Selectivity (Eqn. 2) towards nitrite trends higher with nitrate concentration for both Cu/CeO2-δ-C and Cu/C-Felt (Figure ), also supporting a competitive adsorption mechanism. Increased nitrate coverage with concentration displaces adsorbed hydrogen, favoring the production of less-reduced intermediates (e.g. nitrite) over hydrogenated products (e.g. ammonium) at the low 0.2 e -/NO3 -passed here. This may also be caused by nitrite having a coverage-dependent adsorption energy, becoming less stable at greater coverages and desorbing before being able to reduce further. ΔNTot, quantized by changes in total nitrogen, is negligible at all potentials and conversions investigated here (Figure ), similar to observations made at low conversion in the low concentration regime (< 4 e -/NO3 -, Figure and S16). This observation further supports that ΔNTot at neutral pH occurs only in the presence of appreciable aqueous-phase nitrite concentration. FE towards ammonium generally increases with increasingly cathodic potentials for both supported materials (Figure ), though is consistently lower for Cu/CeO2-δ (Figure ).