Accumulation of Positive Charges Induces an Efficiency Bottleneck in BiVO₄ Photoanodes for Water Splitting

The oxygen evolution reaction represents the primary kinetic bottleneck in photoelectrochemical water splitting and typically necessitates an external bias. The fundamental impact of charge accumulation induced by applied overpotential remains insufficiently understood. This work identified that the excess accumulation of surface-positive charges on BiVO₄ photoanodes acts as a detrimental kinetic barrier that impedes water oxidation. The construction of a NiO-BiVO₄ p-n junction could facilitate electron migration toward the photoanode surface to effectively neutralize excess positive charge and modulate the polarizability of V-O bonds. In situ Raman spectra reveal the formation of high-valent Ni⁴⁺ species within NiOOH⁺ stabilized the V-O bond polarizability. Consequently, the photoanode achieved a photocurrent density of 6.48 mA cm^-2 at 1.23 V_RHE. This work revealed that rational regulation of interfacial charge density via p-n junction engineering was critical for stabilizing key bond polarizabilities, providing a general strategy to overcome kinetic limitations in solar energy conversion.