Interfacial engineering of hematite photoanodes toward high water splitting performance

Abstract

Efficient and scalable photoelectrochemical water splitting electrode designs are a challenge. This study focuses on hafnium-modified hematite (X%Hf-HEM) photoanodes, prepared via spin-coating polymeric precursor solutions with varying Hf4+/Fe3+ (mol) ratios (1.0%, 3.0%, 4.0%, and 5.0%) onto fluorine-doped tin oxide substrates. Structural, morphological, and compositional analyses confirm pure hematite phases in all X%Hf-HEM samples. Increasing Hf4+ content correlated with reduced grain size, thickness, and surface roughness due to Hf4+ segregation at grain boundaries during thermal treatment. Hafnium segregation at hematite grain boundaries and hematite|fluorine-doped tin oxide interfaces is confirmed using scanning transmission electron microscopy coupled with energy dispersive spectroscopy. Notably, the 4%Hf-HEM photoanode exhibits exceptional efficiency enhancement, outperforming HEM efficiency by 4.5 times. Gas chromatography results highlight O2 and H2 evolution rates of 14.49 ± 0.09 μmol/cm2/h and 8.1 ± 0.5 μmol/cm2/h, respectively, for 4%Hf-HEM, with a H2/O2 ratio close to 2:1. The charge dynamics investigated from intensity-modulated photocurrent spectroscopy evidence the main Hf4+ effect of improving charge separation, achieving greater efficiency for 4%Hf-HEM. Shifts in valence band maximum from ultraviolet photoelectron spectroscopy measurements indicate surface state presence, supported by ηtransfer trends calculated from intensity-modulated photocurrent spectroscopy. This research presents a scalable, cost-effective approach to multiinterface photoanode development, holding promise for innovative photoelectrochemical water splitting technologies.