Promoting Charge Separation and Injection by Optimizing the

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Promoting the Charge Separation and Injection by Optimizing the Interfaces of GaN:ZnO Photoanode for Efficient Solar Water Oxidation Zhiliang Wang, Xu Zong, Yuying Gao, Jingfeng Han, Zhiqiang Xu, Zheng Li, Chunmei Ding, Shengyang Wang, and Can Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b09021 • Publication Date (Web): 23 Aug 2017 Downloaded from http://pubs.acs.org on August 27, 2017

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ACS Applied Materials & Interfaces

Promoting the Charge Separation and Injection by Optimizing the Interfaces of GaN:ZnO Photoanode for Efficient Solar Water Oxidation Zhiliang Wang, a,b ‡ Xu Zong, a,b ‡ Yuying Gao,a,b Jingfeng Han,a Zhiqiang Xu,a,b Zheng Li,a,b Chunmei Ding,a Shengyang Wang a,b and Can Li a* a

State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of

Sciences, Dalian National Laboratory for Clean Energy, The Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Zhongshan Road 457, Dalian, 116023, China. b

University of Chinese Academy of Sciences, Beijing, 100049, China.

KEYWORDS: water oxidation, GaN:ZnO photoanode, charge separation, charge injection, interface, NiCoFeP cocatalyst

ACS Paragon Plus Environment

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ABSTRACT

Photoelectrochemical water splitting provides an attractive way to store solar energy in molecular hydrogen as a kind of sustainable fuels. To achieve high solar conversion efficiency, the most stringent criteria are effective charge separation and injection in electrodes. Herein, efficient photoelectrochemical water oxidation is realized by optimizing charge separation and surface charge transfer of GaN:ZnO photoanode. The charge separation can be greatly improved through modified moisture assisted nitridation and HCl acid treatment, by which the interfaces in GaN:ZnO solid solution particles are optimized and recombination centers existing at the interfaces are depressed in GaN:ZnO photoanode. Moreover, a multimetal phosphide of NiCoFeP was employed as water oxidation cocatalyst to improve the charge injection at the photoanode/electrolyte interface. As a consequence, it significantly decreases the overpotential and brings the photocurrent to a benchmark of 3.9 mA cm-2 at 1.23 V vs RHE and a solar conversion efficiency over 1 % was obtained.


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INTRODUCTION Converting intermittent solar energy into the form of renewable and portable hydrogen fuel via photoelectrochemical (PEC) water splitting describes a prospective future to address serious energy and environmental issues.1 It can realize separated H2 and O2 evolution and high solar conversion efficiency under proper bias.2-4 Semiconductor nanoparticles and nanostructure have been considered as the building blocks of PEC system. And efficient charge generation and transfer in the bulk and charge injection across the electrode/electrolyte interface are at the heart for converting light into fuels.5-7 GaN:ZnO solid solution semiconductor has been regarded as an appropriate candidate for PEC water splitting due to its suitable band gap (2.2-2.6 eV) and band edge position.8-10 But the PEC performance remains quite poor for GaN:ZnO photoanode prepared with traditional methods (e.g., direct nitridation, electrophoretic deposition.11,12) which often result in weak charge transfer in the electrode. Recently, a new synthesis protocol by introducing moisture during nitridation was used to fabricate well connected GaN:ZnO photoelectrodes.13 However, considering the outstanding photocatalytic performance and wide light harvesting ability of GaN:ZnO,8,10,14 the photoelectrode should have endorsed even higher PEC response. The limited charge separation and surface reaction on GaN:ZnO electrode are the obstacles standing in the way toward efficient PEC water splitting. For particulate photoanode, charge transfer across the semiconductor particles is regarded as the key criteria for effective charge separation.15,16 The unregulated interfaces among particles will cause serious charge recombination.17 Furthermore, recombination centers are thought to exist at the interfaces.18 So optimizing the semiconductor interfaces in the particulate electrode is pivotal for achieving high charge separation efficiency.


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Metal phosphide has been reported to be a good oxygen evolution catalyst (OEC).19-22 There has demonstrated an overpotential as low as 248 mV (at 10 mA cm-2) on CoP nanowire.22 Yet, despite the high activity, phosphide based OEC has seldom been applied in PEC water oxidation because of the harsh preparation condition with the presence of high temperature and strong reductive ability. And more effort is appealed for applying this OEC as potential cocatalyst during PEC reaction. Herein, we demonstrate that charge separation can be enhanced via a modified moisture assisted nitridation and HCl acid treatment to depress the interfacial charge recombination. Furthermore, an earth abundant metal phosphide of NiCoFeP is loaded as an oxygen evolution catalyst (OEC) on GaN:ZnO photoanode. The charge injection efficiency of the as-prepared photoanode is profoundly increased. As a result, we obtained 1.2 % solar conversion efficiency under 0.7 V vs RHE and 3.9 mA cm-2 photocurrent at 1.23 V vs RHE. It is the most efficient GaN:ZnO photoanode reported so far.12,23,24 EXPERIMENTAL GaN:ZnO photoanode preparation The precursor electrode is composed of ZnO and Ga2O3. Typically, a mixture of ZnO and Ga2O3 is dip-coated on Ti foil. Then a modified moisture nitridation at 800 oC is performed in the equipments showed in Scheme 1a. Moisture is added by keeping valves of V1 on and V2, V3 off during the heat up stage and stopped at the set time (x h, x=0～2.0) during retention stage (Scheme 1b) by change the status of the valves. The asprepared electrode is denoted as GZ (x h). For detail: GZ(0h) is the GaN:ZnO electrode which does not add moisture during retention at 800 oC. Once the temperature reaches 800 oC, V1 is turned on and V2, V3 turned off.


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GZ(0.5h) is the GaN:ZnO electrode which has been nitridized with moisture maintained for 0.5 h during retention at 800 oC. Then the moisture is stopped by turning on V1 and turning off V2 and V3. And so are the similar cases for GZ(1h) and GZ(1.5h) samples. GZ(2h) is the GaN:ZnO electrode has been nitridized with moisture maintained for 2 h during retention at 800 oC, then moisture is stopped once it starts to cool down. GZwater is the GaN:ZnO electrode with moisture maintained all over the nitridation progress.

Scheme 1. (a) The schematic illustration of the equipment for modified moisture assisted nitridation. (b) The moisture control process during nitridation. When moisture is stopped at set time, the humidity (blue curves) will decrease gradually. The temperature of the reactor is shown in red curves.


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HCl acid treatment The as-prepared GaN:ZnO electrode is immersed in 0.75 M HCl aqueous solution (36~38 wt%, Kermel) with magnetic stirring for 3 hours. Then it was totally washed with deionized water and dried in air. The electrode is denoted as HCl-GZ(x h) where x presents the moisture exposure time (0~2 h) during retention. NiCoFeP cocatalyst loading An aqueous solution containing 10 mM Ni(NO3)2·6H2O (≥98.0 %, Sinopharm), 10 mM Co(NO3)2·6H2O (≥98.0 %, Sinopharm) and 5 mM Fe(NO3)3·6H2O (≥98.0 %, Sinopharm) is used as precursor. Then the as-prepared HCl acid washed electrode was immersed in the solution for 30 minutes to ensure the absorption of the precursor metal ions. Following by, the electrode was phosphorized with NaH2PO2 placing ahead the electrode in a quartz holder at 300 oC for 0.5 h under 10 mL min-1 Ar flow. At high temperature, NaH2PO2 can decompose as follow: NaH2PO2→Na3PO4+PH3 PH3 is able to transfer the absorbed NiCoFe-precusor into phopide of NiCoFeP. RESULTS AND DISCUSSION The performance of photoelectrodes The GaN:ZnO photoelectrodes prepared by modified moisture-assisted nitridation show strong particle connection and similar crystal phase (Figure S1) despite of different moisture exposure time. The PEC performance is evaluated in different aqueous solution in Figure 1. Figure 1a shows the photocurrent (jNaOH) of the pristine electrodes for PEC water oxidation in NaOH aqueous solution. The jNaOH increase along with the decrease of exposure time. GZ(0h) electrode shows a photocurrent of 2.36 mA cm-2 at 1.23 V vs RHE which is more than 2 times that of GZ(2h) electrode. When there presents 0.5 M Na2SO3 serving as hole scavenger in the solution,


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the photocurrent (jNa2SO3) becomes much stronger (Figure 1b). Based on jNaOH and jNa2SO3, the charge separation (ηsep) and injection efficiency (ηinj) can be calculated according to eq. 1: 25-27 jPEC=jabs*ηsep *ηinj (1) The sulphite oxidation kinetic is fast and ηinj is ~100 % for jNa2SO3.26 Therefore, ηsep is obtained by dividing jNa2SO3 by jabs (Figure S2). Figure 1c shows that ηsep increases with decreasing the moisture exposure time. And GZ(0h) photoelectrode has the best charge separation.

Figure 1. (a) The photocurrent of pristine GaN:ZnO photoanodes with different moisture exposure time in 1 M NaOH and (b) 1 M NaOH and 0.5 M Na2SO3 mixed aqueous solution. (c) The charge separation efficiency and (d) the surface photovoltage spectra of the pristine GaN:ZnO photoelectrodes.


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Surface photovoltage spectrum (SPS) is used for further scrutiny of the charge separation in the electrodes. In SPS, a light induced change of the contact potential (photovoltage) of a sample is recorded as a function of the irradiation wavelength. And higher photovoltage indicates more separated electron-hole pairs upon illumination.28, 29 Figure 1d shows that GZ(0h) photoelectrode has the highest photovoltage, while the GZ(2h) the lowest. It suggests that the GZ(0h) photoelectrode has much more efficient charge separation than GZ(2h), which is consistent with ηsep in Figure 1c. Accordingly, decreasing the moisture exposure time during retention is benefit for charge separation in GaN:ZnO photoanodes. After HCl acid treatment, the particle connection and crystal phase change little (Figure S3). But the photocurrent has noticeable improvement in Figure 2a. And the magnitude of photocurrent increase depends on the moisture exposure time. For GZ(0h) electrode, the photocurrent at 1.23 V vs RHE increases from 2.36 mA cm-2 to 2.5 mA cm-2. While for GZ(2h) electrode, it increases from 1.4 mA cm-2 to 3.1 mA cm-2. To the best of our knowledge, this is the highest photoresponse ever achieved on GaN:ZnO-based photoelectrode without loading cocatalyst.23,24 When using Na2SO3 as electrolyte, the photocurrent of HCl acid treated electrodes approach ca. 3.5 mA cm-2 at 1.4 V vs RHE in Figure 2b. And the jNa2SO3 difference caused by the difference of moisture exposure time becomes less prominent than that of the pristine GaN:ZnO photoanodes. Figure 2c shows that the calculated ηsep varies in only 10 % for different HCl acid treated GaN:ZnO photoanodes. It is implied that the charge separation efficiency increases to a similar proportion for all the photoelectrodes. The SPS tests further ascertain the results (Figure 2d) and the HCl-GZ(2h) exhibits the highest photovoltage, in line with the largest charge separation efficiency in Figure 2c.


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Figure 2. (a) The photocurrent of HCl acid treated GaN:ZnO photoanodes with different moisture exposure time in 1 M NaOH and (b) 1 M NaOH and 0.5 M Na2SO3 mixed aqueous solution. (c) The charge separation efficiency and (d) the surface photovoltage spectra of the HCl acid treated GaN:ZnO photoelectrodes. The comparison of charge separation between the pristine and HCl acid treated GaN:ZnO photoanode is shown in Figure 3a. The ηsep at 1.23 V vs RHE is plotted versus the moisture exposure time. For pristine GaN:ZnO photoelectrode, ηsep decreases from 75 % (GZ(0h)) to 28 % (GZ(2h)) when increasing the moisture exposure time. But after HCl acid treatment, all the electrodes have a ηsep of 62 %~71 %. The impact of moisture exposure time seems diminished with HCl acid treatment.


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Figure 3. (a) The influence of moisture exposure time on the charge separation efficiency and (b) Zn content for pristine and HCl acid treated GaN:ZnO photoelectrodes. (c) The relationship between Zn content and charge separation efficiency. The maximum surface photovoltage (SPV) of pristine GaN:ZnO photoelectrodes is presented for comparison.


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The influence of Zn To gain further insight into the influence of moisture exposure time and HCl acid treatment on charge separation, the Zn content in electrodes is analyzed. In Figure 3b, it shows that for pristine GaN:ZnO photoelectrodes, the Zn molar ratio increase from 0.27 (GZ(0h)) to 0.45 (GZ(2h)) by prolonging moisture exposure time. Upon HCl acid treating, all GaN:ZnO photoelectrodes have approximated Zn content of 0.25-0.27 which is independent of the moisture exposure time. By correlating the Zn content with ηsep of all the GaN:ZnO photoelectrode (Figure 3c), it shows a pseudo-linear relationship with a negative slope which means the lower the Zn content is, the higher the charge separation efficiency is in the GaN:ZnO photoelectrodes. When plotting photovoltage in SPS versus Zn content, they obey the similar relationship. Consequently, Zn content plays a vital role in determining the charge separation in GaN:ZnO photoanode. Further elemental mapping of the particles on GZ(2h) photoelectrode shows that the Zn/Ga is not homogeneously distributed in it (Figure 4 a~c). The region where there are more Zn atoms, the Ga atoms seem to be less (Figure 4 b and c, Figure S5f). The area of Zn and Ga distribution is not overlapped. After treating GaN:ZnO electrode in HCl acid, the solid particles (Figure 4d) turns into hollow (Figure 4e and Figure S5 a) structure with Zn/Ga overlapped distribution (Figure S5 b~e). Since GaN and GaN:ZnO solid solution are well acid proof,8,30 it is suspected that Zn is aggregated as ZnO phase in the solid solution and acid treatment can easily remove the excess ZnO, resulting in a hollow structure particle with prominent Zn loss (Figure 4e). Principally, thermal diffusion is the driving force during the solid solution formation, which is controlled by temperature and diffusion duration.31 For all the electrodes, they were prepared at the same nitridation temperature (800 oC) for the same duration (2 h), so there should be about


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the same amount of dissolved ZnO in solid solution. And this result is confirmed in Figure 3b where all the HCl treated GaN:ZnO electrodes have closed Zn ratio. However, for the raw electrodes, the excess ZnO will coexist with the GaN:ZnO solid solution and it may be buried by GaN:ZnO as shown in Figure 4.

Figure 4. (a) HRTEM image of pristine GZ(2h) photoelectrode. (b) and (c) The Zn and Ga elemental mapping of the particle in (a). (d) The HRSEM images of the pristine GZ(2h) and (e) HCl acid treated GZ(2h) photoelectrodes. In case of mixed ZnO and GaN:ZnO, interfaces will be formed between the two phases. For GZ(2h), Moire patterns resulting from lattice mismatch at the boundary32,33 clearly show the phase interfaces in Figure S6. Defect sites may exist at these interfaces which will cause sub-


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bandgap absorption beyond the band edge.34,35 Indeed, the absorption tail (λ>550 nm) suspected to be defect absorption is found in pristine GaN:ZnO electrode (Figure S2 a). For HCl treated electrodes, these undesired interfaces are eliminated by etching the excess ZnO in the electrode. So the defect absorption is negatively observed (Figure S2 b). The photocatalytic performances of the particles peeled from GZ(2h) and HCl-GZ(2h) show the benefit of eliminating phase interfaces on photo charges generation. Figure 5a shows that the photocatalytic oxygen evolution rate is increased from 98 μmol h-1 (GZ(2h)) to 173 μmol h-1 (HCl-GZ(2h)). Since they have similar surface hole injection efficiencies (Figure S4), the prominent increase of photocatalytic O2 evolution should be due to the improved charge generation in the particles after HCl acid treatment.15

Figure 5. (a) The photocatalytic performance of the particles peeled from GZ(2h) and HClGZ(2h) photoelectrodes. (b) The j-V curves of GZ(2h) and HCl-GZ(2h) photoelectrodes. An inserted scheme shows the device for j-V measurement. LED light (λ=385 nm) is used to excite the GaN:ZnO film and two golden wire (Φ=1 mm) is used as collector.


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Moreover, the unregulated phase interfaces have been reported to be recombination centres (possibly through the defect sites) in photoelectrodes.17,18 And they will seriously retard the charge transfer in electrode and impede the transfer of photogenerated charges. In the case of modified moisture assisted nitridation, the Zn content in the electrodes is determined by Zn loss reaction in high temperature ammonia.13 By shortening the moisture exposure time, the Zn loss reaction is promoted and an increased amount of ZnO will be reduced and escapes from GaN:ZnO photoelectrode. So fewer ZnO/GaN:ZnO interfaces remain with shorter moisture exposure time. As for acid treatment, all phase interfaces are eliminated by etching the ZnO in HCl acid, so that the photogenerated charges can transport facilely in the particles. The enhanced charge transfer is confirmed by the j-V curves of the Ti|GZ(2h)|Au and Ti|HCl-GZ(2h)|Au devices in Figure 5b. When V>0, the voltage is applied to the back Ti foil to collect electrons so as to simulate the case in PEC process. When V2% Efficient Water Splitting. Adv. Energy Mater. 2016, 6, 1501645. (5)

Mayer, M. T.; Lin, Y.; Yuan, G.; Wang, D., Forming Heterojunctions at the Nanoscale

for Improved Photoelectrochemical Water Splitting by Semiconductor Materials: Case Studies on Hematite. Acc.Chem. Res. 2013, 46, 1558-1566.


18

Page 19 of 24

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


(6)

Lin, F.; Boettcher, S. W., Adaptive Semiconductor/Electrocatalyst Junctions in Water-

Splitting Photoanodes. Nat. Mater. 2014, 13, 81-86. (7)

Kamat, P. V., Manipulation of Charge Transfer across Semiconductor Interface. A

Criterion That Cannot Be Ignored in Photocatalyst Design. J. Phys. Chem. Lett. 2012, 3, 663672. (8)

Maeda, K.; Takata, T.; Hara, M.; Saito, N.; Inoue, Y.; Kobayashi, H.; Domen, K., Gan:

ZnO Solid Solution as a Photocatalyst for Visible-Light-Driven Overall Water Splitting. J. Am. Chem. Soc. 2005, 127, 8286-8287. (9)

Maeda, K.; Teramura, K.; Lu, D.; Takata, T.; Saito, N.; Inoue, Y.; Domen, K.,

Photocatalyst Releasing Hydrogen from Water. Nature 2006, 440, 295-295. (10)

Lee, K.; Lu, Y.-G.; Chuang, C.-H.; Ciston, J.; Dukovic, G., Synthesis and

Characterization of (Ga1-xZnx)(N1-xOx) Nanocrystals with a Wide Range of Compositions. J. Mater. Chem. A 2016, 4, 2927-2935. (11)

Yan, S. C.; Zou, Z. G., A Porous Zngano Photoanode for Efficient Water Oxidation

Modified by a Co-Based Electrocatalyst. Dalton Trans. 2015, 44, 3856-3861. (12)

Hashiguchi, H.; Maeda, K.; Abe, R.; Ishikawa, A.; Kubota, J.; Domen, K., Photoresponse

of GaN: ZnO Electrode on FTO under Visible Light Irradiation. Bull. Chem. Soc. Jpn. 2009, 82, 401-407. (13)

Wang, Z.; Han, J.; Li, Z.; Li, M.; Wang, H.; Zong, X.; Li, C., Moisture-Assisted

Preparation of Compact GaN:ZnO Photoanode toward Efficient Photoelectrochemical Water Oxidation. Adv. Energy Mater. 2016, 6, 1600864. (14)

Maeda, K.; Teramura, K.; Takata, T.; Hara, M.; Saito, N.; Toda, K.; Inoue, Y.;

Kobayashi, H.; Domen, K., Overall Water Splitting on (Ga1-xZnx)(N1-xOx) Solid Solution


19


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

Page 20 of 24

Photocatalyst: Relationship between Physical Properties and Photocatalytic Activity. J. Phys. Chem. B 2005, 109, 20504-20510. (15)

Wang, Z.; Qi, Y.; Ding, C.; Fan, D.; Liu, G.; Zhao, Y.; Li, C., Insight into the Charge

Transfer in Particulate Ta3N5 Photoanode with High Photoelectrochemical Performance. Chem. Sci. 2016, 7, 4391-4399. (16)

Ma, G.; Liu, J.; Hisatomi, T.; Minegishi, T.; Moriya, Y.; Iwase, M.; Nishiyama, H.;

Katayama, M.; Yamada, T.; Domen, K., Site-Selective Photodeposition of Pt on a Particulate ScLa5Ti2CuS5O7 Photocathode: Evidence for One-Dimensional Charge Transfer. Chem. Commun. 2015, 51, 4302-4305. (17)

Wang, X.; Jin, S.; An, H.; Wang, X.; Feng, Z.; Li, C., Relation between the

Photocatalytic and Photoelectrocatalytic Performance for the Particulate Semiconductor-Based Photoconversion Systems with Surface Phase Junction Structure. J. Phys. Chem. C 2015, 119, 22460-22464. (18)

Li, A. Wang Z., Yin H., Wang S., Yan P., Huang B., Wang X., Li R., Zong X., Han H.

and Li C., Understanding the Anatase-Rutile Phase Junction in Charge Separation and Transfer in a TiO2 Electrode for Photoelectrochemical Water Splitting. Chem. Sci. 2016, 7, 6076-6082. (19)

Stern, L.-A.; Feng, L.; Song, F.; Hu, X., Ni2P as a Janus Catalyst for Water Splitting: The

Oxygen Evolution Activity of Ni2P Nanoparticles. Energy Environ. Sci. 2015, 8, 2347-2351. (20)

Chang, J.; Xiao, Y.; Xiao, M.; Ge, J.; Liu, C.; Xing, W., Surface Oxidized Cobalt-

Phosphide Nanorods as an Advanced Oxygen Evolution Catalyst in Alkaline Solution. ACS Catal. 2015, 5, 6874-6878.


20

Page 21 of 24

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


(21)

Yu, X.-Y.; Feng, Y.; Guan, B.; Lou, X. W.; Paik, U., Carbon Coated Porous Nickel

Phosphides Nanoplates for Highly Efficient Oxygen Evolution Reaction. Energy Environ. Sci. 2016, 9, 1246-1250. (22)

Li W., Gao X., Xiong D., Xia F., Liu J., Song W., Xu J., S. M. Thalluri, M. F. Cerqueira,

Fu X. and Liu L., Vapor-Solid Synthesis of Monolithic Single-Crystalline CoP Nanowire Electrodes for Efficient and Robust Water Electrolysis. Chem. Sci. 2017, 8, 2952-2958. (23)

Zhong, M.; Ma, Y.; Oleynikov, P.; Domen, K.; Delaunay, J.-J., A Conductive ZnO-

ZnGaON Nanowire-Array-on-a-Film Photoanode for Stable and Efficient Sunlight Water Splitting. Energy Environ. Sci. 2014, 7, 1693-1699. (24)

Imanaka, Y.; Anazawa, T.; Manabe, T.; Amada, H.; Ido, S.; Kumasaka, F.; Awaji, N.;

Sánchez-Santolino, G.; Ishikawa, R.; Ikuhara, Y., An Artificial Photosynthesis Anode Electrode Composed of a Nanoparticulate Photocatalyst Film in a Visible Light Responsive GaN-ZnO Solid Solution System. Sci. Rep. 2016, 6, 35593. (25)

Dotan, H.; Sivula, K.; Grätzel, M.; Rothschild, A.; Warren, S. C., Probing the

Photoelectrochemical Properties of Hematite (α-Fe2O3) Electrodes Using Hydrogen Peroxide as a Hole Scavenger. Energy Environ. Sci. 2011, 4, 958-964. (26)

Kim, T. W.; Choi, K.-S., Nanoporous BiVO4 Photoanodes with Dual-Layer Oxygen

Evolution Catalysts for Solar Water Splitting. Science 2014, 343, 990-994. (27)

Wang, Z.; Liu, G.; Ding, C.; Chen, Z.; Zhang, F.; Shi, J.; Li, C., Synergetic Effect of

Conjugated Ni(OH)2/IrO2 Cocatalyst on Titanium-Doped Hematite Photoanode for Solar Water Splitting. J. Phys. Chem. C 2015, 119, 19607-19612.


21


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

(28)

Page 22 of 24

Ye S., Chen R., Xu Y., Fan F., Du P., Zhang F., Zong X., Chen T., Qi Y., Chen P., Chen

Z. Li C., An Artificial Photosynthetic System Containing an Inorganic Semiconductor and a Molecular Catalyst for Photocatalytic Water Oxidation. J. Catal. 2016, 338, 168-173. (29)

Zhu, J.; Fan, F.; Chen, R.; An, H.; Feng, Z.; Li, C., Direct Imaging of Highly Anisotropic

Photogenerated Charge Separations on Different Facets of a Single BiVO4 Photocatalyst. Angew. Chem., Int. Ed. 2015, 54, 9111-9114. (30)

Zhuang, D.; Edgar, J. H., Wet Etching of GaN, AlN, and SiC: A Review. Mater. Sci. Eng.

R 2005, 48, 1-46. (31)

Kim, D.-J., Lattice Parameters, Ionic Conductivities, and Solubility Limits in Fluorite-

Structure MO2 Oxide [M = Hf4+, Zr4+, Ce4+, Th4+, U4+] Solid Solutions. J. Am. Ceram. Soc. 1989, 72, 1415-1421. (32)

Grzelczak, M.; Rodríguez-González, B.; Pérez-Juste, J.; Liz-Marzán, L. M., Quasi-

Epitaxial Growth of Ni Nanoshells on Au Nanorods. Adv. Mater. (Weinheim, Ger.) 2007, 19, 2262-2266. (33)

Huang, L.; Shan, A.; Li, Z.; Chen, C.; Wang, R., Phase Formation, Magnetic and Optical

Properties of Epitaxially Grown Icosahedral Au@Ni Nanoparticles with Ultrathin Shells. CrystEngComm 2013, 15, 2527-2531. (34)

Jackson, W. B.; Amer, N. M., Direct Measurement of GaP-State Absorption in

Hydrogenated Amorphous Silicon by Photothermal Deflection Spectroscopy. Phys. Rev. B 1982, 25, 5559-5562. (35)

Qiu, C. H.; Hoggatt, C.; Melton, W.; Leksono, M. W.; Pankove, J. I., Study of Defect

States in GaN Films by Photoconductivity Measurement. Appl. Phys. Lett. 1995, 66, 2712-2714.


22

Page 23 of 24

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


(36)

Yang, D.; Zhou, L.; Yu, W.; Zhang, J.; Li, C., Work-Function-Tunable Chlorinated

Graphene Oxide as an Anode Interface Layer in High-Efficiency Polymer Solar Cells. Adv. Energy Mater. 2014, 4, 1400591. (37)

Ryu, J.; Jung, N.; Jang, J. H.; Kim, H.-J.; Yoo, S. J., In Situ Transformation of Hydrogen-

Evolving CoP Nanoparticles: Toward Efficient Oxygen Evolution Catalysts Bearing Dispersed Morphologies with Co-Oxo/Hydroxo Molecular Units. ACS Catal. 2015, 5, 4066-4074.


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Promoting Charge Separation and Injection by Optimizing the

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