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Self-driven photoelectrochemical splitting of H2S for S and H2 recovery and simultaneous electricity generation Tao Luo, Jing Bai, Jinhua Li, qingyi zeng, youzhi ji, li qiao, xiaoyan li, and Baoxue Zhou Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b03116 • Publication Date (Web): 03 Oct 2017 Downloaded from http://pubs.acs.org on October 10, 2017

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Environmental Science & Technology

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Self-driven photoelectrochemical splitting of H2S for S and H2

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recovery and simultaneous electricity generation

3

Tao Luo a, Jing Bai

4

Zhou a,b∗

5

a

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800 Dongchuan Rd, Shanghai 200240, China

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b

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Shanghai 200240, PR China

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Abstract:

a∗

, Jinhua Li a, Qingyi Zeng, Youzhi Ji, Li Qiao, Xiaoyan Li, Baoxue

School of Environmental Science and Engineering, Shanghai Jiao Tong University No.

Key Laboratory of Thin Film and Microfabrication Technology, Ministry of Education,

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A novel, facile self-driven photoelectrocatalytic (PEC) system was established for

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highly selective and efficient recovery of H2S and simultaneous electricity production.

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The key ideas were the self-bias function between a WO3 photoanode and a Si/PVC

13

photocathode due to their mismatched Fermi levels and the special cyclic redox reaction

14

mechanism of I-/I3-. Under solar light, the system facilitated the separation of holes in the

15

photoanode and electrons in the photocathode, which then generated electricity. Cyclic

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redox reactions were produced in the photoanode region as follows: I- was transformed

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into I3- by photoholes or hydroxyl radicals, H2S was oxidized to S by I3-, and I3- was then

∗

Corresponding authors: [email protected] (J. Bai) [email protected] (B. Zhou)

ACS Paragon Plus Environment


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reduced to I-. Meanwhile, H+ was efficiently converted to H2 in the photocathode region.

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In the system, H2S was uniquely oxidized to sulfur but not to polysulfide (Sxn-) because of

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the mild oxidation capacity of I3-. High recovery rates for S and H2 were obtained up to

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~1.04 mg h-1 cm-1 and ~0.75 mL h-1 cm-1, respectively, suggesting that H2S was

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completely converted into H2 and S. In addition, the output power density of the system

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reached ~0.11 mW cm-2. The proposed PEC-H2S system provides a self-sustaining,

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energy-saving method for simultaneous H2S treatment and energy recovery.

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Key words: Self-driven; H2S decomposition; PEC; S recovery; electricity generation

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For Table of Contents Only

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INTRODUCTION

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H2S is an extremely flammable, colorless, toxic, irritating, and corrosive gas with a

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strong odor of rotten eggs produced from the fast progress of industrialization, resulting

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in serious environmental pollution and bodily injury1-5. In fact, H2S is a potentially

32

valuable chemical that is rich with H2 and elemental sulfur (S)4. Hence, there is a


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pressing need to dispose of H2S, while simultaneous recycling its waste. In fact, the best

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way to dispose of H2S is to recover H2 and S since the thermodynamic decomposition of

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H2S is only 33 kJ mol-1 (∆G0)4, and some methods, including the thermal decomposition

36

method5, 6, the electrochemical decomposition method1, the plasma method4, 7, and other

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methods, have been reported. However, the existing methods have several shortcomings.

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For instance, the thermal decomposition method requires a temperature higher than

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1,000 °C for the reaction5, 6, the electrochemical decomposition method requires external

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power1, and the plasma method requires complex equipment7. Therefore, an

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environmentally friendly, sustainable and low consumption method for decomposing H2S

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into S and H2 is highly desirable.

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In recent years, photocatalytic8-10 and photoelectrocatalytic (PEC) techniques for

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dealing with environmental pollution have attracted wide attention because these methods

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provide great insight into the utilization of solar energy for degrading pollutants,

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producing hydrogen, and generating electricity11-17. However, in addition to the organic

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waste, few other inorganic pollutants are as concerning as H2S. Traditional PEC

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techniques require an external bias to carry out the PEC process, which means additional

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cost for the external power18-22. Another problem is that S2- can be easily oxidized to

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polysulfide (Sxn-) by the hydroxyl radical (E0 = ~3.2 V vs. NHE) or photoholes (E0 = 3.0

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V vs. NHE) due to their high oxidation potential, resulting in new secondary

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environmental pollution23. Therefore, a specific PEC system for H2S recovery is required.



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Herein, we propose a self-driven PEC H2S system with a special cyclic redox

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reaction mechanism of I-/I3- for the first time. In this system, a WO3 nanoplate was

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selected as the photoanode due to its good visible light absorption and superior

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photoelectronic performance24. A Pt-decorated Si photovoltaic cell (Pt/SiPVC) was

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chosen as the photocathode due to its suitable valence band edge of the p-type Si

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substrate, which will result in a good visible light response25. Together, the photoanode

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and photocathode created a basic self-driven PEC system due to the mismatched Fermi

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levels between the two photoelectrodes. Under illuminating solar light, the system

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facilitated the separation of electron/hole pairs in the two photoelectrodes, and thus, the

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holes of the WO3 photoanode and the electrons of the Si/PVC photocathode could be

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effectively released and generate electricity26. The cyclic redox reactions were set up in

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the photoanode region where I- can be oxidized into I3- 27, 28 (E0 (I3-/I-) = 0.535 V vs. NHE)

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by photoholes or hydroxyl radicals. H2S can be oxidized into S (E0 S/H2S = 0.142 V vs.

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NHE) by I3-, and I3- can then be reduced into I-. Meanwhile, H+ can be reduced very

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efficiently into H2 in the photocathode region. In the system, H2S is uniquely oxidized

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into elemental sulfur (S) but not polysulfide (Sxn-) because I- is a well-known hole or

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hydroxyl-trapping agent29, 30, and the products of I3- are only gentle oxidizers, not strong

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oxidizers31. We also designed an S collection system that was integrated in the PEC

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system to maintain its continuous operation. Overall, the proposed self-driven PEC-H2S

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system provides a sustainable way to recover H2S into S and H2 and to simultaneous

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generate electricity.


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MATERIALS AND METHODS

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Materials. All chemical reagents used in this work were purchased from Sinopharm

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Group CO. LTD and were analytically pure. All solutions were prepared using

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high-purity DI water.

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Synthesis of the nanostructured WO3 nanoplate photoanode. The purchased

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F-doped tin oxide (FTO) substrate (13 Ω cm-1) was cut into 20 mm × 60 mm slides and

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washed under ultrasonication with acetone and deionized water for 30 min. The WO3

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photoanode was prepared via a modified chemical bath deposition method (CBD) 32. In a

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typical process, 0.4 g of Na2WO4•2H2O and 0.15 g of ammonium oxalate were first

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dissolved in 33 mL of deionized water. Then, HCl (9 mL, 37%), H2O2 (8 mL, 30%) and

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ethanol (30 mL) were each subsequently added with strong agitation to obtain the

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precursor solution. The precipitates were dissolved to form a clear solution, and the

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prepared FTO glass (13 Ω cm-1) was dipped into the precursor solution with the FTO side

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facing down. Then, the mixtures were heated to 85 °C in a constant temperature bath and

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naturally cooled down. Finally, the as-prepared sample was rinsed and dried, followed by

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calcination at 500 °C in air for 2 h.

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Fabrication of the Pt/SiPVC photocathode. The Pt/SiPVC photocathode was

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prepared according to our previous work32-34. The backing Al ohmic metal of the

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crystalline Si photovoltaic cell (Shenzhou New Energy) Development Co., Ltd., Shanghai,

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China) was first soldered with a Cu wire and then sealed using an insulating epoxy resin.



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Then, Pt black was decorated on the Ag grids of the Si/PVC via an electrode position

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process in a solution of 1 mM K2PtCl6 and 0.5 M K2SO4 adjusted to pH 1 with H2SO4 at

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-0.4 V.

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Structural Characterization. A field emission scanning electron microscope

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(FE-SEM; Zeiss, Germany, ULTRA PLUS) was used to characterize the surface

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morphology of the WO3 nanoplate photoanode. The crystal phase of the samples was

100

characterized via X-ray diffractometry (XRD) (Bruker, Germany, AXS-8 Advance).

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Optical absorption measurements were performed in a Lamda 750 UV-Vis-IR

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spectrophotometer using an integrating sphere.

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Photoelectrochemical Measurements. The photo response of the WO3/FTO

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photoanode and Pt/SiPVC photocathode was determined using a three-electrode system

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with an Ag/AgCl electrode as the reference, platinum foil as the auxiliary electrode and

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the samples as the working electrode. The working electrode potential and current were

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controlled by an electrochemical workstation (CHI 660c, CH Instruments Inc. 3700

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Tennison Hill Drive Austin, USA). A 350-W Xe lamp was used as the simulated light

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source, without further modification, and all experiments were performed under visible

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light irradiation (light intensity, 100 mWcm−2). The linear sweep voltammograms (LSV)

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were conducted at a scan rate of 10 mV s-1 under chopped light irradiation.

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Apparatus and methods of hydrogen sulfide splitting. A customized double

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chamber reactor with a proton membrane (Bofeilai Technology Co., Ltd.) and a specific


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accessory for S collection was applied for establishing the self-biasing PFC cell. The

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nanostructured WO3 photoanode and Pt photoanode were placed in the anodic and

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cathodic compartments, respectively. The back of WO3/FTO was pressed to the outer

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wall of the anodic compartment to ensure stable light absorption during the entire process.

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Then, 100 mL of 0.5 M H2SO4 containing 0.05-0.3 M KI was used as the electrolyte in

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the anodic compartment and 100 mL of 0.5 M H2SO4 was used as the electrolyte in the

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cathodic compartment. Before operation, nitrogen was piped into the PEC cell for 10 min

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to eliminate air. Under illumination, H2S gas was intermittently pumped into the anodic

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cell, followed by filtration via an S collection accessory, and the filtered solution was

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reinjected into the anodic cell. H2 was gathered and tested using an online gas system

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(Bofeilai Technology Co., Ltd.) connected to a gas chromatograph (GC2010 plus,

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SHIMADZU, Japan).

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RESULTS AND DISCUSSION

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Characterization of the WO3 photoanode and Si The electrodes (photoanode and

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photocathode) used to construct the self-driven PEC system were characterized (Figure 1).

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In terms of the photoanode, Figure 1a shows top-view and cross-section SEM images of

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the WO3 nanoplates. As shown, the WO3 film has a very homogeneous plate-like

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morphology that is perpendicular to the substrate with a thickness of ~850 nm. The

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nanoplate films tightly adhered to the FTO substrate, and the film was directly grown on

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the substrate. As previously reported32, the WO3 nanoplate has an orthorhombic



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crystalline phase and an absorption wavelength of ~450 nm (Figure S1 and Figure S2).

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The IPCE behavior of the WO3 NPA film exhibited in the range of 350 to 470 nm in 0.5

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M H2SO4 solution with 0.2 M KI, which is roughly consistent with the light absorption of

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the WO3 NPA film. This means that the conversion of the incident photons into

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photocurrent occurred successfully in the photoanodes. An IPCE value of ~49% was

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obtained for WO3 at 400 nm (Figure S3). Figure 1c shows the schematic illustration and

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digital photo of the commercial Pt/SiPVC that was used as the photocathode. As shown,

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the backing Al ohmic metal of the PVC was first connected to Cu wires and then

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protected by an epoxy resin. It was subsequently modified using the Pt catalyst via a

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photoassisted electrodeposition method. The Pt catalyst was only deposited on the Ag

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grids, and no Pt catalyst was found on the residual SiNx coating.

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Figures 1b and 1d show the typical LSV curves of the WO3 photoanode and

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Pt/SiPVC photocathode, respectively, in the dark and under AM 1.5 solar light

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illumination (light intensity, 100 mW cm-2) with a 0.5 M H2SO4 electrolyte. Figure 1b

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shows that the WO3 nanoplate has a good photocatalytic capacity under solar light

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irradiation, and the JSC-potential curve of ~0.70 mA cm−2 at a bias of 0.6 V vs. the

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Ag/AgCl reference electrode was observed. The plot in Figure 1d also reveals that

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Pt/SiPVC has an excellent solar light response due to its very short band gap (~2.2 V) due

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to the Si substrate. The ideal onsets of WO3 and Si for photooxidation and photoreduction

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reactions are ~0.65 V and ~-0.4 V, respectively. In view of the JSC-Potential (Figure 1b


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and Figure 1d) and I-T plots (Figure S4), both the photoanode and photocathode show

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favorable photoresponses and good stability for the construction of the H2S-PFC system.

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The self-driven PEC was performed due to matched Fermi levels between the

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photoanode and photocathode, which accounts for the generation of photovoltage in the

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PEC34, 35. Unlike metal electrodes, the Fermi level is located at different positions for

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different types of semiconductors: it is near the conduction band (CB) edge for an n-type

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semiconductor and near the valence band (VB) edge for a p-type semiconductor.

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Therefore, the VOC values could have a difference of Fermi levels between the two

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electrodes. As reported elsewhere36-39, the conduction band and valence band edge of

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WO3 are located at approximately -0.5 V to 0 V and 2.5 V to 3.0 V, respectively, vs.

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NHE. The band gap of WO3 is approximately 3 V. The n-type semiconductor photoanode

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should have a positively located VB edge with an energy level that is sufficient for water

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oxidation. In contrast, a p-type semiconductor photocathode should have a negatively

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located CB edge with an energy level that is sufficient for water reduction. The

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band-edge positions of the WO3 and Si photoelectrodes can be matched to allow

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electrons to migrate from the photoanode to the photocathode. According to the optical

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absorption spectra and the reported energy band level of the semiconductors, the energy

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band positions of the photoanode and photocathode are illustrated in Figure 2a. As shown,

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the Fermi level of WO3 is more negative than that of Si/PVC (0.3 V vs. NHE vs 0.6 V vs.

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NHE) so the electrons generated from WO3 and the holes generated from Si/PVC can be



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driven to be combined with each other by an interior bias through the external circuit.

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Meanwhile, the holes of the photoanode and the electrons of the photocathode can be

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released to produce redox reactions in the solution. This process could be very efficient

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considering the high self-bias, consequently reducing the combination of photogenerated

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electron-hole pairs in both the photoanode and photocathode.

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Figure 2b shows the configuration and operating mechanism of the PEC-H2S system.

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The photoanode and photocathode were placed in the anodic cell and cathodic cell,

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respectively and were separated by a proton exchange membrane. During the operation,

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both photoelectrodes were simultaneous illuminated, and H2S gas was injected into the

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anodic cell while elemental S was collected via an external portion. Special I-/I3- cyclic

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redox reactions40, 41, 21 were set up in the photoanode region, in which I- can be oxidized

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into I3- by photoholes or hydroxyl radicals, H2S can be oxidized into S by I3-, and I3- can

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then be reduced into I-. Meanwhile, H+ was reduced to H2 in the photocathode region.

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The mechanisms of the reactions in the PEC-H2S system can be summarized as equations

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(1)-(9), which were conducted in the two cells. In the anodic cell, the redox couple of

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I-/I3- plays a key role that links the photoelectrochemical reaction and chemical reaction.

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Under illumination, the photogenerated holes (h+) and hydroxyl radical from WO3 first

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oxidize I- to I3- (Eq.1-4); then, I3- efficiently traps and selectively converts H2S to S and

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protons and finally converts into I- (Eq.5). In the cathodic cell, the photogenerated

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electrons (e-) from Pt/SiPVC can reduce protons to generate H2 (Eq.7-8). Overall, with


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the connected redox couples (I-/I3-), the released holes of the WO3 photoanode and the

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released electrons of the Si PVC photocathode can make H2S splitting and energy

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recovery possible using solar energy. WO3 + hv → e- + h+

(1)

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H2O + h+ → HO⋅ + H+

(2)

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3I- + 2 h+ → I3-

(3)

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3I- + 2⋅OH → I3- + 2OH-

(4)

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I3- + H2S → 3I- + 2H+ + S↓

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OH- + H+ → H2O

(6)

SiPVC + hv → e- + h+

(7)

2H+ + 2e- →H2↑

(8)

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Anodic cell:

Cathodic cell:

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H2S → H2↑+ S↓

(5)

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Overall:

(9)

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Figure 3a shows the ion percentages of I- and I3- during the operation of the system

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in 100 mL of 0.5 M H2SO4 solution with 0.2 M KI, and Figure 3b shows the contrasting

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experiment conducted in 100 mL of 0.5 M H2SO4 solution containing 0.2 M KI with 0.1

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mM methyl alcohol as the scavenger. According to the equations above (Eq.1-Eq.9), I3-

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was accumulated, and I- was simultaneous consumed during the initial operation over



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6000 seconds. When H2S was introduced into the anodic cell, I3- reacted with H2S and

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turned back into I-; meanwhile, S was produced. Afterwards, the system ran into the

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second cycle (Figure 3a), and the concentration ratio between I- and I3- presented a

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dynamic equilibrium. In contrast, a scavenger, which can capture photogenerated holes

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(h+) as well as hydroxyl radicals (OH⋅), was added into the anodic cell to investigate the

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effect of the photogenerated holes (h+) and the hydroxyl radicals (OH⋅) on the oxidation

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of I-. As indicated in Figure 3b, the I3- formation rate was far smaller with the existence of

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methyl alcohol, which means that I- can easily oxidize into I3- via photogenerated holes

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(h+) and hydroxyl radicals (OH⋅).

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Based on the proposed principle, H2SO4 was chosen as the basic electrolyte in both

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cells, and KI was added into the anodic cell for H2S oxidation. Thus, we first investigated

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the photoelectric properties of the PEC system under different concentrations of H2SO4

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and KI. The change of the photocurrent density in the system depends on the

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concentration of I- and H2SO4, higher concentration of H2SO4 and I- would both lead to

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higher photocurrent density. In order to show the influence of those two factors on the

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photocurrent density intuitively, we draw a three-dimensional stereogram (Figure 4a). As

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shown in Figure 4a, with the same concentration of sulfuric acid, the photocurrent tended

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to increase as the concentration of KI gradually increased and reached the highest value

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of 0.95 mA cm-2 at 0.25 M KI. Although the current density under 0.25 M KI is slightly

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higher than that under 0.2 M KI, the increment is not considerable. However, KI is


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expensive. We used 0.2 M KI, taking economic factors into account. Since I- can be

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easily oxidized by H+, more electrons could be generated and transferred to the electrode,

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leading to an increase in the photocurrent. However, the nature of the photoanode limited

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the amount of H+, thus further increasing the concentration of I- could not increase the

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photocurrent. Similarly, a higher concentration of H+ led to a higher photocurrent. The

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stability of the electrode was tested, and the results show that the current density reduced

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from 0.95 mA cm-2 to 0.70 mA cm-2 during the initial progress, and the current density

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tended to be stable (Figure S5).

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Accordingly, the concentration of electrolyte also determines the bias potential

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between the photoanode and photocathode. As a key index, the open-circuit voltage (VOC)

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was therefore investigated, and the results are shown in Figure 4b. The VOC values were

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-0.1 V under dark and increased to 0.2 V under illumination without KI. Then, the VOC

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gradually increased with the addition of KI. As shown, the VOC values were 0.27 V, 0.3 V,

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0.33 V and 0.45 V at 0.05 M KI, 0.1 M KI, 0.15 M KI and 0.2 M KI, respectively. In

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particular, the instantaneous open-circuit voltage at 0.2 M KI is ~0.45 V, which is close to

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the theoretical VOC (0.53 V) of the WO3-Si/PVC system. This result indicates that the

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WO3/FTO-Si/PVC system can be driven by the interior bias between the two

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photoelectrodes.

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Figure 5 shows the variation in the photocurrent and the corresponding color change

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of the solution during the entire process under visible light illumination. In the initial



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stage, the photocurrent was approximately 0.7 mA cm-2, and H2 bubbles were observed in

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the cathode cell as the color of solution in the anodic cell gradually turned from

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transparent to light yellow and to bright red, indicating the generation of I3-. After a

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quantity of H2S was injected into the anodic cell, the photocurrent sharply dropped to 0.1

255

mA cm-2 as the bright red solution rapidly turned to a turbid solution that was milky white

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(Figure 5, Figure S6). This finding is attributed to the formation of elemental S, which is

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known to be insoluble in water, and its density is bigger than that of water. This result

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also explained that the oxidation of H2S by I3- is much faster than the oxidation of I-. The

259

solution was then rapidly filtered out, and a colorless and transparent solution was

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obtained again. simultaneous, the photocurrent returned to 0.7 mA cm-2. As shown in

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Figure 5, this phenomenon may be constantly proceeded by a long-term and more

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substantial elemental collection of S (Figure 5b). During the entire process, the

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photocurrent was maintained at 0.7 mA cm-2, except when H2S was injected into the

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solution, leading to a sharp drop. Thus, the I3- could react with H2S to rapidly recover S,

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which, meanwhile, was restored to the reduced state of I- at the end of the cycle. A control

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trial was conducted without the I-/I3- cycle in the anodic cell to determine the formation

267

of polysulfide (Sxn-). A yellow-clear but turbid solution was only obtained during the

268

operation, which is the typical feature of polysulfide solutions (Figure S7). The

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polysulfide could be further confirmed via qualitative analysis of hydrochloric acid in

270

which milky-white turbidity was produced when the yellow-clear solution reacted with

271

the dilute solution of hydrochloric acid. The result illustrated that H2S was easily


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converted into polysulfide (Sxn-) without the existence of I-/I3-.

273

To evaluate the performance of the PEC-H2S system, hydrogen and sulfur were

274

continuously collected during long-term operation. Figure 6a shows the production rate

275

of H2 and S by the PEC-H2S system. The production rates of H2 and S were maintained at

276

~0.0131 mmol h-1 cm-2 and ~0.0135 mmol h-1 cm-2, respectively, suggesting that H2S was

277

completely converted into H2 and S (Table S1). Moreover, the Faradaic efficiency for H2

278

was calculated to be ~99% through the formula below.

279

Faraday Efficiency =

m ( H 2 ) ⋅ n (e) ⋅ F ( F , Faradaycon s tan t ) I ⋅T

280

The m(H2) represent the molar number of hydrogen, n(e) represent the reaction 281

electron number. I and T represent the photocurrent of the system and operation time of 282

the system, respectively.

283

In contrast, the production of sulfur was examined with 0.1 M H2S pumping into the

284

I3- solution. We found that the productivity of S was ~0.09 M, which means S was

285

absolutely generated by I3-. The effect of the photoanode on the elemental S before S was

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filtered from the solution was also investigated. Similarly, SO42- can react with Ba2+ and

287

generate BaSO4 precipitate. The amount of SO42- was calculated by weighing the weight

288

of BaSO4. When S was filtered from the solution, ~11.5 g of BaSO4 was obtained after

289

ample BaCl2 was added. However, it yielded ~60 g of BaSO4 when S remained in the

290

system, which means that S was transformed into SO42- if it remained in the solution.



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In addition, the test also demonstrates that the system possesses good stability and

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reusability. The electricity generation was investigated by evaluating the output power

293

density (Pmax) of the PEC-H2S system as shown in Figure 6b. Pmax can be calculated using

294

the following formula:

Pmax=FF×JSCVOC

295

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Pmax and JSC represent the real maximum power density and theoretical maximum

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power density yielded from the PEC-H2S system, respectively. JSC, VOC and FF are the

298

short-circuit current density, the open-circuit voltage and fill factor of the PEC-H2S

299

system. As shown, the maximum output power density of the PEC-H2S system was ~0.11

300

mW cm-2. The illuminated area of anode and cathode are both 2 cm2. The light energy

301

conversion efficiency was 0.56%.

302

Overall, we described a novel self-driven PEC-H2S system using a WO3 nanoplate

303

as the photoanode and a Pt-decorated Si photovoltaic cell (Pt/SiPVC) as the photocathode

304

for decomposing H2S and obtaining H2 and S with simultaneous electricity production.

305

The performance of the self-driven PEC-H2S system was studied by measuring the

306

photoelectric effect and the production of S and H2. The results demonstrated that the

307

photocurrent and the open-circuit potential could reach 0.7 mA cm-2 and 0.36 V,

308

respectively. Meanwhile, H2 bubbles were observed in the cathode cell, and the unique

309

solid S product was recovered via an external centrifugal circulation system. The novel

310

self-driven PEC-H2S system is promising for sustainable waste recovery and green


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energy generation.

312

ASSOCIATED CONTENT

313

Supporting Information is available free of charge on the ACS Publications website.

314

Figures S1−S6 and Table S1 (PDF)

315

AUTHOR INFORMATION

316

Corresponding Author

317

E-mail: [email protected]; [email protected];

318

phone: 021-54747351; 021-54747364

319

Notes

320

The authors declare no competing financial interests.

321

ACKNOWLEDGEMENTS

322

The authors would like to acknowledge the National Natural Science Foundation of

323

China (No. 21507085), the Shanghai Yangfan Program (14YF1401500) and the

324

SJTU-AEMD for support.

325

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Aid

of

to

Homoallylic Dinuclear

Environmental

and

Allylic

Alcohols

Peroxotungstate.

Preservation.

with

Hydrogen

Cheminform

Cheminform

2009,

2009,

441


64,

Peroxide 131,

(9),

(20),

Catalyzed 6997,

1285-1290,

by

DOI:

DOI:


442 443 444 445

Figure 1. (a) SEM image of WO3/FTO; (b)chopped JSC -Potential curves of WO3 under visible light illumination; (c) schematic diagram of the Si/PVC cathode; (d) chopped JSC-Potential curves of the Si/PVC photoanode photocathode system.

446 447 448

Figure 2. (a) Band-Energy diagram of the PEC system comprising the WO3/FTO photoanode and Pt/SiPVC photocathode; (b) schematic diagram of the PEC-H2S system.


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449

450

Figure 3. (a) Ion percentage of I- and I3- during the operation of the system; (b) ion

451

percentage of I- and I3- during the operation of the system with a scavenger in the anodic

452

cell.

453

454

Figure 4. Current and open-circuit potential under different concentrations of

455

sulfuric acid and potassium I-; (a) current histogram; (b) VOC of the PEC under different

456

conditions.



457 458 459

Figure 5. (a) Change in current during the system operation; (b) color change of the electrolyte in the anode chamber and sulfur compounds separated via centrifugation.

460 461 462

Figure 6. (a) Production of hydrogen and sulfur during long-term operation; (b) I–V characteristic curve and power density curve of the PEC-H2S system.


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Self-Driven Photoelectrochemical Splitting of H - ACS Publications

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