What it is
Using Sn doping to tune the band-bending profile of an Fe2O3 photoanode, the authors separate the roles of space charge layer width and built-in electric field in the charge dynamics of photoelectrochemical water splitting, probed by in-situ time-resolved spectroscopies. They find that the space charge layer width sets the onset of photogenerated charge separation, with a threshold of about 2.4 nm. Above that width, the strong built-in electric field empties occupied electron trap states and blocks recombination between back electrons and charged intermediates, promoting the surface hole accumulation that raises the water oxidation rate.
Why it matters
Photoelectrochemical water splitting is a candidate route to renewable solar fuel, and its efficiency hinges on charge separation within the space charge layer, yet how the built-in electric field and the layer width each govern that separation had remained unclear. By disentangling the two contributions experimentally, this work assigns each a distinct role: the width sets when charge separation begins (a threshold near 2.4 nm), while the field suppresses recombination. That separation gives a clearer target for engineering more efficient photoanodes.
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Filed underIron oxide chemistry and applications, TiO2 Photocatalysis and Solar Cells, Ammonia Synthesis and Nitrogen Reduction