Electrolyte Effects in Ni–N–C Single-Metal-Site-Catalyzed Electrochemical CO ₂ Reduction

High Resolution Image Download MS PowerPoint Slide The catalytic performance of the electrochemical CO 2 reduction reaction (CO 2 RR) is highly sensitive to the electrolyte microenvironment, including ion identity, concentration, and buffering chemistry. While such electrolyte effects are well established for metallic catalysts, their mechanistic roles in porous Ni–N–C systems remain less explored. Here, we systematically investigate the influence of cation (Li +, K +, Cs +, and tetramethylammonium, TMA + ) and anion (phosphate, sulfate, and bicarbonate) identity and concentration on CO 2 -to-CO conversion. Contrary to expectations, Cs + does not outperform K +, whereas TMAHCO 3 electrolytes exhibit a pronounced enhancement in CO 2 RR activity, reaching a CO partial current density of 25 mA cm –2 at –0.7 V RHE in 0.5 M solution. Electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) analysis reveal that this activity enhancement does not directly correlate with interfacial ion-/charge-transfer or mass transport behaviors. Instead, Fourier-transform infrared (FTIR) spectroscopy shows a significant increase in bulk CO 2 availability in TMAHCO 3 electrolytes. Overall, these results suggest that electrolyte composition affects both interfacial properties and CO 2 availability in the bulk, influencing CO 2 RR activity within the porous Ni–N–C catalyst system.