American Chemical Society
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Enhancing Photoelectrochemical Water Oxidation Efficiency of BiVO4 Photoanodes by a Hybrid Structure of Layered Double Hydroxide and Graphene

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journal contribution
posted on 2017-08-29, 00:00 authored by Xin Zhang, Ruirui Wang, Fan Li, Zhe An, Min Pu, Xu Xiang
Making solar fuels, e.g., hydrogen from water splitting, is one of the most critical pathways to developing a clean energy economy. The overall water splitting includes two half-reactions, i.e., water reduction and water oxidation, in which the latter is a speed-limiting step because of its multiproton-coupled four-electron process. It is highly desirable to improve the efficiency of the prevailing photoelectrochemical (PEC) anodes. We constructed an integrated BiVO4 photoanode modified with a hybrid structure of CoAl-layered double hydroxides (LDHs) and graphene (G), i.e., G@LDH@BiVO4. This triadic photoanode exhibited a remarkably enhanced performance toward PEC water oxidation, compared to LDH@BiVO4 and pristine BiVO4. The photocurrent density of G@LDH@BiVO4 achieved 2.13 mA·cm–2 (at 1.23 V vs reversible hydrogen electrode, RHE), 4 times higher than that of pristine BiVO4. The oxidation efficiency is as high as 80% even at a low bias (<0.8 V vs RHE). The incident photon-to-current conversion efficiency (IPCE) of G@LDH@BiVO4 reaches 52% at 400 nm, 2.5 times higher than that of BiVO4. The photoconversion efficiency peaked at 0.55% at a bias of 0.72 V, a 25-fold increase over that of BiVO4. The findings indicated that the improvement of charge separation efficiency is mainly ascribed to graphene. The enhanced charge transfer efficiency is a consequence of the synergy of graphene and an LDH, where the LDH is capable of expediting water oxidation kinetics and graphene promotes photogenerated charge transfer.