AbstractAchieving highly performant photoanodes for oxygen evolution is key to developing photoelectrochemical devices for solar water splitting. In this work, BiVO₄ photoanodes are enhanced with a series of core–shell structured bimetallic nickel‐cobalt phosphides (MPs), and key insights into the role of co‐catalysts are provided. The best BiVO₄/Ni_1.5Co_0.5P and BiVO₄/Ni_0.5Co_1.5P photoanodes achieve a 3.5‐fold increase in photocurrent compared with bare BiVO₄. It is discovered that this enhanced performance arises from a synergy between work function, catalytic activity, and capacitive ability of the MPs. Distribution of relaxation times analysis reveals that the contact between the MPs, BiVO₄, and the electrolyte gives rise to three routes for hole injection into the electrolyte, all of which are significantly improved by the presence of a second metal cation in the co‐catalyst. Kinetic studies demonstrate that the significantly improved interfacial charge injection is due to a lower charge‐transfer resistance, enhanced oxygen‐evolution reaction kinetics, and larger surface hole concentrations, providing deeper insights into the carrier dynamics in these photoanode/co‐catalyst systems for their rational design.