To investigate the electrocatalytic

To investigate the electrocatalytic activity and kinetics of NO3- reduction, we tested each catalyst on rotating disk electrodes (RDEs). With the Cu50Ni50 catalyst, we found an onset potential of ~0.25 V vs RHE (pH = 14) for NO3- reduction (Fig. 2a). The current density then increased sharply to its transport-limited ceiling of ~170 mA cm-2 (according to equation 1 in Supporting information) at 100 rpm in 1 M KOH + 100 mM KNO3 (pH = 14) electrolyte. On the pure Cu catalysts, we found that a much more negative cathodic potential was required to reach this same NO3--transport-limited current: the current density was only 100 mA cm-2 at -0.2 V vs. RHE which was only 60% of that obtained by operating the Cu50Ni50 catalyst at the same potential. The pure Ni catalyst is almost inactive for NO3- reduction (Fig. S8a and b