Charge separation at BiVO4/Co3O4 and BiVO4/CoOOH interfaces: Differences between dense and permeable cocatalysts

A CoOOH cocatalyst overlayer is electrochemically deposited on the BiVO4 surface, and thermal annealing converted CoOOH to Co3O4 in situ. The primary difference between the two cocatalysts lies in their electrolyte permeabilities, resulting in significant differences in their thermodynamic effects on enhancing the photoelectrochemical water oxidation performance. We proved that the CoOOH cocatalyst is unable to achieve true chemical passivation of the surface states of the BiVO4 photoanode, whereas the Co3O4 cocatalyst can chemically passivate the surface states. Nevertheless, the CoOOH cocatalyst still exhibits better water oxidation performance than Co3O4, which is attributed to the fact that the permeable CoOOH cocatalyst can accumulate more photogenerated holes in the bulk phase and provide more active sites. However, the CoOOH cocatalyst still exhibits better water oxidation performance compared to Co3O4, which is attributed to the permeable CoOOH cocatalyst can accumulate more photogenerated holes in its bulk phase and offer more active sites. [Display omitted] •A CoOOH cocatalyst overlayer on BiVO4 photoanode is converted to Co3O4 in situ.•We experimentally demonstrate the CoOOH cocatalyst is unable to achieve true chemical passivation of the surface states.•We experimentally demonstrate that CoOOH could accumulate more holes and generate a larger photovoltage compared with Co3O4. A CoOOH cocatalyst overlayer is electrochemically deposited on the BiVO4 surface, and thermal annealing converted CoOOH to Co3O4 in situ. The primary difference between the two cocatalysts lies in their electrolyte permeabilities, resulting in significant differences in their thermodynamic effects on enhancing the photoelectrochemical water oxidation performance. We proved that the CoOOH cocatalyst is unable to achieve true chemical passivation of the surface states of the BiVO4 photoanode, whereas the Co3O4 cocatalyst can chemically passivate the surface states. Nevertheless, the CoOOH cocatalyst still exhibits better water oxidation performance than Co3O4, which is attributed to the fact that the permeable CoOOH cocatalyst can accumulate more photogenerated holes in the bulk phase and provide more active sites. However, the CoOOH cocatalyst still exhibits better water oxidation performance compared to Co3O4, which is attributed to the permeable CoOOH cocatalyst can accumulate more photogenerated holes in its bulk phase and offer more active sites.