We have investigated the NO3RR on a series of polycrystalline TM foils in neutral, buffered (0. Ed approaches EF, commensurate with increasing ammonium selectivity, reaching a maximum for Co. However, selectivity decreases for Fe, attributed to reduced driving force for nitrite reduction to nitric oxide. These results identify competing design considerations -linking electronic structure to mechanistic selectivity-limiting steps -offering strategies to improve existing catalysts and design new alloy compositions for NO3RR to ammonium.