NO3RR FE and selectivity were also measured at a series of potentials at a fixed 0.2 e -/NO3 -in stirred 0.05 M NaxH3-xPO4 with 0.05 M NaNO3 (Figure ). Similar to nitrate reduction at low concentration and conversion (Figure ), the primary reduction product observed at higher nitrate concentrations (50 mM) and low conversion (ca. <10% for all potentials considered here, Figure ) is nitrite. In contrast, higher nitrate concentrations increase NO3RR FE and nitrate conversion relative to low nitrate concentrations (Figure ).