One Stone Three Birds: An Aqueous Mg-CO2 Battery for Generation of Electricity, Syngas, and High-Value Phosphate

Mg-CO2 battery as a promising strategy for CO2 conversion and utilization is challenging, owing to the sluggish kinetics of CO2 reduction reaction (CO2RR) and the waste of the sacrificial Mg anode. Herein, by elaborately designing a highly selective Ni NPs/Ni-N-C SACs electrocatalyst toward CO2RR and rationally optimizing the electrolyte, an effective aqueous-phase Mg-CO2 battery is demonstrated to generate not only electricity, but also syngas with CO from the CO2RR and H2 from the chemical oxidation of Mg, together with higher-valued MgHPO4 phosphate. Notably, the output of electricity, the proportion of CO/H2 in syngas, and the yields/crystalline quality of MgHPO4 can be well regulated by manipulating the operation parameters. The Mg-CO2 battery generates a favorable open-circuit voltage of 1.44 V with a peak power density of 2.91 mW cm-2. Under the optimal condition, the Ni NPs/Ni-N-C SACs catalyst displays both a high FECO of 98.12% at -0.573 VRHE and a high CO2-to-CO current of -20.73 mA cm-2 at -0.973 VRHE, owing to the synergistic effect between Ni particles and Ni-N moieties. The proposed Mg-CO2 battery provides an intriguing approach for CO2 conversion and utilization in off-grid, with the advantage of coproduction of higher-valued chemicals at both electrodes.