In this work, we investigate the effect of external bias potential on the photodynamics of a NiObased photocathode in phosphate buffer solution (PBS) by time-resolved photoluminescence phenyl-amino)-benzoicacid], especially designed for the functionalization of p-type semiconductors. We observe that both light-induced hole injection from P1 into the NiO and charge recombination strongly depend on the applied external potential, and assign the trends observed to a change in ions in the inner Helmholtz plane (IHP) of the electrochemical double layer. Our work demonstrates the important role of bias dependent ion adsorption in the electrochemical double layer on the interface photodynamics during operation. Figure shows the UV-Vis absorbance spectra of the NiO film in PBS (pH = 7, the commonly used electrolyte) at various applied negative potentials from 0 V to -0.9 V. Clearly the spectra are very similar, indicating that reduction of Ni 2+ to Ni is minor or negligible in this potential range.