Fig. 4: Photoelectrochemical performance.

a J–V curves, b extracted V_on, c chopped J–V curves, d local enlarged chopped J–V curves, e surface charge separation, f bulk charge separation, g ABPE, h IPCE, and i OCP-derived carrier lifetimes for Ta:Fe₂O₃, Ta:Fe₂O₃@Fe₂O₃, and NiFe(OH)_x/Ta:Fe₂O₃@Fe₂O₃ photoanodes.