Electrochemical Reduction of CO<sub>2</sub> on Ir<sub><i>x</i></sub>Ru<sub>(1–<i>x</i>)</sub>O<sub>2</sub>(110) Surfaces
2017-11-01T00:00:00Z (GMT) by
High overpotentials and low faradic efficiencies plague metal catalysts for direct conversion of CO<sub>2</sub> to methanol and other liquid fuels. RuO<sub>2</sub>-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 IrO<sub>2</sub> and RuO<sub>2</sub> binds OH* and other intermediates from the electrochemical reduction of CO<sub>2</sub> (CO2RR) strongly, but the stable and miscible system Ir<sub><i>x</i></sub>Ru<sub>(1‑x)</sub>O<sub>2</sub> 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 RuO<sub>2</sub> 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 CO<sub>2</sub> 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<sub>2g</sub> orbitals. The lack of electron donation from CO* spectators to Ir at the active site cause favorable adsorbate binding.