, where E RHE represents the potential of RHE. The reference electrode, Ag/AgCl, has a standard electrode potential (E Ag/AgCl ) of 0.197 V and the overpotential (η) can be determined using η = E vs.RHE -E theoretical , where the theoretical potentials for OER and HER relative to RHE are 1.23 V and 0 V, respectively. To ensure accurate potential measurements, the reference electrode was calibrated to the RHE scale in a high-purity hydrogen-saturated 1 M KOH electrolyte and using a platinum plate as both the working and counter electrode. Slow scan (1 mV s -1 ) cyclic voltammetry (CV) was performed to identify the thermodynamic hydrogen electrode potential as the average of the two zero-current potentials (Figure ). In 1 M KOH, E RHE = E Ag/AgCl + 1.005 V.