Paired electrolysis for efficient coproduction of CO and S₈ with techno-economic analysis

Abstract

Electrochemical CO<inf>2</inf> reduction (CO<inf>2</inf>RR) to carbon monoxide (CO) offers significant economic and commercial potential. However, industrial-scale implementation of CO<inf>2</inf>RR for CO is presently impeded by high energy consumption, e.g., cell voltage >2.0 V at currents densities of 100 mA cm−2, due to the low efficiency of existing catalysts, the high potential required for the anode reaction and the electrode/cell design. Herein, we developed a biomimetic bifunctional catalyst consisting of cobalt polyphthalocyanine-coated porous nitrogen-doped carbon aerogels (CoPPc/PNCA), featuring with a “coral-like” structure and stable single-molecular sites, which could drive CO<inf>2</inf>RR coupling with electrochemical sulfur oxidation reaction (SOR). Applied in the self-designed cathode gas electrode (CGE), the bifunctional catalyst achieves nearly 100 % Faradaic efficiency for CO production, and the stable SOR operation at the current density of ∼100 mA cm−2 in traditional H-cell. Furthermore, a CGE/flow membrane electrode assembly (CGE/FMA) electrolyzer was constructed with CoPPc/PNCA as the cathode and anode catalyst, achieving the industrial-level CO current density of 210 ± 16 mA cm−2 in an energy-saving CO<inf>2</inf>RR//SOR system at a cell voltage of −1.8 V, significantly reducing the energy consumption. Techno-economic analysis based on the CO<inf>2</inf>RR//SOR coupling system indicates profitability with the production cost of CO estimated to be $0.204 kg−1 at ∼110 mA cm−2.