Triple-Phase Interface Engineering over an In₂O₃ Electrode to Boost Carbon Dioxide Electroreduction

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 FE_HCOOH of 82.3% and a decreased FE_H2 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.