Disentangling the effect of space and electric field on photoelectrochemical water splitting

Photoelectrochemical water splitting is a promising pathway for renewable solar fuel production. The photoelectrochemical performance strongly depends on the charge separation ability within the space charge layer. In space charge layer, the charge dynamics should be governed by band bending profile consisting with built-in electric field and space charge layer width, yet the precise mechanisms remain unclear. Herein, using Sn doping to regulate band bending profile of Fe2O3 photoanode, we disentangle the effect of space charge layer width and built-in electric field on charge dynamics in photoelectrochemical water splitting by in-situ time-resolved spectroscopies. Space charge layer width determines the onset of photogenerated charge separation, exhibiting a threshold of ~2.4 nm. Above WSCL threshold, the strong built-in electric field in Fe2O3 photoanode effectively empties the occupied electron trap states and blocks the recombination between the back electrons and charged intermediates, thereby facilitating surface hole accumulation for improving water oxidation reaction rate. Photoelectrochemical performance strongly depends on charge separation within space charge layer, but the precise mechanisms remain unclear. Here, the authors disentangle the effect of space charge layer width and built-in electric field on charge dynamics using in-situ time-resolved techniques.