Electrochemical co-upgrading CO2 and glycerol for selective formate production with 190% overall Faradaic efficiency

The overall energy efficiency (EE) is critical for commercializing promising electrochemical technologies, such as the carbon dioxide reduction reaction (CO2RR). Despite the rapid development of advanced catalysts and reactors for CO2RR, its commercial potential is still hindered by the sluggish oxygen evolution reaction (OER), which causes high cell voltages and low EEs. Herein, we developed a NiOOH@Ni3S2 catalyst on the surface of nickel foam (NF) via an electrochemical surface reconstruction strategy. We observed that the oxidation of glycerol (GLY) to formate (FA) is more thermodynamically favorable than the OER on the developed NiOOH@Ni3S2/NF catalysts. The Ni2+/Ni3+ redox couples within the NiOOH@Ni3S2 heterojunction enhance the charge transfer kinetics between the active sites and adsorbed reaction intermediates, facilitating the highly selective and active generation of FA from GLY oxidation reaction (GOR), with a remarkable Faradaic efficiency (FE) of 94% achieved at 100 mA·cm−2. Comprehensive mechanistic studies identified that the reaction pathway towards FA generation starts from glyceraldehyde intermediates, and glycolate was considered as the key species. Moreover, benefiting from the efficient conversion of CO2 to FA on bismuth nanosheets, the GOR//CO2RR paired electrolysis system realizes a remarkable overall FE of ca. 190% for FA co-production at 160 mA·cm−2 (cathodic FE: 91.25% and anodic FE: 98.70%). This proceeds at a cell voltage of ca. 2.32 V, which is ca. 0.85 V lower than that of OER-assisted CO2RR system at the same current density. This work provides new insights for co-upgrading CO2 and biomass to value-added chemicals.