Understanding the material-dependent driving force for nitrite (the predominant NO3RR side-product in neutral and alkaline electrolytes) reduction may shed further light on trends in ammonium selectivity. We next compare the calculated free energy difference between nitrite and nitric oxide (Δ(𝐺 𝑁𝑂 𝐺 𝑁𝑂 2 -), Figure circles). Deoxygenation is assumed to occur by PCET common across all catalysts and is treated here by including ½ O2 as a product in the reaction free energy difference; i.e. NO2 -* → NO * + ½ O2. The free energy of nitrite adsorption (Δ𝐺 𝑁𝑂 2 -) scales with both that of associative (Δ𝐺 𝑁𝑂 ) and dissociative (Δ𝐺 𝑁 +𝑂 ) nitric oxide adsorption (Supplementary Figure ), in-line with scaling relationship for molecules of similar functionality. As Ed approaches EF, Δ(𝐺 𝑁𝑂 𝐺 𝑁𝑂 2 -) becomes increasingly negative up to Ni, then increases for Co and Fe. Assuming the BEP relationship holds for electrochemical reduction of nitrite to nitric oxide, a more negative Δ(𝐺 𝑁𝑂 𝐺 𝑁𝑂 2 -) would then correspond to a lower activation barrier, increasing the preference towards nitrite reduction to nitric oxide (and possibly further to ammonium) over desorption.