For TMs binding H * weakly (Figure ), nitrate rate order exhibits a potential-dependent peak (Figure ), reminiscent of a competitive Langmuir-Hinshelwood mechanism. We therefore hypothesize that this peak shape originates from competitive adsorption between H * and nitrate. Increasing H chemisorption energy corresponds to a decreased peak rate order magnitude and shift to less-cathodic potentials. These experimental rate-order profiles are welldescribed by our microkinetic model (Figure ), assuming reduction of adsorbed nitrate to nitrite is rate limiting (via sequential PCET and/or hydrogenation, Supplementary equations 19-21) and describing HER kinetics (Supplementary equations 7-15) following the work of Shinagawa et al. Agreement between experimental (Figure ) and modeled (Figure ) nitrate rate order versus potential can be achieved by changing only the thermodynamic parameters reflecting the difference in Δ𝐺 𝐻 Δ𝐺 𝑁𝑂 ), rate order magnitude increases (Figure ) due to the exponential dependence of nitrate reduction on overpotential (Supplementary equations 19-21, Supplementary Figure ). This provides a physical interpretation of why Δ𝐺 𝐻 Δ𝐺 𝑁𝑂 3 -dictates both Emax rate and rate order magnitude, while the ratio of kinetic parameters (reaction rate constants; kNO3RR:kHER) only controls magnitude (Supplementary Figure ).