Electrochemical Reduction of CO₂ on Ir_xRu_(1–x)O₂(110) Surfaces 

High overpotentials and low faradic efficiencies plague metal catalysts for direct conversion of CO₂ to methanol and other liquid fuels. RuO₂-based electrocatalysts have been observed to evolve methanol at low overpotentials, which has been attributed to an alternative reaction mechanism with oxygen-coordinated intermediates that can circumvent the limitations imposed by the scaling relations on metal catalysts. Here, we introduce an innovative concept of ligand effects in oxide catalysts. Both IrO₂ and RuO₂ binds OH* and other intermediates from the electrochemical reduction of CO₂ (CO2RR) strongly, but the stable and miscible system Ir_xRu_(1-x)O₂ exhibits anomalous weaker binding energy in the presence of CO* spectators, because of Ru–Ir ligand effects. The weakened adsorbate binding leads to a very low CO2RR onset potential (methanol evolution at −0.2 V RHE). An Ir atom at the bridge site with Ru neighbors binds intermediates such as OH* and OCHO* much weaker, because of synergistic ligand effects and adsorbate–adsorbate interactions. Consequently, a RuO₂ surface doped with Ir move close to the top of the predicted CO2RR volcano for oxides, which offers a significant improvement over state-of-the-art electrocatalysts for conversion of CO₂ into methanol. Analysis of electronic structure parameters with adsorbate binding energies indicates the ligand effect depletes electrons from the Ir atom and shifts the t_2g orbitals. The lack of electron donation from CO* spectators to Ir at the active site cause favorable adsorbate binding.