Low-energy-consumption electrochemical CO2 reduction coupled with SO2 electrooxidation using bifunctional Ni-N-C electrocatalysts

In traditional CO 2 electrolysis systems, oxygen evolution reaction (OER) consumes 90 % of the electricity input, whereas the product of oxygen holds minimal value. Moreover, the use of different electrocatalysts for the anode and cathode remains a challenge due to high capital costs of the electrolysis system. Substituting the OER with thermodynamically advantageous value-added anodic reactions and developing bifunctional electrocatalysts are crucial for the advancement of CO 2 electrolysis. In this study, for the first time, we present an innovative CO 2 electrolysis system that integrates CO 2 electroreduction reaction (CO 2 RR) with SO 2 electrooxidation reaction (SO 2 OR) and employ Ni-N-C as the bifunctional electrocatalysts to produce CO and H 2 SO 4 simultaneously. Notably, the novel CO 2 electrolysis system can reduce the cell voltage by 1.05 V, resulting in nearly 50 % reduction in energy consumption. This is also the first attempt to use Ni-N-C to catalyze SO 2 OR, showing markedly superior performance compared to commercial 20 % Pt/C. In-situ ATR-SEIRAS and DFT calculations demonstrate that the NiN 4 sites in Ni-N-C catalysts augment the direct conversion of *SO 2 to *HSO 4 - , identified as the rate-determining step for the SO 2 OR. This work provides guidance for the design of novel CO 2 electrolysis systems, the construction of bifunctional electrocatalysts, as well as the mechanistic investigation of the SO 2 OR.