Highly selective electrocatalytic reduction of CO2 to HCOOH over an in situ derived hydrocerussite thin film on a Pb substrate.

A metal oxide electrode has been developed for the electrochemical CO2 reduction reaction (eCO2RR). It exhibits superior activity and product selectivity towards eCO2RR by circumventing the previously encountered problem of self-reduction with high-valence metals. Specifically, a hydrocerussite [Pb3(CO3)2(OH)2] thin film has been synthesized in situ on a Pb substrate (denoted as ER-HC) by an electroreduction method using a lead-based metal-organic framework (Pb-MOF) as a precursor. The ER-HC electrode exhibits a high selectivity of 96.8% towards HCOOH production with a partial current density of 1.9 mA cm-2 at -0.88 V vs. the reversible hydrogen electrode (RHE). A higher HCOOH partial current density of 7.3 mA cm-2 has been achieved at -0.98 V vs. RHE. Physicochemical and electrochemical characterization results demonstrate that the defective hydrocerussite surface exhibits appropriate adsorption free energy of formate (HCOO-) and a lower reaction free energy for HCOOH production from CO2, which greatly boosts the eCO2RR activity and HCOOH production selectivity. The structure and eCO2RR performance of the hydrocerussite thin film remain stable in 0.1 M KHCO3 as electrolyte, ensuring its durability. Overall, this work not only provides a metal oxide electrode (metal hydroxide, to be more precise) with excellent eCO2RR performance, but also expands the in situ electrochemical derivatization strategy for the fabrication of metal oxide electrodes.