Successful operation of an alkaline water electrolyzer involves more than simply employing the best half-cell for each reaction separately, as an efficient electrode requires the combination of active reaction sites, effective charge transfer, acceptable price and low potential difference between the two electrodes. In order to improve the descriptor-based selection criteria for trimetallic Cu-Co-Mo heterostructures, this work takes into account CuCoMo-LDH, CuCoMo-P and CuCoMo-S electrodes as complete systems, not individual oxygen evolution and hydrogen evolution catalysts. The calculation is made based on experimental values of surface area, impedance, overpotential, potential difference, Faradaic efficiency and electrode price in order to create the impedance-normalized operating window method. CuCoMo-P demonstrates the highest performance, possessing the greatest BET surface area (21.35 m2 g−1), the largest ECSA (440 cm2), the smallest charge-transfer resistance during HER (1.61 Ω), the smallest potential difference during electrolysis at 10 mA cm−2(1.393 V) and the lowest energy intensity per 1000 L of produced hydrogen, approximately equal to 3.33 kW h. CuCoMo-LDH is still the best catalyst for OER reaction at the 50 mA cm−2 current density, however, the difference in OER overpotentials is much lower than the difference in HER overpotentials and the difference in the potential difference.
