The electrocatalytic activity of the electrodes for HER was studied in a common three-electrode cell containing 1.0 M KOH(aq) electrolyte. Graphite and mercury oxide/mercury (HgO/Hg) were used as counter current and reference electrodes respectively (details in SI: electrochemical evaluation section). The properties of the CoxB-[0.2]P-O as active catalyst coating were determined from comparative iR-corrected linear sweep voltammetry (LSV) curves. The LSV curve of CoxB-[0.2]P-O shows a significant shift toward lower potentials compared to that of both the NF substrate and even a commercial 20% Pt/C catalyst loaded on the NF (Fig. ).