National Research Council of Canada. Energy, Mining and Environment
The conversion of carbon dioxide to value-added fuel using electrical energy generated intermittently from renewable energy sources is very promising in terms of energy usage reconciliation. The process converts greenhouse carbon dioxide gas to produce diverse attractive chemicals and fuels like methanol, formate, and other hydrocarbons. In this paper, the electroreduction of CO₂ to formate in aqueous solution is performed by using novel hierarchical tin oxide microsphere (HMS-SnO₂) particles deposited over gas diffusion layer electrode (HMS-SnO₂/GDE). The experiment is carried out in a divided H-type two-compartment cell with a Nafion® membrane as the diaphragm separating the cathodic and anodic compartments. The HMS-SnO₂ catalysts are synthesized by a facile hydrothermal self-assembled process using different ratios of ethanol to distilled water in the synthetic solution. Due to the outstanding catalytic activity and selectivity toward CO₂ electroreduction, SnO₂-86/GDE exhibits a high Faradaic efficiency of 62% toward formate formation at −1.7 V vs. SHE (Standard Hydrogen Electrode). The electrode durability is also observed with a stable current density over 12 h of continuous electrolysis operation. The superior performance is credited to the morphology- and size-controlled hierarchical structure, which may provide more active sites to accelerate the slow kinetics of CO₂ reduction, leading to the improved energy efficiency. During electrolysis process, KHCO₃ electrolyte is found to have some contribution to formate formation on the micro-structured tin oxide catalysts coated GDE electrode.