphorus (P) was identified as a key nutrient to determine the biomass productivity when compared to N and C
60
. The difference in total fatty
acid composition was ascribed to the significant difference in the metabolism of lipids within the genus
61
. The changes in fatty acid profile depend on the substrate and culture conditions. Fuel
properties such as oxidative stability, Cetane number, and melting point are directly linked to the length and degree of unsaturation of the fatty acid carbon chain 61. Beevi and Sukumaran 58 successfully utilized glycerol waste as nutrient source, indicating the potential recycling of waste to fuel. It was also found that the biomass productivity was higher in seawater medium when compared to fresh water. Recently, Taleb et al. 62 reported the results of screening reshwater and seawater microalgae strains in a fully controlled photobioreactor. Algal strains were screened based on their culture behavior and bio-mass productivity. The screening process was performed via two steps (Fig. 5): (1) a rapid prescreening step and (2) a final validation step.
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Energy & Fuels
Fig.5. Schematic representation of microalgae screening procedure developed by Taleb et al. 62 Parachlorella kessleri UTEX2229 and Nannochloropsis gaditana CCMP527 were identified as promising freshwater (2.7 x 10-3 kg m-3 d-1 of TAG productivity) and seawater strains (2.3 x 10-3 kg m-3 d-1 of TAG productivity), respectively. The strains of Nannochloropsis genus were mainly composed of nine major fatty acids with varying carbon numbers and unsaturation: myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, eicosanoic acid, arachidonic acid and eicosapentae-noic acid 61. 2.3. Seawater batteries: 18 ACS Paragon Plus Environment
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High cost and limited energy storage of lithium ion batteries are the major reasons for the development of seawater batteries (SB) 63. SB is a kind of power source which employs seawater as an electrolyte
64
. Therefore, SB can be used for undersea vehicles. It has a wide range of
applications in lifebuoys, sonobuoys, torpedoes, life raft, and detection devices. The energy density of SB is higher than the normal batteries. The efficiency of SB highly relies on the corrosion of reactive metal anode in seawater and reduction of oxygen or water in an inert metal cathode (Silver chloride (AgCl) or copper chloride (CuCl)). Magnesium (Mg) based alloys are commonly preferred as anodes due to its high faradic capacity (2.2 Ah.g-1), negative electrode potential (-2.73 V (vs. NHE)) and discharge potential. The electrochemical reactions of Mg alloy can be described as follows: Anode:
Mg
Cathode: 2H2O + 2e-
Mg2+ + 2e-
(5)
2OH- + H2
(6)
The corrosion of Mg anode occurs via H2 evolution and magnesium hydroxide (Mg(OH)2) formation Mg + 2H2O
Mg(OH)2 + H2
(7)
The corrosion characteristic of Mg alloy is greatly influenced by morphology, size and distribution of secondary phases. Besides, the discharge reaction is affected by magnesium hydroxide (Mg(OH)2) formation on the electrode. The corrosion potential, specific energy and discharge performance of Mg alloys have been improved by its doping with other metals (ex. Sn, Pb, Hg, Zn, etc) 65. Table 6 summarizes the H2 production rate of different Mg based alloys. It is observed that most of the research works have been carried out using synthetic seawater.
Table 6. Summary of H2 production efficiency of Mg based alloys using synthetic seawater Alloy
Secondary
Activation Comments
Specific Reference
phase
time (s)
energy (W h/kg)
Mg−9%Al−2.5%Pb α-Mg and β- -
Mg−9%Al−2.5%Pb -
Mg17Al12
anode showed high efficiency
when
compared
to
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66
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Mg−9%Al−5%Pb Mg-6%Al-1%Sn
Mg17(Al,Sn)12 7.7
Mg-6%Al-1%Sn
(for Mg-6%Al-
anode showed high
1%Sn)
and
efficiency
Mg2Sn
(for
compared to Mg-
67
147
68 69
when
Mg-6%Al-
6%Al-5%Sn,
5%Sn)
Mg−6%Al−5%Pb and
94.2
Mg-3%Al-
1%Zn Mg–4%Ga–2%Hg
Mg3Hg
and 5.7
Mg–4%Ga–2%Hg
Mg21Ga5Hg3
showed
high
efficiency
when
compared
to
Mg−6%Al−5%Pb and
Mg-3%Al-
1%Zn
The efficiencies of metal doped Mg alloys are higher than commercial Mg alloys (AP 65, AZ 31). This was attributed to the improved corrosion via the formation of intermetallic phases. The currently available Mg based alloys have low concentration of heavy metals impurities, which is harmful to the environment. Hence, it is important to develop non-toxic Mg alloys with high efficiency. There are no studies have been investigated using natural seawater.
2.2.2. Microbial Cells: (a) Microbial Desalination Cells (MDC): Recently, Saeed et al.
70
and Sophia et al. 71 published comprehensive reviews on MDC.
Microbial desalination cells (MDCs) is an energy efficient and economic technology to achieve desalination, energy production and wastewater treatment in a single reactor. MDC can produce more energy than the energy required for its functioning. It is based on the concept of microbial fuel cell (MFC). It utilizes the microbes present in wastewater to convert bio-chemical energy into electricity
72, 73
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. The schematic diagram of a
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MDC is shown in Fig.6. Wastewater and salt water are fed in the anode and desalination chambers, respectively. A bio-film (accumulation of microbial colonies) is grown on the anode, which acts as an anodic catalyst
74
. At the anode chamber, the bacterium oxidizes the organic
matter and producing protons and electrons. The electrons are captured by the cathode through an external circuit 71. Different types of MDCs such as air cathode, bio-cathode, recirculation, capacitive, upflow, osmotic, bipolar membrane, de-coupled, separator coupled stacked circulation and ionexchange resin coupled have been studied 75-81. Synthetic seawater was used in most of the MDC studies 82-85. Only few researchers used natural seawater and/or actual wastewater
86 87 70, 88
.
Fig.6. The schematic diagram of a MDC 86 Recently, Sevda et al. 86 reported bio-electricity generation using petroleum refinery wastewater effluent and natural seawater (Collected from Doha, Qatar). The power generation and salt removal rate were enhanced in acidic catholyte when compared to neutral catholyte. Zhang and He
87
examined energy production using an up-flow MDC (UMDC) connected to an electro-
dialysis (ED) unit. They suggested that rechargeable batteries are more appropriate to extract energy when compared to external circuit. The required amount of wastewater depends on the initial salinity of water
70, 88
. The electricity generation can be affected by pH, temperature,
volume of water, membrane fouling and electrode stability. The electricity generation was increased by electrolyte recirculation process in MDC 73. 2.2.Electricity generation using seawater: 21 ACS Paragon Plus Environment
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2.2.1. Salinity Gradient Energy (SGE): Salinity gradient energy (SGE) is produced by mixing two solutions of different salinities (e.g., seawater and river water) using pressure-retarded osmosis (PRO), reverse electro-dialysis (RED), capacitive mixing (CAPMIX), and mixing entropy battery (MEB). A comprehensive review on salinity gradient energy published by Jia et al.
89
and Yip et al.
90
. However, a brief
description on the principle and the important results using natural seawater/seawater brine are provided in the following section.
Pressure Retarded Osmosis (PRO): The schematic diagram of a PRO process is shown in Fig. 7
91
. The osmotic pressure
difference between seawater and river water is used to convert SGE to mechanical or electrical energy 92. Water flows from river water side (low concentration (LC) and pressure) to seawater side (high concentration (HC) and pressure) via a semi-permeable membrane in order to make up for the chemical potential equilibrium on both sides. Mechanical energy is generated due to the expansion of volume in the HC compartment and this could be utilized to run a turbine to generate electricity 93, 94. HC and LC solutions are otherwise called as draw and feed solutions, respectively. Table 7 summarizes the results of PRO energy production using natural and synthetic seawater brine as a draw solution.
Fig.7. The schematic diagram of PRO process
91
Table 7. Summary of results for PRO power production using seawater 22 ACS Paragon Plus Environment
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Membrane
HC
LC
Page 22 of 38
Pressure
Power
(bar)
density
Reference
(W m-2) SiO2/poly
Seawater
acrylonitrile
brine
80 mM NaCl
15.2
15.2
95
10 mM NaCl
20
7.0
96
Wastewater
20
4.6
97
20
21.1
97
(1060
mM NaCl) Hollow
fiber Seawater
membrane
brine
(1000
mM NaCl) Thin
film Seawater
composite
– brine*
retentate
polyethersulfone Thin
film Seawater
composite
– brine*
Deionized water
polyethersulfone
*Collected from TuaSpring desalination plant, Singapore.
The results showed that energy production is strongly influenced by the membrane properties and concentration of LC/HC solutions. The performance of membrane is mainly affected by reverse solute permeation, internal concentration polarization and external concentration polarization
95 96
. Using of seawater brine as HC solution has more advantages
such as: retenate is already under high pressure and salinity, energy consumed during RO may be recovered in PRO, and the negative impact of concentrated seawater brine to the environment will be mitigated
97
. Utilizing of treated wastewater as the feed solution is also an attractive
choice for energy production using PRO (Fig. 8). However, pretreatment of wastewater by ultrafiltration and nano-filtration is beneficial attain higher efficiency 97.
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Fig. 8. The schematic representation of PRO process utilizing wastewater as feed solution 97
More research on PRO technology is underway to minimize concentration polarization and membrane fouling and to enhance the mechanical properties and water permeability in order to make the PRO economically viable.
Reverse electro-dialysis (RED): In RED, HC and LC solutions are pumped into an array of alternating anion exchange membrane (AEM) and cation exchange membrane (CEM). Electrochemical potential is generated by the salinity difference and ionic selectivity of the membrane. The schematic representation of a RED system is shown in Fig. 9. A redox couple (Fe2+/Fe3+) or ion adsorption phenomena in the electrode compartment is used to carry out the current to the external circuit.
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Fig. 9. The schematic representation of RED 98
The design of a RED is significantly distinct from that of electro-dialysis. High flow velocities are required in electro-dialysis to reduce salt depletion at the boundary layers adjacent to the membranes. However, the salt depletion is not an issue in RED, because ions move in the direction of the concentration gradient. The efficiency of RED can be improved by tuning the design of membrane stack. Because the efficiency is influenced by the membrane selectivity (coion transport, water osmosis, and electro-osmosis), intermembrane distance, flow direction of HC/LC solutions, and number of electrode segments 99-101. HC and LC solutions are effectively utilized by the stacks with small inter-membrane distance when compared to the stacks with large inter-membrane distance
99
. However, the
disadvantages of using small inter-membrane distance are: large hydraulic friction of HC compartment and extra pretreatment to avoid fouling. These limitations are rectified with the help of profiled membranes (membrane with ridges). The electromotive force (related to electrical potential), ohmic loss (related to current density) and energy utilization are dependent on the flow direction of HC and LC solutions Vermaas et al.
100
100
.
studied the RED efficiency under different flow orientations such as co-flow
(flow of HC and LC in the same direction), cross-flow (flow in the perpendicular direction), and counter-flow (flow in the opposite direction) (Fig. 10). RED efficiency has the following order: counter flow > cross flow > co-flow. The higher efficiency of counter-flow direction is attributed 25 ACS Paragon Plus Environment
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to: the electromotive force is non-zero at all positions, the concentration difference across the membrane is equally distributed. It was also found that the use of multiple electrode segments will further improve the current density.
Fig. 10. The schematic diagram of different flow directions of seawater and river water in RED 100
Selective membranes with ion conductive spacers and innovative channel design are essential to overcome the resistance and hydrodynamic constraints. Capacitive mixing (CAPMIX): CAPMIX is based on the electrochemical double layer (EDL) capacitor technology. Here, HC and LC solutions do not flow simultaneously to anode and cathode compartments, 26 ACS Paragon Plus Environment
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instead these solutions flow to the same compartment at different times
Page 26 of 38
102, 103
. Energy is
extracted by charging and discharging the porous electrodes using HC and LC solutions. The cyclic process involved in a CAPMIX is shown in Fig. 11 90. The process contains four steps: (i) The electrodes are immersed in HC and they are charged using an external electrical current. Cations and anions are accumulated on the oppositely charged electrode. Hence, EDL capacitance is increased at the electrode surface (ii) The circuit is opened and HC is replaced by LC and therefore, EDL capacitance is decreased (iii) The circuit is closed and the ions are discharged from the electrodes via an external load resistor. The energy produced in step (iii) is higher than that was consumed in step (i). (iv) The circuit is opened and LC is replaced by HC to complete the cyclic process.
Fig.11. The schematic diagram of cyclic process involved in a CAPMIX cell 90
To achieve maximum efficiency, the cyclic process is repeated by reusing the HC and LC solutions until the equilibrium concentration is reached. Ion exchange membranes are also used between the porous electrodes to increase the efficiency. This technology is also known as capacitive donnan potential (CDP) approach. This kind of CAPMIX cells does not need an external electric current. Recently, Hatzell et al.
104
reported energy production using a CDP
approach coupled with a bio-electrochemical system (BES) (Fig. 12). The combination of CDP with BES will increase the energy efficiency. Moreover, energy production and wastewater treatment can be attained at the same time. 27 ACS Paragon Plus Environment
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Fig. 12. (a) The schematic representation of CDP-BES (b) theoretical energy extraction using CDP and CDP-BES 104 Here, the capacitive electrodes are immersed into BES. An ionic filed is generated via the microbial oxidation of organic matter by the exo-electrogenic bacteria. This approach can also be applied for thermolytic solutions. The only drawback is the requirement of expensive ionexchange membrane. CAPMIX is more beneficial in terms of using inexpensive electrodes when compared to RED and PRO. However, the charge leakage, low power density, and intermittent power production are the limitations of this method
105
. To address these limitations, Kim et al
105
developed an efficient and cost effective CAPMIX–concentration flow cell (Fig.13). The advantageous of CAPMIX-concentration flow cell are: using of battery electrodes, continuous power density during cyclic use, expensive ion exchange membranes are not required and achieving high efficiency when compared to normal CAPMIX cell.
28 ACS Paragon Plus Environment
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Fig.13. The schematic representation of a CAPMIX –concentration flow cell 105
Mixing Entropy Battery (MEB): MEB is similar to CAPMIX but instead of using inert porous electrodes, it employs faradic electrodes with high specific capacity and low self-discharge. This technology does not need any expensive ion-exchange membranes. Here, charging and discharging are carried out in LC and HC solutions, respectively. The term “mixing” refers the mixing of two solutions with different salinity (LC and HC solution or river water and seawater). The mixing of these two solutions increases the entropy of the system. The entropic energy is extracted and stored in the form of electrochemical energy. Therefore, it is called as mixing entropy battery. The four steps of cyclic process involved in MEB are (Fig. 14 (a)): (i) the electrodes are immersed in LC and the battery is charged by extracting Na+ and Cl- ions from the respective electrodes, (ii) LC is exchanged with HC, which causes an increase in potential difference between the electrodes, (iii) the battery is discharged when the Na+ and Cl- ions are reincorporated into the respective electrodes, and (iv) the HC is then exchanged with LC, which results in a decrease of potential difference 106. The relationship between the battery cell voltage (∆E) and charge (q) is displayed in Fig. 14 (b). There is no consumption or production of energy during step 2 and 4. However, energy is required to drive the ions for step 1 and energy is produced in the battery at step 3 via the incorporation of ions. 29 ACS Paragon Plus Environment
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Fig. 14 (a) The schematic diagram of cyclic process involved in a MEB (b) relationship between battery cell voltage (∆E) and charge (q) during the cyclic process 106
Ye et al.
107
examined the performance of a plate shaped MEB using waste water
effluent (LC; collected from Palo Alto Regional Water Quality Control Plant, USA) and seawater (HC; collected from Half Moon Bay, CA). The schematic representation of the cyclic process involved in a MEB is shown in Fig.15.
Fig.15. The schematic diagram of cyclic process involved in a MEB using waste water effluent and seawater 107
The charging reactions are given as follows: 30 ACS Paragon Plus Environment
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Cathode: 10Na4Mn9O18 Anode:
4AgCl + 4e-
Page 30 of 38
18Na2Mn5O10 + 4Na+ + 4e-
(8)
4Ag + 4Cl-
(9)
The discharging reactions are given as follows: Cathode: 18Na2Mn5O10 + 4Na+ +4eAnode:
4Ag + 4Cl-
10Na4Mn9O18
(10)
4AgCl + 4e-
(11)
It was found that more cells with high specific capacity and stability are required to achieve maximum efficiency.
3. Summary: This review article provides a detailed description on energy production/conversion technologies using seawater. We can generate energy in the form of H2 (photo-catalysis, PEC, bio-chemical, seawater activated battery), natural-gas (CH4), bio-diesel and electricity (PRO, RED, CAPMIX, MEB, MDC,) using seawater as a medium. Microbial process is the easiest methods to achieve high efficiency when compared to other technologies. Natural seawater was mainly collected from China, Korea, Taiwan, Turkey, Arabia and Spain. Pretreatment (such as microfiltration, nano-filtration and ultra-filtration) of natural seawater avoids the negative effect of impurities. Energy production efficiency is strongly influenced by the physico-chemical properties of materials (morphology, size, crystallinity, porosity, stability, durability, water permeability, surface modifiers/additives, surface area, defects, etc.), reaction conditions (volume of water, pH, salinity, temperature, etc.), reactor design and the formation of byproducts. Numerous studies should be carried out in future to validate the economic and environmental feasibility of each technology, reactor design, optimization reaction conditions, usage of natural seawater and the influence of real environmental conditions.
Acknowledgement: The authors are grateful to Texas A&M University at Qatar and Qatar Foundation for the financial support.
References: 31 ACS Paragon Plus Environment
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1. Armaroli, N.; Balzani, V., Towards an electricity-powered world. Energy & Environmental Science 2011, 4, (9), 3193-3222. 2. Höök, M.; Tang, X., Depletion of fossil fuels and anthropogenic climate change—A review. Energy Policy 2013, 52, 797-809. 3. Shafiee, S.; Topal, E., When will fossil fuel reserves be diminished? Energy Policy 2009, 37, (1), 181-189. 4. Maeda, K., Photocatalytic water splitting using semiconductor particles: history and recent developments. Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2011, 12, (4), 237-268. 5. Chen, T.; Quan, W.; Yu, L.; Hong, Y.; Song, C.; Fan, M.; Xiao, L.; Gu, W.; Shi, W., One-step synthesis and visible-light-driven H 2 production from water splitting of Ag quantum dots/gC 3 N 4 photocatalysts. Journal of Alloys and Compounds 2016, 686, 628-634. 6. López, X. A.; Fuentes, A. F.; Zaragoza, M. M.; Guillén, J. A. D.; Gutiérrez, J. S.; Ortiz, A. L.; Collins-Martínez, V., Synthesis, characterization and photocatalytic evaluation of MWO 4 (M= Ni, Co, Cu and Mn) tungstates. International Journal of Hydrogen Energy 2016, 41, (48), 23312-23317. 7. Fan, M.; Song, C.; Chen, T.; Yan, X.; Xu, D.; Gu, W.; Shi, W.; Xiao, L., Visible-lightdrived high photocatalytic activities of Cu/gC 3 N 4 photocatalysts for hydrogen production. RSC Advances 2016, 6, (41), 34633-34640. 8. Fagan, R.; McCormack, D. E.; Dionysiou, D. D.; Pillai, S. C., A review of solar and visible light active TiO 2 photocatalysis for treating bacteria, cyanotoxins and contaminants of emerging concern. Materials Science in Semiconductor Processing 2016, 42, 2-14. 9. Tian, J.; Zhao, Z.; Kumar, A.; Boughton, R. I.; Liu, H., Recent progress in design, synthesis, and applications of one-dimensional TiO 2 nanostructured surface heterostructures: a review. Chemical Society Reviews 2014, 43, (20), 6920-6937. 10. Wang, H.; Zhang, L.; Chen, Z.; Hu, J.; Li, S.; Wang, Z.; Liu, J.; Wang, X., Semiconductor heterojunction photocatalysts: design, construction, and photocatalytic performances. Chemical Society Reviews 2014, 43, (15), 5234-5244. 11. Moniz, S. J.; Shevlin, S. A.; Martin, D. J.; Guo, Z.-X.; Tang, J., Visible-light driven heterojunction photocatalysts for water splitting–a critical review. Energy & Environmental Science 2015, 8, (3), 731-759. 12. Schneider, J.; Matsuoka, M.; Takeuchi, M.; Zhang, J.; Horiuchi, Y.; Anpo, M.; Bahnemann, D. W., Understanding TiO2 photocatalysis: mechanisms and materials. Chemical reviews 2014, 114, (19), 9919-9986. 13. Lee, K. M.; Lai, C. W.; Ngai, K. S.; Juan, J. C., Recent developments of zinc oxide based photocatalyst in water treatment technology: a review. Water research 2016, 88, 428-448. 14. Vignesh, K.; Rajarajan, M.; Suganthi, A., Visible light assisted photocatalytic performance of Ni and Th co-doped ZnO nanoparticles for the degradation of methylene blue dye. Journal of Industrial and Engineering Chemistry 2014, 20, (5), 3826-3833. 15. Boudjemaa, A.; Popescu, I.; Juzsakova, T.; Kebir, M.; Helaili, N.; Bachari, K.; Marcu, I.C., M-substituted (M= Co, Ni and Cu) zinc ferrite photo-catalysts for hydrogen production by water photo-reduction. International Journal of Hydrogen Energy 2016, 41, (26), 11108-11118. 16. Vignesh, K.; Rajarajan, M.; Suganthi, A., Photocatalytic degradation of erythromycin under visible light by zinc phthalocyanine-modified titania nanoparticles. Materials Science in Semiconductor Processing 2014, 23, 98-103.
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Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
17. Zhuang, B.; Xiangqing, L.; Ge, R.; Kang, S.; Qin, L.; Li, G., Assembly and electron transfer mechanisms on visible light responsive 5, 10, 15, 20-meso-tetra (4-carboxyphenyl) porphyrin/cuprous oxide composite for photocatalytic hydrogen production. Applied Catalysis A: General 2017, 533, 81-89. 18. Vignesh, K.; Suganthi, A.; Rajarajan, M.; Sara, S., Photocatalytic activity of AgI sensitized ZnO nanoparticles under visible light irradiation. Powder technology 2012, 224, 331337. 19. Pan, H., Principles on design and fabrication of nanomaterials as photocatalysts for water-splitting. Renewable and Sustainable Energy Reviews 2016, 57, 584-601. 20. Zou, L.; Wang, H.; Wang, X., High Efficient Photodegradation and Photocatalytic Hydrogen Production of CdS/BiVO4 Heterostructure through Z-Scheme Process. ACS sustainable chemistry & engineering 2017, 5, (1), 303-309. 21. Zeng, Y.; Wang, Y.; Chen, J.; Jiang, Y.; Kiani, M.; Li, B.; Wang, R., Fabrication of highactivity hybrid NiTiO 3/gC 3 N 4 heterostructured photocatalysts for water splitting to enhanced hydrogen production. Ceramics International 2016, 42, (10), 12297-12305. 22. Li, Y.; Lin, S.; Peng, S.; Lu, G.; Li, S., Modification of ZnS 1− x− 0.5 y O x (OH) y– ZnO photocatalyst with NiS for enhanced visible-light-driven hydrogen generation from seawater. International Journal of Hydrogen Energy 2013, 38, (36), 15976-15984. 23. Li, Y.; Gao, D.; Peng, S.; Lu, G.; Li, S., Photocatalytic hydrogen evolution over Pt/Cd 0.5 Zn 0.5 S from saltwater using glucose as electron donor: an investigation of the influence of electrolyte NaCl. International Journal of Hydrogen Energy 2011, 36, (7), 4291-4297. 24. Ji, S. M.; Jun, H.; Jang, J. S.; Son, H. C.; Borse, P. H.; Lee, J. S., Photocatalytic hydrogen production from natural seawater. Journal of Photochemistry and Photobiology A: Chemistry 2007, 189, (1), 141-144. 25. Gao, M.; Connor, P. K. N.; Ho, G. W., Plasmonic photothermic directed broadband sunlight harnessing for seawater catalysis and desalination. Energy & Environmental Science 2016, 9, (10), 3151-3160. 26. DeepanPrakash, D.; Premnath, V.; Raghu, C.; Vishnukumar, S.; Jayanthi, S.; Easwaramoorthy, D., Harnessing power from sea water using nano material as photocatalyst and solar energy as light source: the role of hydrocarbon as dual agent. International Journal of Energy Research 2014, 38, (2), 249-253. 27. Harada, H., Isolation of hydrogen from water and/or artificial seawater by sonophotocatalysis using alternating irradiation method. International Journal of Hydrogen Energy 2001, 26, (4), 303-307. 28. Simamora, A.-J.; Hsiung, T.-L.; Chang, F.-C.; Yang, T.-C.; Liao, C.-Y.; Wang, H. P., Photocatalytic splitting of seawater and degradation of methylene blue on CuO/nano TiO 2. International Journal of Hydrogen Energy 2012, 37, (18), 13855-13858. 29. Simamora, A.; Chang, F.; Wang, H., Photocatalytic splitting of seawater for hydrogen energy. WIT Transactions on Ecology and the Environment 2012, 155, 711-718. 30. Simamora, A.-J.; Chang, F.-C.; Wang, H. P.; Yang, T.-C.; Wei, Y.-L.; Lin, W.-K., H2 fuels from photocatalytic splitting of seawater affected by Nano-TiO2 promoted with CuO and NiO. International Journal of Photoenergy 2013, 2013. 31. Cui, G.; Wang, W.; Ma, M.; Xie, J.; Shi, X.; Deng, N.; Xin, J.; Tang, B., IR-Driven Photocatalytic Water Splitting with WO2–Na x WO3 Hybrid Conductor Material. Nano letters 2015, 15, (11), 7199-7203.
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32. Li, Y.; He, F.; Peng, S.; Lu, G.; Li, S., Photocatalytic H 2 evolution from NaCl saltwater over ZnS 1− x− 0.5 y O x (OH) y–ZnO under visible light irradiation. International Journal of Hydrogen Energy 2011, 36, (17), 10565-10573. 33. Yang, T.-C.; Chang, F.-C.; Wang, H. P.; Wei, Y.-L.; Jou, C.-J., Photocatalytic splitting of seawater effected by (Ni–ZnO)@ C nanoreactors. Marine pollution bulletin 2014, 85, (2), 696699. 34. Horiuchi, Y.; Toyao, T.; Takeuchi, M.; Matsuoka, M.; Anpo, M., Recent advances in visible-light-responsive photocatalysts for hydrogen production and solar energy conversion– from semiconducting TiO 2 to MOF/PCP photocatalysts. Physical Chemistry Chemical Physics 2013, 15, (32), 13243-13253. 35. Ichikawa, S., Photoelectrocatalytic production of hydrogen from natural seawater under sunlight. International Journal of Hydrogen Energy 1997, 22, (7), 675-678. 36. Li, Y.; Wei, X.; Yan, X.; Cai, J.; Zhou, A.; Yang, M.; Liu, K., Construction of inorganic– organic 2D/2D WO 3/gC 3 N 4 nanosheet arrays toward efficient photoelectrochemical splitting of natural seawater. Physical Chemistry Chemical Physics 2016, 18, (15), 10255-10261. 37. Li, Y.; Wang, R.; Li, H.; Wei, X.; Feng, J.; Liu, K.; Dang, Y.; Zhou, A., Efficient and stable photoelectrochemical seawater splitting with TiO2@ g-C3N4 nanorod arrays decorated by Co-Pi. The Journal of Physical Chemistry C 2015, 119, (35), 20283-20292. 38. Li, Y.; Feng, J.; Li, H.; Wei, X.; Wang, R.; Zhou, A., Photoelectrochemical splitting of natural seawater with α-Fe 2 O 3/WO 3 nanorod arrays. International Journal of Hydrogen Energy 2016, 41, (7), 4096-4105. 39. Nam, W.; Oh, S.; Joo, H.; Sarp, S.; Cho, J.; Nam, B.-W.; Yoon, J., Preparation of anodized TiO 2 photoanode for photoelectrochemical hydrogen production using natural seawater. Solar Energy Materials and Solar Cells 2010, 94, (10), 1809-1815. 40. Nam, W.; Oh, S.; Joo, H.; Yoon, J., Preparation of Pt deposited nanotubular TiO 2 as cathodes for enhanced photoelectrochemical hydrogen production using seawater electrolytes. Journal of Solid State Chemistry 2011, 184, (11), 2920-2924. 41. Oh, S.; Nam, W.; Joo, H.; Sarp, S.; Cho, J.; Lee, C.-H.; Yoon, J., Photoelectrochemical hydrogen production with concentrated natural seawater produced by membrane process. Solar Energy 2011, 85, (9), 2256-2263. 42. Joo, H.; Bae, S.; Kim, C.; Kim, S.; Yoon, J., Hydrogen evolution in enzymatic photoelectrochemical cell using modified seawater electrolytes produced by membrane desalination process. Solar Energy Materials and Solar Cells 2009, 93, (9), 1555-1561. 43. Prabaharan, D.; Subramanian, G., Oxygen-free hydrogen production by the marine cyanobacterium Phormidium valderianum BDU 20041. Bioresource technology 1996, 57, (2), 111-116. 44. Prabaharan, D.; Kumar, D. A.; Uma, L.; Subramanian, G., Dark hydrogen production in nitrogen atmosphere–An approach for sustainability by marine cyanobacterium Leptolyngbya valderiana BDU 20041. International Journal of Hydrogen Energy 2010, 35, (19), 10725-10730. 45. Lee, J. Z.; Klaus, D. M.; Maness, P.-C.; Spear, J. R., The effect of butyrate concentration on hydrogen production via photofermentation for use in a Martian habitat resource recovery process. International Journal of Hydrogen Energy 2007, 32, (15), 3301-3307. 46. Cai, J.; Wang, G.; Li, Y.; Zhu, D.; Pan, G., Enrichment and hydrogen production by marine anaerobic hydrogen-producing microflora. Chinese Science Bulletin 2009, 54, (15), 26562661.
34 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
47. Cai, J.; Wang, G.; Pan, G., Hydrogen production from butyrate by a marine mixed phototrophic bacterial consort. International Journal of Hydrogen Energy 2012, 37, (5), 40574067. 48. Taikhao, S.; Incharoensakdi, A.; Phunpruch, S., Dark fermentative hydrogen production by the unicellular halotolerant cyanobacterium Aphanothece halophytica grown in seawater. Journal of applied phycology 2015, 27, (1), 187-196. 49. Costa, J. C.; Oliveira, J. V.; Pereira, M. A.; Alves, M. M.; Abreu, A. A., Biohythane production from marine macroalgae Sargassum sp. coupling dark fermentation and anaerobic digestion. Bioresource technology 2015, 190, 251-256. 50. Schramm, W.; Lehnberg, W., Mass culture of brackish-water-adapted seaweeds in sewage-enriched seawater. II: Fermentation for biogas production. Hydrobiologia 1984, 116, (1), 282-287. 51. Miura, T.; Kita, A.; Okamura, Y.; Aki, T.; Matsumura, Y.; Tajima, T.; Kato, J.; Nakashimada, Y., Evaluation of marine sediments as microbial sources for methane production from brown algae under high salinity. Bioresource technology 2014, 169, 362-366. 52. Marquez, G. P. B.; Reichardt, W. T.; Azanza, R. V.; Klocke, M.; Montaño, M. N. E., Thalassic biogas production from sea wrack biomass using different microbial seeds: cow manure, marine sediment and sea wrack-associated microflora. Bioresource technology 2013, 133, 612-617. 53. Fan, X.; Guo, R.; Yuan, X.; Qiu, Y.; Yang, Z.; Wang, F.; Sun, M.; Zhao, X., Biogas production from Macrocystis pyrifera biomass in seawater system. Bioresource technology 2015, 197, 339-347. 54. Elsey, D.; Jameson, D.; Raleigh, B.; Cooney, M. J., Fluorescent measurement of microalgal neutral lipids. Journal of microbiological methods 2007, 68, (3), 639-642. 55. Li, Y.; Horsman, M.; Wu, N.; Lan, C. Q.; Dubois‐Calero, N., Biofuels from microalgae. Biotechnology progress 2008, 24, (4), 815-820. 56. Ozkan, A.; Kinney, K.; Katz, L.; Berberoglu, H., Reduction of water and energy requirement of algae cultivation using an algae biofilm photobioreactor. Bioresource technology 2012, 114, 542-548. 57. Zhao, L.; Qi, Y.; Chen, G., Isolation and characterization of microalgae for biodiesel production from seawater. Bioresource technology 2015, 184, 42-46. 58. Beevi, U. S.; Sukumaran, R. K., Cultivation of the fresh water microalga Chlorococcum sp. RAP13 in sea water for producing oil suitable for biodiesel. Journal of applied phycology 2015, 27, (1), 141-147. 59. Popovich, C. A.; Damiani, C.; Constenla, D.; Martínez, A. M.; Freije, H.; Giovanardi, M.; Pancaldi, S.; Leonardi, P. I., Neochloris oleoabundans grown in enriched natural seawater for biodiesel feedstock: evaluation of its growth and biochemical composition. Bioresource technology 2012, 114, 287-293. 60. Kim, Z.-H.; Park, H.; Ryu, Y.-J.; Shin, D.-W.; Hong, S.-J.; Tran, H.-L.; Lim, S.-M.; Lee, C.-G., Algal biomass and biodiesel production by utilizing the nutrients dissolved in seawater using semi-permeable membrane photobioreactors. Journal of applied phycology 2015, 27, (5), 1763-1773. 61. Taleb, A.; Pruvost, J.; Legrand, J.; Marec, H.; Le-Gouic, B.; Mirabella, B.; Legeret, B.; Bouvet, S.; Peltier, G.; Li-Beisson, Y., Development and validation of a screening procedure of microalgae for biodiesel production: application to the genus of marine microalgae Nannochloropsis. Bioresource technology 2015, 177, 224-232. 35 ACS Paragon Plus Environment
Page 34 of 38
Page 35 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
62. Taleb, A.; Kandilian, R.; Touchard, R.; Montalescot, V.; Rinaldi, T.; Taha, S.; Takache, H.; Marchal, L.; Legrand, J.; Pruvost, J., Screening of freshwater and seawater microalgae strains in fully controlled photobioreactors for biodiesel production. Bioresource technology 2016, 218, 480-490. 63. Kim, J. K.; Lee, E.; Kim, H.; Johnson, C.; Cho, J.; Kim, Y., Rechargeable Seawater Battery and Its Electrochemical Mechanism. ChemElectroChem 2015, 2, (3), 328-332. 64. Wang, N.; Wang, R.; Peng, C.; Peng, B.; Feng, Y.; Hu, C., Discharge and Corrosion Performance of AP65 Magnesium Alloy in Simulated Seawater: Effect of Temperature. Journal of materials engineering and performance 2014, 23, (12), 4374-4384. 65. Wen, L.; Yu, K.; Xiong, H.; Dai, Y.; Yang, S.; Qiao, X.; Teng, F.; Fan, S., Composition optimization and electrochemical properties of Mg-Al-Pb-(Zn) alloys as anodes for seawater activated battery. Electrochimica Acta 2016, 194, 40-51. 66. Min, D.; Wang, R.-c.; Yan, F.; Wang, N.-g.; Wang, L.-q., Corrosion and discharge performance of Mg–9% Al–2.5% Pb alloy as anode for seawater activated battery. Transactions of Nonferrous Metals Society of China 2016, 26, (8), 2144-2151. 67. Kun, Y.; Xiong, H.-q.; Li, W.; Dai, Y.-l.; Yang, S.-h.; Fan, S.-f.; Fei, T.; Qiao, X.-y., Discharge behavior and electrochemical properties of Mg–Al–Sn alloy anode for seawater activated battery. Transactions of Nonferrous Metals Society of China 2015, 25, (4), 1234-1240. 68. Zhao, J.; Yu, K.; Hu, Y.; Li, S.; Tan, X.; Chen, F.; Yu, Z., Discharge behavior of Mg– 4wt% Ga–2wt% Hg alloy as anode for seawater activated battery. Electrochimica Acta 2011, 56, (24), 8224-8231. 69. Yu, K.; Tan, X.; Hu, Y.; Chen, F.; Li, S., Microstructure effects on the electrochemical corrosion properties of Mg–4.1% Ga–2.2% Hg alloy as the anode for seawater-activated batteries. Corrosion Science 2011, 53, (5), 2035-2040. 70. Saeed, H. M.; Husseini, G. A.; Yousef, S.; Saif, J.; Al-Asheh, S.; Fara, A. A.; Azzam, S.; Khawaga, R.; Aidan, A., Microbial desalination cell technology: a review and a case study. Desalination 2015, 359, 1-13. 71. Sophia, A. C.; Bhalambaal, V.; Lima, E. C.; Thirunavoukkarasu, M., Microbial desalination cell technology: Contribution to sustainable waste water treatment process, current status and future applications. Journal of Environmental Chemical Engineering 2016, 4, (3), 3468-3478. 72. Cao, X.; Huang, X.; Liang, P.; Xiao, K.; Zhou, Y.; Zhang, X.; Logan, B. E., A new method for water desalination using microbial desalination cells. Environmental science & technology 2009, 43, (18), 7148-7152. 73. Qu, Y.; Feng, Y.; Wang, X.; Liu, J.; Lv, J.; He, W.; Logan, B. E., Simultaneous water desalination and electricity generation in a microbial desalination cell with electrolyte recirculation for pH control. Bioresource technology 2012, 106, 89-94. 74. Sevda, S.; Yuan, H.; He, Z.; Abu-Reesh, I. M., Microbial desalination cells as a versatile technology: functions, optimization and prospective. Desalination 2015, 371, 9-17. 75. Mehanna, M.; Saito, T.; Yan, J.; Hickner, M.; Cao, X.; Huang, X.; Logan, B. E., Using microbial desalination cells to reduce water salinity prior to reverse osmosis. Energy & Environmental Science 2010, 3, (8), 1114-1120. 76. Wen, Q.; Zhang, H.; Chen, Z.; Li, Y.; Nan, J.; Feng, Y., Using bacterial catalyst in the cathode of microbial desalination cell to improve wastewater treatment and desalination. Bioresource technology 2012, 125, 108-113.
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Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
77. Chen, X.; Liang, P.; Wei, Z.; Zhang, X.; Huang, X., Sustainable water desalination and electricity generation in a separator coupled stacked microbial desalination cell with buffer free electrolyte circulation. Bioresource technology 2012, 119, 88-93. 78. Morel, A.; Zuo, K.; Xia, X.; Wei, J.; Luo, X.; Liang, P.; Huang, X., Microbial desalination cells packed with ion-exchange resin to enhance water desalination rate. Bioresource technology 2012, 118, 43-48. 79. Chen, X.; Xia, X.; Liang, P.; Cao, X.; Sun, H.; Huang, X., Stacked microbial desalination cells to enhance water desalination efficiency. Environmental science & technology 2011, 45, (6), 2465-2470. 80. Zhang, B.; He, Z., Improving water desalination by hydraulically coupling an osmotic microbial fuel cell with a microbial desalination cell. Journal of Membrane Science 2013, 441, 18-24. 81. Zhang, Y.; Angelidaki, I., A new method for in situ nitrate removal from groundwater using submerged microbial desalination–denitrification cell (SMDDC). Water research 2013, 47, (5), 1827-1836. 82. Jacobson, K. S.; Drew, D. M.; He, Z., Use of a liter-scale microbial desalination cell as a platform to study bioelectrochemical desalination with salt solution or artificial seawater. Environmental science & technology 2011, 45, (10), 4652-4657. 83. Luo, H.; Xu, P.; Roane, T. M.; Jenkins, P. E.; Ren, Z., Microbial desalination cells for improved performance in wastewater treatment, electricity production, and desalination. Bioresource technology 2012, 105, 60-66. 84. Ping, Q.; He, Z., Improving the flexibility of microbial desalination cells through spatially decoupling anode and cathode. Bioresource technology 2013, 144, 304-310. 85. Brastad, K. S.; He, Z., Water softening using microbial desalination cell technology. Desalination 2013, 309, 32-37. 86. Sevda, S.; Abu-Reesh, I. M.; Yuan, H.; He, Z., Bioelectricity generation from treatment of petroleum refinery wastewater with simultaneous seawater desalination in microbial desalination cells. Energy Conversion and Management 2017, 141, 101-107. 87. Zhang, B.; He, Z., Energy production, use and saving in a bioelectrochemical desalination system. RSC Advances 2012, 2, (28), 10673-10679. 88. Kim, Y.; Logan, B. E., Microbial desalination cells for energy production and desalination. Desalination 2013, 308, 122-130. 89. Jia, Z.; Wang, B.; Song, S.; Fan, Y., Blue energy: current technologies for sustainable power generation from water salinity gradient. Renewable and Sustainable Energy Reviews 2014, 31, 91-100. 90. Yip, N. Y.; Brogioli, D.; Hamelers, H. V.; Nijmeijer, K., Salinity gradients for sustainable energy: primer, progress, and prospects. Environmental science & technology 2016, 50, (22), 12072-12094. 91. Yip, N. Y.; Elimelech, M., Comparison of energy efficiency and power density in pressure retarded osmosis and reverse electrodialysis. Environmental science & technology 2014, 48, (18), 11002-11012. 92. Logan, B. E.; Elimelech, M., Membrane-based processes for sustainable power generation using water. Nature 2012, 488, (7411), 313-319. 93. Straub, A. P.; Deshmukh, A.; Elimelech, M., Pressure-retarded osmosis for power generation from salinity gradients: is it viable? Energy & Environmental Science 2016, 9, (1), 31-48. 37 ACS Paragon Plus Environment
Page 36 of 38
Page 37 of 38 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
94. Thorsen, T.; Holt, T., The potential for power production from salinity gradients by pressure retarded osmosis. Journal of Membrane Science 2009, 335, (1), 103-110. 95. Song, X.; Liu, Z.; Sun, D. D., Energy recovery from concentrated seawater brine by thinfilm nanofiber composite pressure retarded osmosis membranes with high power density. Energy & Environmental Science 2013, 6, (4), 1199-1210. 96. Zhang, S.; Chung, T. S., Osmotic power production from seawater brine by hollow fiber membrane modules: Net power output and optimum operating conditions. AIChE Journal 2016, 62 (4) 1216-1225. 97. Wan, C. F.; Chung, T.-S., Osmotic power generation by pressure retarded osmosis using seawater brine as the draw solution and wastewater retentate as the feed. Journal of Membrane Science 2015, 479, 148-158. 98. Schaetzle, O.; Buisman, C. J., Salinity gradient energy: current state and new trends. Engineering 2015, 1, (2) 164-166. 99. Vermaas, D. A.; Saakes, M.; Nijmeijer, K., Doubled power density from salinity gradients at reduced intermembrane distance. Environmental science & technology 2011, 45, (16), 7089-7095. 100. Vermaas, D. A.; Veerman, J.; Yip, N. Y.; Elimelech, M.; Saakes, M.; Nijmeijer, K., High efficiency in energy generation from salinity gradients with reverse electrodialysis. ACS sustainable chemistry & engineering 2013, 1, (10), 1295-1302. 101. Yip, N. Y.; Vermaas, D. A.; Nijmeijer, K.; Elimelech, M., Thermodynamic, energy efficiency, and power density analysis of reverse electrodialysis power generation with natural salinity gradients. Environmental science & technology 2014, 48, (9), 4925-4936. 102. Brogioli, D.; Ziano, R.; Rica, R.; Salerno, D.; Kozynchenko, O.; Hamelers, H.; Mantegazza, F., Exploiting the spontaneous potential of the electrodes used in the capacitive mixing technique for the extraction of energy from salinity difference. Energy & Environmental Science 2012, 5, (12), 9870-9880. 103. Brogioli, D., Extracting renewable energy from a salinity difference using a capacitor. Physical review letters 2009, 103, (5), 058501. 104. Hatzell, M. C.; Cusick, R. D.; Logan, B. E., Capacitive mixing power production from salinity gradient energy enhanced through exoelectrogen-generated ionic currents. Energy & Environmental Science 2014, 7, (3), 1159-1165. 105. Kim, T.; Rahimi, M.; Logan, B. E.; Gorski, C. A., Harvesting energy from salinity differences using battery electrodes in a concentration flow cell. Environmental science & technology 2016, 50, (17), 9791-9797. 106. La Mantia, F.; Pasta, M.; Deshazer, H. D.; Logan, B. E.; Cui, Y., Batteries for efficient energy extraction from a water salinity difference. Nano letters 2011, 11, (4), 1810-1813. 107. Ye, M.; Pasta, M.; Xie, X.; Cui, Y.; Criddle, C. S., Performance of a mixing entropy battery alternately flushed with wastewater effluent and seawater for recovery of salinitygradient energy. Energy & Environmental Science 2014, 7, (7), 2295-2300.
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