ABSTRACT: Heterogeneous photocatalysis is a potentially competitive solution for the direct production of solar fuels. Methods of determining photonic efficiency in heterogeneous photocatalysis should be rigorously applied to determine the accurate photonic efficiency for comparison. Generally, photocatalytic activity for water splitting in the form of powder suspension is compared only by measuring gaseous products. One approach to pin down quantitative descriptors of photocatalytic materials is to utilize knowledge of electrocatalysis. Such successful cases include a comparison of the oxygen evolution reaction (OER) in electrocatalysis and photocatalysis using NiFeOx as a catalyst. NiFeOx was an excellent electrocatalyst where in 1 M KOH solution achieved 10 mA cm−2 at an overpotential of 260 mV. Decorating NiFeOx on Ta3N5 photocatalyst demonstrated a 5-fold improvement in photocatalytic oxygen evolution half reaction under visible light irradiation, achieving a quantum efficiency of 24% at 480 nm. The impacts of pH and reaction temperature in both systems on OER kinetics were consistent with the electrocatalysis and photocatalysis. Transferring the knowledge of electrocatalysis to photocatalysis proves to be a viable method to quantitatively understand the complex reaction schemes involved in photocatalytic reactions.