The electrocatalytic reduction of CO2 is deemed to be a promising method to ease environmental and energy issues. However, achieving high efficiency and selectivity of CO2 electroreduction remains a bottleneck due to huge limitation of CO2 mass transfer and competition of hydrogen evolution reaction (HER) in aqueous solution. In this work, we propose to utilize triple-phase interface engineering over an In2O3 electrode to enhance its CO2 reduction reaction (CO2RR) performance. Notably, distinguishing from other research studies (doping, defect introduction, and heterojunction construction) that regulate the nature of In2O3-based catalysts themselves, we herein tune interfacial wettability of In2O3 using facile fluoropolymer coating for the first time. In contrast to the hydrophilic In2O3 electrode [Faraday efficiency (FE)HCOOH ∼ 62.7% and FEH2 ∼ 24.1% at -0.67 V versus RHE], the hydrophobic fluoropolymer (taking polyvinylidene fluoride as an example)-coated In2O3 electrode delivers a significantly enhanced FEHCOOH of 82.3% and a decreased FEH2 of 5.7% at the same potential. Upon combining contact angle measurements, density functional theory calculation, and ab initio molecular dynamics simulation, the enhanced CO2RR performance is revealed to be attributed to the rich triple-phase interfaces formed after fluoropolymer coating as an "aerophilic sponge", which increases the local concentration of CO2 near In2O3 active sites to improve CO2 reduction and meanwhile reduces the accessible water molecules to suppress competitive HER. This work presents a feasible approach for the enhanced selectivity of HCOOH yield over In2O3 by triple-phase interface engineering, which also provides a convenient and effective method for developing other materials used in gas-consumption reactions.
Keywords: CO2 electroreduction; polymer coating; theory calculation insight; triple-phase interface; water and CO2 diffusion.