The current density, normalized to

The current density, normalized to the electrochemically active surface area (ECSA)， increases exponentially to ~1 mA cm-2 along with the cathodic potential for the case of Cu50Ni50. In contrast, an evident multi-electron transfer process (Fig. 2a and b) was seen on the pure Cu catalyst. Cu50Ni50 catalysts exhibited a 40% lower ECSA, determined by its double-layer capacitance, compared to pure Cu (Fig. S9a-c). This translated to a 6-fold increase in ECSA- normalized current density for Cu50Ni50, compared to pure Cu at 0 V vs. RHE (Fig. 2b). The intrinsic NO3-RR activity was significantly improved using the CuNi alloy systems.