Cyclic two-step electrolysis for stable electrochemical conversion of carbon dioxide to formate.

Pd metal and Pd-based alloys are ideal catalysts that allow for the electrochemical conversion of CO₂ to HCOO⁻ at almost zero-overpotential with high selectivity, but catalyst degradation caused by concurrent CO poisoning limits their practical implementation. Here, we demonstrate that cyclic two-step electrolysis, by applying the reduction and oxidation potentials alternately, achieves 100% current density stability and 97.8% selectivity toward HCOO⁻ production for at least 45 h. The key idea for achieving the reliability is based on the selective removal of CO by controlling the parameters during the oxidation step, which utilizes the different reversibility of HCOO⁻ and CO production reactions. Furthermore, it is found that potentiostatic electrolysis causes CO adsorption and subsequent dehydridation, which in turn lowers HCOO⁻ selectivity. Our work provides a system-level strategy for solving the poisoning issue that is inevitable in many electrocatalytic reactions. Reduction of carbon dioxide is promising for the production of value-added chemicals, but electrocatalysts are hindered by carbon monoxide poisoning. Here, the authors alternate reduction and oxidation potentials to achieve stable and selective long-term electrocatalytic reduction of carbon dioxide to formate. [ABSTRACT FROM AUTHOR]