Abstract
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.
Highlights
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
In summary, we have demonstrated that the inherent poisoning issue of Pd-based catalysts in electrochemical CO2 reduction reactions can be resolved via cyclic two-step electrolysis, an electrochemical method to apply the reduction and oxidation steps alternately
Though HCOO− production and CO adsorption simultaneously occurred in the reduction step, the CO molecules were selectively oxidized in the anodic step
Summary
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. We discuss the degradation mechanism using electrochemical surface analysis, and based on the understanding, we propose cyclic two-step electrolysis, applying reduction and oxidation potentials alternately, as a strategy for securing both stability and selectivity for HCOO− production. Two-step electrolysis can decouple the HCOO− formation from CO adsorption by selectively oxidizing CO.
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