Molecular surface functionalization of In₂O₃ to tune interfacial microenvironment for enhanced catalytic performance of CO₂ electroreduction

Indium-based materials (e.g., In2O3) are a class of promising non-noble metal-based catalysts for electroreduction of carbon dioxide (CO2). However, competitive hydrogen reduction reaction (HER) on indium-based catalysts hampers CO2 reduction reaction (CO2RR) process. We herein tune the interfacial microenvironment of In2O3 through chemical graft of alkyl phosphoric acid molecules using a facile solution-processed strategy for the first time, which is distinguished from other researches that tailor intrinsic activity of In2O3 themselves. The surface functionalization of alkyl phosphoric acids over In2O3 is demonstrated to remarkably boost CO2 conversion. For example, octadecylphosphonic acid modified In2O3 exhibits Faraday efficiency for H-2 (FE ) of as low as 6.6% andFEHCOOHof 86.5% at -0.67 V vs. RHE, which are far superior to parentIn(2)O(3)counterparts (FE of H-2 H2 24.0% and FEHCOOH of 63.1%). Moreover, the enhancing effect of alkyl phosphoric acid functionalization is found to be closely related to the length of alkyl chains. By virtue of comprehensive experimental characterizations and molecular dynamics simulations, it is revealed that the modification of alkyl phosphoric acids significantly alters the interface microenvironment of the electrocatalyst, which changes the electrocatalyst surface from hydrophilic and aerophobic to hydrophobic and aerophilic. In this case, the water molecules are pushed away and more CO2 molecules are trapped, increasing local CO2 concentration at In2O3 active sites, thus leading to the significantly enhanced CO2RR and suppressed HER. This work highlights the importance of regulating the interfacial microenvironment of inorganic catalysts by molecular surface functionalization as a means for promoting the electrochemical performance in electrosynthesis and beyond.