Photocatalytic reaction using powder-form semiconductor has widely investigated for potential industrial application, but fundamental understanding using quantitative parameterss is largely lacking partially because no effective characterization tools are available. The present work compares the oxygen evolution reaction (OER) in electrocatalysis and photocatalysis in aqueous solutions using nanostructured NiFeO_x as catalysts. The electrocatalytic study can rigorously measure and compare kinetics of different catalysts, where, e.g., potential as the variable and current as a recording signal. In this study, we used the same catalysts but varied the reaction conditions (pH and reaction temperature) and monitored how the electrocatalytic and photocatalytic OER kinetics were affected. For electrocatalysis, hydrothermally decorated a NiFeO_x catalyst on Ni foam was used. In 1 M KOH solution, high OER performance of the NiFeO_x electrocatalyst was reconfirmed, achieving 10 mA cm⁻² at an overpotential of 260 mV. For photocatalysis, the same catalyst was decorated on the surface of Ta₃N₅ photocatalyst powder. The reaction was conducted in the presence of 0.1 M Na₂S₂O₈ as a strong electron scavenger,thus likely leading to the OER being kinetically relevant. The NiFeO_x/Ta₃N₅ photocatalyst demonstrated a quantum efficiency of 24% at 480 nm. A strong correlation between the electrocatalytic and photocatalytic performances was identified: an improvement in electrocatalysis corresponded with an improvement in photocatalysis without altering the identity of the materials. The rate change at different pH was likely associated with electrocatalytic kinetics that accordingly influenced the photocatalytic rates. The sensitivity of the reaction rates with respect to the reaction temperature resulted in an apparent activation energy of 25 kJ mol⁻¹ in electrocatalysis, whereas the apparent activation energy in photocatalysis was 16 kJ mol⁻¹. The origin of the difference in these activation energy values is likely attributed to the possible effects of temperature on the individual thermodynamic and kinetic parameters of the reaction process. The work described herein demonstrates a method of “transferring the knowledge of electrocatalysis to photocatalysis” as a strong tool to rationally and quantitatively understand the complex reaction schemes involved in photocatalytic reactions.