Boosting Photoelectrochemical Water Oxidation of Hematite in Acidic Electrolytes by Surface State Modification

State-of-the-art water-oxidation catalysts (WOCs) in acidic electrolytes usually contain expensive noble metals such as ruthenium and iridium. However, they too expensive to be implemented broadly in semiconductor photoanodes for photoelectrochemical (PEC) water splitting devices. Here, an Earth-abundant CoFe Prussian blue analogue (CoFe-PBA) is incorporated with core–shell Fe2O3/Fe2TiO5 type II heterojunction nanowires as composite photoanodes for PEC water splitting. Those deliver a high photocurrent of 1.25 mA cm−2 at 1.23 V versus reversible reference electrode in acidic electrolytes (pH = 1). The enhancement arises from the synergic behavior between the successive decoration of the hematite surface with nanolayers of Fe2TiO5 and then, CoFe-PBA. The underlying physical mechanism of performance enhancement through formation of the Fe2O3/Fe2TiO5/ CoFe-PBA heterostructure reveals that the surface states’ electronic levels of hematite are modified such that an interfacial charge transfer becomes kinetically favorable. These findings open new pathways for the future design of cheap and efficient hematite-based photoanodes in acidic electrolytes.
This work was supported by the Spanish Ministerio de Economia y Competitividad (MINECO, Grants CTQ2015-71287-R, CTQ2015-71287-R, and CTQ2015-68770-R) and the coordinated Project ValPEC (ENE2017-85087-C3), the BIST Ignite Project inWOC2 and the Generalitat de Catalunya (2017 SGR 90, 2017 SGR 327, 2017 SGR 329, 2017 SGR 1246, and 2017 SGR 1406). ICN2 acknowledges the support from the Severo Ochoa Program (MINECO, Grant SEV-2017-0706). ICN2, ICIQ, and IREC are funded by the CERCA Programme/Generalitat de Catalunya. P.Y.T. acknowledges the scholarship support of DAAD short term grant. H.C.D. acknowledges support from the Deutsche Forschungsgemeinschaft (SFB 917). F.S.H. thanks the “LaCaixa”-Severo Ochoa International Programme (Programa internacional de Becas “LaCaixa”- Severo Ochoa) for a Ph.D. fellowship. P.P. and M.H. thank for the support by the Federal Ministry for Economic Affairs and Energy (BMWi) (Fundingregistration number: 03ET6080E). M.L. thanks the COST Action StableNextSol project MP1307, supported by COST (European Cooperation in Science and Technology). H.X. acknowledges the Spanish MINECO through the Severo Ochoa Centers of Excellence Program under Grant SEV-2013-0295 for the postdoctoral contract.