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.

Facile treatment tuning the morphology of Pb with state-of-the-art selectivity in CO2 electroreduction to formate.

This study presents a facile treatment to modify the commercial irregular shaped polycrystalline Pb into well-defined octahedral Pb with unique Pb(111) facets. Efficient, selective, and stable electrochemical reduction of CO2 toward formate has been achieved on the treated Pb electrode. The faradaic efficiency of formate production from the CO2RR is 98.03%, which is the highest reported to date. The results from the combination of theoretical calculations and experimental tests demonstrate that the enhanced catalytic performance on the treated Pb electrode stems from the electrode morphology characterized by a unique Pb(111) surface with lower Gibbs free energies (ΔG) for the formation of intermediate OCHO*.

HKUST-1-derived highly ordered Cu nanosheets with enriched edge sites, stepped (211) surfaces and (200) facets for effective electrochemical CO2 reduction.

A novel electrode composed of Cu nanosheets constructed from nanoparticles was synthesized by in situ electrochemical derivation from the metal-organic framework (MOF) HKUST-1. The prepared derivative electrode (HE-Cu) exhibited higher Faradaic efficiency (FE, 56.0%) of electrochemical CO2 reduction (CO2R) compared with that of pristine Cu foil (p-Cu, 32.3%) at an overpotential of -1.03 V vs. a reversible hydrogen electrode (RHE). HE-Cu also exhibited lower onset potential of CO2R as well as inhibiting the H2 evolution reaction. Electrochemical measurements revealed that HE-Cu exhibited higher CO2 adsorption (1.58-fold) and a larger electrochemical active surface area (1.24-fold) compared with p-Cu. Physicochemical characterization and Tafel analysis showed that stepped Cu (211) surfaces, (200) facets and Cu edge atoms on HE-Cu contributed significantly to the enhanced CO2R activity and/or HCOOH and/or C2 product selectivity. The FEs of HCOOH and C2 products for HE-Cu increased 1.57-fold and 10.6-fold at an overpotential of -1.19 V vs. RHE compared with p-Cu. Although CH4 was produced on p-Cu, its formation was totally suppressed on HE-Cu due to the increase of edge sites and (200) facets. Our study demonstrates that electroreduction of MOFs is a promising method to prepare novel and stable electrochemical catalysts with unique surface structures. The fabricated derivative electrode not only promoted electrochemical CO2R activity but also exhibited high C2 product selectivity.