Hematite photoanodes were prepared by anodic electrodeposition in the presence of polyvinylpyrrolidone (PVP). PVP has been shown to alter hematite nanoparticle morphology, but has not been used before for anodic electrodeposition of thin films. Significant improvement in the water oxidation photocurrent was observed with PVP, with greater charge-collection efficiency due to a finer nanostructured morphology, and higher quantum yields for photons absorbed throughout the thickness of the hematite film from its increased porosity. Different post-deposition treatments showed distinct effects with and without PVP. Compared to electrodes dried 48 hours before annealing under N 2 , electrode performance was significantly reduced upon annealing in air, or annealing immediately after deposition when PVP was not used. A distinct wavelength dependence for front-versus back-side illumination, and a ∼100-fold decrease in dopant density, was attributed to formation of a dead layer on the top of those electrodes with reduced photoactivity, and was avoided using PVP. The stability, abundance, and environmental compatibility of hematite (α-Fe 2 O 3 ) make it an attractive candidate for realizing the goal of directly generating hydrogen gas from water and sunlight with high efficiency and at low cost. Hematite is stable in all but acidic solutions, can absorb ∼40% of the solar spectrum, and has suitable band edge positions for water oxidation. However, its performance in photoelectrochemical (PEC) cells is plagued by its short holediffusion lengths. To overcome this, electrodes with nanostructured morphologies are commonly prepared to optimize photon absorption and charge-carrier collection.1-3 High aspect-ratio nanorods or other nanostructures allow for the orthogonalization of the absorption depth and charge-carrier-diffusion length, which is on the order of 2-10 nm for hematite. 4,5 In addition, modification of the surface with catalysts has been shown to reduce overpotentials by improving water oxidation kinetics and/or reducing surface recombination rates.1,6-10 Other studies have focused on doping hematite to alter charge-carrier densities, increase conductivity, and/or increase charge separation, transport, and collection efficiency. 2,3,[11][12][13][14][15] Although these efforts have led to impressive gains in performance, conversion efficiencies remain well below the theoretically predicted maximum value and many questions remain about how to maximize charge-carrier generation and collection, and how to optimize interfacial electron-transfer kinetics for the sluggish oxygen evolution reaction.Hematite thin films can be grown by a variety of methods, including atomic layer deposition, 7,15-17 hydrothermal precipitation, 3,18 spray pyrolysis, 19,20 chemical vapor deposition, 1,6,21 and electrodeposition, 22-26 among others. Electrodeposition provides a relatively simple, flexible, low-cost and easily scalable approach to synthesizing hematite. In this report, we focus on anodic electrodeposition to fabricate hematite phot...
