In Situ Generated CO Enables High-Current CO2 Reduction to Methanol in a Molecular Catalyst Layer.

Molecular catalysts such as cobalt phthalocyanine (CoPc) exhibit remarkable electrochemical activity in methanol production from CO2 or CO, but fast conversion with a high current density is still yet to be realized. While adopting flow cells with gas diffusion electrodes is a common approach to enhanced reaction rates, the current scientific and engineering knowledge primarily centers on metal particle-based catalysts like Cu. This focus overlooks the emerging heterogenized molecular catalysts with distinct physical and chemical properties. In this work, we observe that the partial current density of CO reduction to methanol catalyzed by tetraamine-substituted CoPc (CoPc-NH2) supported on carbon nanotubes (CNTs) remains below 30 mA cm-2, even with systematic optimization of structural and operational parameters of the flow cell. A comparative analysis with a Cu metal catalyst reveals that the porous and electrolyte-philic nature of CoPc-NH2/CNT leaves a large fraction of active sites deprived of CO under reaction conditions. To address this microenvironmental challenge, we directly use CO2 as the reactant, leveraging its faster diffusion rate in water compared to CO. Effective CO2 reduction generates CO in situ to feed the catalytic sites, achieving an unprecedently high partial current density for methanol of 129 mA cm-2. This research underscores the necessity for new insights and approaches in the development of molecular catalyst-based electrodes.

CO2-Promoted Electrocatalytic Reduction of Chlorinated Hydrocarbons.

Electrochemical reactions and their catalysis are important for energy and environmental applications, such as carbon neutralization and water purification. However, the synergy in electrocatalysis between CO2 utilization and wastewater treatment has not been explored. In this study, we find that the electrochemical reduction of chlorinated organic compounds such as 1,2-dichloroethane, trichloroethylene, and tetrachloroethylene into ethylene in aqueous media, which is a category of challenging reactions due to the competition of H2 evolution, can be substantially enhanced by simultaneously carrying out the reduction of CO2 on an easily prepared and cost-effective Cu metal catalyst. In the case of 1,2-dichloroethane dechlorination, a 6-fold improvement in Faradaic efficiency and a 19-fold increase in partial current density are demonstrated. Through electrochemical kinetic studies, in situ Raman spectroscopy, and computational simulations, we further find that CO2 reduction reduces hydrogen coverage on the Cu catalyst, which not only exposes more active sites for the dechlorination reaction but also enhances the effective reductive potential on the catalyst surface and reduces the kinetic barrier of the rate-determining step.