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DOI: 10.1002/cssc.201701663

Solar Water Splitting Utilizing a SiC Photocathode, a BiVO4Photoanode, and a Perovskite Solar Cell
Akihide Iwase,[a, b] Akihiko Kudo,*[a, b] Youhei Numata,[c] Masashi Ikegami,[c]Tsutomu Miyasaka,*[c] Naoto Ichikawa,[d] Masashi Kato,*[d] Hideki Hashimoto,[e] Haruo Inoue,[f]Osamu Ishitani,[g] and Hitoshi Tamiaki[h]We have successfully demonstrated solar water splitting using
a newly fabricated photoelectrochemical system with a Ptloaded SiC photocathode, a CoOx-loaded BiVO4 photoanode,
and a perovskite solar cell. Detection of the evolved H2 and O2
with a 100 % Faradaic efficiency indicates that the observed
photocurrent was used for water splitting. The solar-to-hydrogen (STH) efficiency was 0.55 % under no additional bias conditions.

Photoelectrochemical water splitting is an attractive reaction
to convert solar energy to chemical energy, the so-called artificial photosynthesis. In a photoelectrode system, electric bias
can be applied between a photoanode and a photocathode.
Moreover, H2 is obtained separately from O2 in the photoelectrode system. There are many visible-light-driven photocathodes such as CuI-containing metal sulfides[1–6] and selenides,[7, 8]
Rh-doped SrTiO3,[9] CaFe2O4,[10] and SiC;[11–13] and photoanodes
such as WO3,[14–16] BiVO4,[17–24] Fe2O3,[25–27] SnNb2O6,[28] TaON,[29]Ta3N5,[30–33] LaTiO2N,[34, 35] BaTaO2N,[36, 37] and SrNbO2N.[38, 39]
Herein, we focused on SiC as a photocathode and BiVO4 as aphotoanode. To construct a photoelectrode system; the photocurrent density, onset potential of the photocurrent, and stability are important factors. CuI-containing metal sulfides and selenides give excellent cathodic photocurrents, although their[a] Prof. A. Iwase, Prof. A. Kudo
Department of Applied Chemistry, Faculty of Science
Tokyo University of Science
1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601 (Japan)
E-mail: a-kudo@rs.kagu.tus.ac.jp

onset potentials are not very positive.[1–8] Moreover, the chemical instability in water of metal sulfides and selenides still remains an issue.[2, 6, 7] Chemically stable metal oxides of Rhdoped SrTiO3 and CaFe2O4 possess largely positive onset potentials, whereas the photocurrents are low.[9, 10] From thispoint of view, the SiC with relatively positive onset potential(1.15 V vs. RHE), high photocurrent, and high stability is a suitable candidate as a photocathode in the photoelectrochemical
water splitting system.[13] Regarding the photoanode candidate, BiVO4 shows the most negative onset potential and highphotocurrent under simulated sunlight irradiation.
To achieve high solar energy conversion efficiency, the useof a wide range of sunlight, especially visible light, is important. A weak point of the SiC and BiVO4 is the relatively wideband gap of 2.4–2.5 eV (about 500 nm) as visible-light-responsive materials. Because transparent SiC and BiVO4 photoelectrodes can be prepared,[12, 20] we focus on their combination witha perovskite solar cell to overcome this issue.[40, 41] In moredetail, the perovskite solar cell can absorb transmitted lightthrough the transparent SiC and/or BiVO4 photoelectrodes, because it can utilize visible light up to about 800 nm. Moreover,the photovoltage of about 1.1 V can be used for the photoelectrochemical system to assist water splitting. Actually, there
are some reports about the combined system of a perovskite
solar cell with a BiVO4 photoelectrode for water oxidation to

Tokyo Metropolitan University
2-1 Gakuen, Sanada, Hyogo 669-1337 (Japan)[f] Prof. H. Inoue
Graduate School of Engineering
Toin University of Yokohama
1-1 Minami-ohsawa, Hachioji, Tokyo 192-0397 (Japan)[b] Prof. A. Iwase, Prof. A. Kudo
Photocatalysis international Research Center
Research Institute for Science and Technology
Tokyo University of Science
2641 Yamazaki, Noda-shi, Chiba 278-8510 (Japan)[g] Prof. O. Ishitani
Department of Chemistry, School of Science
Tokyo Institute of Technology
O-okayama 2-12-1-NE-1, Meguro-ku, Tokyo 152-8550 (Japan)[c] Prof. Y. Numata, Prof. M. Ikegami, Prof. T. Miyasaka
Graduate School of Engineering
Toin University of Yokohama
1614 Kurogane-cho, Aoba, Yokohama, Kanagawa 225-8503 (Japan)
E-mail: miyasaka@toin.ac.jp[h] Prof. H. Tamiaki
Graduate School of Life Sciences
Ritsumeikan University
Kusatsu, Shiga 525-8577 (Japan)
Supporting Information and the ORCID identification number(s) for theauthor(s) of this article can be found under https://doi.org/10.1002/
cssc.201701663.

[d] N. Ichikawa, Prof. M. Kato
Department of Engineering Physics, Electronics and Mechanics
Nagoya Institute of Technology
Nagoya 466-8555 (Japan)
E-mail: kato.masashi@nitech.ac.jp[e] Prof. H. Hashimoto
Department of Applied Chemistry, Graduate School of Urban Environmental
Science, Center for Artificial Photosynthesis

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This publication is part of a Special Issue on the topic of Artificial Photosynthesis for Sustainable Fuels. To view the complete issue, visit:
http://dx.doi.org/10.1002/cssc.v10.22.

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Communications
O2.[42–45] In all reports, Pt was used as a cathode for water reduction to H2. Ideally, a photoelectrode should also be used
for the cathode in the photoelectrochemical system. Here, we
demonstrated photoelectrochemical solar water splitting using
a SiC electrode as a photocathode. The SiC photocathode wascombined with a BiVO4 photoanode to split water without any
external bias. A perovskite solar cell was also employed to utilize transmitted light through SiC and/or BiVO4 photoelectrodes and to supply electric assistance for boosting water splitting.
A Pt-loaded SiC (Pt/SiC) photoelectrode gave excellent
cathodic photocurrents in both aqueous phosphate (pH 6.8)
and borate (pH 9.1) buffer solutions under simulated sunlightirradiation, as shown in Figure 1 a. The onset potential versus
reversible hydrogen electrode (RHE) and photocurrent density
in the phosphate solution (pH 6.8) were almost the same as
those in the borate buffer solution (pH 9.1). Thus, we haveconfirmed that the relative position between the band levelsof SiC and the water redox potentials does not change depending on the pH, as previously reported.[11] The onset potential for the cathodic photocurrent was 1.2 V versus RHE, whichis in agreement with the reported value of 1.15 V versus
RHE.[13] This quite positive onset potential is favorable for fabricating a two-electrode photoelectrochemical cell for water
splitting. An onset potential greater than 1.23 V versus RHE is

the thermodynamic requirement to reduce water to H2 without assistance of external bias for a photocathode material.
In other words, only a small assistance is necessary forwater splitting using the Pt/SiC photoelectrode. From thispoint of view, the photovoltage of about 1.1 V of a
(FAPbI3)0.85(MAPbBr3)0.15 perovskite solar cell is large enough.[46]Moreover, the absorption edges of SiC and the (FAPbI3)0.85(MAPbBr3)0.15 perovskite solar cell were 500 and 800 nm,
respectively (Figure S1 in the Supporting Information). Thus, it
is expected that the solar cell can efficiently utilize the transmitted light in the range of 500–800 nm through the Pt/SiC
photoelectrode. Actually, the perovskite solar cell showed aphotovoltage of about 1.1 V, as shown in Figure 1 b, evenunder irradiation of simulated sunlight through the Pt/SiC photoelectrode.
A two-electrode photoelectrochemical cell was constructedusing the Pt/SiC photocathode and a counter electrode.
Figure 2 shows the observed photocurrents under applied bias

Figure 2. Measured current using a two-electrode system with a Pt/SiC photocathode and an oxygen-evolving anode in the presence and absence of a
(FAPbI3)0.85(MAPbBr3)0.15 perovskite solar cell. The solar cell was irradiatedwith transmitted light through the Pt/SiC photoelectrode. Solid and dashedlines represent the current under illumination and in the dark, respectively.
The triangles indicate onset bias of photocurrents. Light source: solar simulator (AM 1.5G); electrolyte: aqueous borate buffer solution (pH 9.1).

Figure 1. a) Current–potential curves of a Pt-loaded SiC photoelectrodein phosphate (pH 6.8) or borate (pH 9.1) buffer aqueous solutions undersimulated sunlight irradiation. b) Current–voltage curves of a
(FAPbI3)0.85(MAPbBr3)0.15 perovskite solar cell under simulated sunlightirradiation with and without Pt/SiC or CoOx/BiVO4 filters. Light source:
solar simulator (AM 1.5G).

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in the presence and absence of a (FAPbI3)0.85(MAPbBr3)0.15 perovskite solar cell. In the absence of the solar cell, a photocurrent was not observed under no-bias conditions, as expectedfrom Figure 1 a. When a negative bias smaller than !0.3 V wasapplied to the Pt/SiC photocathode, a photocurrent was generated. When the (FAPbI3)0.85(MAPbBr3)0.15 perovskite solar cell
was used, the solar cell was irradiated with transmitted lightthrough the Pt/SiC photocathode. Upon using the solar cell,the onset bias drastically shifted toward positive from !0.3 to+ 0.3 V. The photoelectrochemical cell with the solar cellshowed a photocurrent under no additional bias conditions,giving a solar-to-hydrogen (STH) efficiency of 0.04 % calculated
from the photocurrent.
To improve the water splitting efficiency, the oxygenevolving anode was replaced with a CoOx-loaded BiVO4 dopedwith Mo (CoOx/BiVO4 :Mo) photoanode, as depicted in Figure 3 a. The CoOx/BiVO4 :Mo showed anodic photocurrents at
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Communications
was incorporated behind the Pt/SiC and CoOx/BiVO4 :Mo photoelectrodes, the open circuit voltage became 1.8 V owing to theassistance of the photovoltage (1.1 V). The STH efficiency was
dramatically improved from 0.04 % (Figure 2) to 0.55 % (Figure 3 c) under no additional bias conditions by employing the
CoOx/BiVO4 :Mo photoanode.
To test the stability and the Faradaic efficiency of thesystem, the time dependence of the photocurrent was alsomeasured under no additional bias conditions, as shown in
Figure 4. The evolved gases were analyzed using GC every

Figure 4. Photoelectrochemical H2 and O2 evolution using a two-electrodesystem consisting of a Pt/SiC photocathode (1.51 cm2) and a CoOx/BiVO4 :Mo
photoanode (1.08 cm2) with a (FAPbI3)0.85(MAPbBr3)0.15 perovskite solar cell.
The sum of the areas of the SiC photocathode and BiVO4 photoanode(2.59 cm2) was used for the calculation. Light source: solar simulator(AM 1.5G); electrolyte: aqueous borate buffer solution (pH 9.1). Layoutof the system is the same as Figure 3 a.

Figure 3. a) Layout of a two-electrode system with a Pt/SiC photocathodeand a CoOx/BiVO4 :Mo photoanode. b) Measured currents and c) STH
efficiencies using a two-electrode system with a Pt/SiC photocathode and a
CoOx/BiVO4 :Mo photoanode in the presence and absence of a
(FAPbI3)0.85(MAPbBr3)0.15 perovskite solar cell. Solid and dashed lines represent
the current under illumination and in the dark, respectively. The triangles
indicate onset bias of photocurrents. The sum of the areas of the SiC
photocathode and BiVO4 photoanode (2.59 cm2) was used for the calculation. Light source: solar simulator (AM 1.5G); electrolyte: aqueous borate
buffer solution (pH 9.1).

potentials higher than 0.3 V versus RHE,[47] giving an overlapped range between potentials for the anodic photocurrentof the CoOx/BiVO4 :Mo and the cathodic photocurrent of the
Pt/SiC (Figure S2). Accordingly, the two-electrode photoelectrochemical cell with the Pt/SiC photocathode and the CoOx/
BiVO4 :Mo photoanode showed a clear photocurrent without
assistance of external bias, giving a STH efficiency of 0.20 % calculated from the photocurrent (Figure 3 b, c). The open circuit
voltage was 0.8 V, which corresponded well to the width ofthe overlapped potential range (Figure S2). When the solar cell
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30 min. After a decrease in the photocurrent during the first
30 min from the start of photoirradiation, the decreasing rate
became relatively slow for at least 2.5 h. The fluctuating photocurrent is probably owed to the solar cell, because such unsteady photocurrent was not observed in the absence of thesolar cell (Figure S3). Moreover, stoichiometric H2 and O2
evolved under simulated sunlight irradiation. The actual rates
of gas evolution matched with the theoretical rates calculated
from the photocurrent measured. The almost 100 % Faradaic
efficiency indicates that the photocurrent was used for water
splitting.
In conclusion, a Pt/SiC photoelectrode was successfully usedas photocathode in a photoelectrochemical cell containing a
CoOx/BiVO4 :Mo photoanode. Although the Pt/SiC photoelectrode cannot reduce water to H2 without assistance of an external bias, photoelectrochemical water splitting under simulated sunlight (AM 1.5G) irradiation without assistance of an external bias was achieved upon combination with the CoOx/
BiVO4 :Mo photoanode. The photocurrent was further improvedby incorporating a (FAPbI3)0.85(MAPbBr3)0.15 perovskite solar cellthat efficiently utilized the transmitted light through the Pt/SiC
or CoOx/BiVO4 :Mo photoelectrodes.

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Acknowledgements
This work was supported by JSPS KAKENHI Grant Numbers
JP24107001, JP24107004 in Scientific Research on Innovative
Areas “All Nippon Artificial Photosynthesis Project for Living Earth(AnApple)”.

Conflict of interest
The authors declare no conflict of interest.
Keywords: bismuth vanadate · photocatalysis
carbide · sustainable chemistry · water splitting·

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Manuscript received: August 31, 2017
Accepted manuscript online: September 28, 2017
Version of record online: October 19, 20174423

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