Electrolyte effects on undoped and Mo-doped BiVO4 film for photoelectrochemical water splitting

As the electrolyte in a photoelectrochemical system used for solar water splitting is closely associated with the charge transfer phenomenon, the fundamental study of the electrolyte is an increasingly crucial issue. In this paper, the relation between the photoelectrochemical performance and the variation of electrolyte composition is investigated in depth. Here, the potassium phosphate (KPi) containing different anions (CH3COO-, Cl- and NO2-) or cations (NH4+, K+ and Na+) was prepared at the electrolyte with the different pH values of 5, 7, 9, and 11 in order to investigate how anions or cations affect the PEC performance. Herein, we compared the differences in the undoped and Mo-doped BiVO4 films due to the different bulk/surface states, and found different morphological and crystalline features as well as remarkably different PEC performance. At first, the pH in the electrolyte significantly influences the solar water oxidation reaction, revealing that the electrolyte with a high pH grants better PEC activity, because the higher pH solution can provide more hydroxide ions (OH-) to react with holes to form hydroxyl radicals, which are recognized as important intermediates for PEC water oxidation in the presence of O-2. Further, in the electrolyte containing the different cations, the NH4+ ions exhibit the enhanced PEC performance, due to its cation size which increases the ionic dissociation and viscosity. By contrast, the anion effect can be negligible in the used electrolyte. From this fundamental research, it can be known that the optimization of electrolyte is quite a vital parameter for advancing the PEC performance.