Fig. 3: Electrochemical activation, selectivity, and activity for the NO3RR and NO2RR.
a Example of a linear sweep voltammetry (LSV) curve for the Cr-N-C catalyst in electrolytes of 0.05 M PBS (HER), 0.05 M PBS + 0.01 M KNO2 (NO2RR) and 0.05 M PBS + 0.16 M KNO3 (NO3RR). Representative LSV over the metal free N-C and a variety of 3d and 4d metals for the (b) NO3RR and (c) NO2RR. Complete LSV for all examined M-N-C and metal free catalysts are given in Fig. S28. d Gap analysis plot (GAP) for the electrochemical NO3RR for all M-N-C catalysts in 0.05 M PBS + 0.16 M KNO3 for 2 h. The top section of the figure shows the Faradaic efficiency for NO2− (blue; top-down) and NH3 (gray; bottom-up) as a function of the applied potentials between −0.2 V and −0.8 V vs. RHE. A horizontal line is set at 50% FE to guide the eye. The bottom section of the figure shows the corresponding yield rate (μmol h−1 cm−2) for NO2− (blue; triangle) and NH3 (gray; circle) as a function of the applied potentials. The corresponding NO3RR chronoamperometry plots and UV–Vis detection for NO2− and NH3 concentrations are shown in Figs. S29–38. Error bars are determined from three replicate trials at −0.40 V vs. RHE. The GAP for the metal free N-C catalysts is shown in Fig. S39.
