NO3RR FE and selectivity are first considered here at nitrate concentrations that might be typical of groundwater exceeding EPA drinking water standards. Selectivity measurements in stirred 0.05 M NaxH3-xPO4 with 1.6 mM NaNO3 (22.6 ppm NO3 --N, added nitrate) were measured by CA (-0.4 VRHE) at increasing amounts of e -/NO3 -(Figure ). We note that initial nitrate, measured experimentally at the beginning of each experiment, includes added nitrate and any residual from electrodeposition of Cu and CeO2-δ on C-Felt electrodes. C-Felt is chosen as an analog to FTO, where neither substrate is expected to form 𝑣 𝑂 •• under the conditions investigated here.