No abstract

Electrochemical CO2 reduction reaction (CO2RR) is an attractive solution to close the anthropogenic carbon cycle and store intermittent renewable energy in value-added chemicals and fuels. While Fe nanoparticles are typically employed as catalysts for hydrogen evolution reaction (HER, a competing reaction against CO2RR), herein, efficient CO2 electroreduction is achieved through tuning their chemical microenvironment. Porous carbon layers were deposited on these Fe nanoparticles, which creates a hydrophobic environment to enrich local CO2 concentration and suppress water penetration and thus HER in the micropores. This strategy successfully turns Fe nanoparticles into an excellent CO2RR catalyst with over 90% CO Faradaic efficiency. Due to the unique local chemical environment created above, high CO selectivity could be maintained even in acidic electrolytes, which provides a promising approach to address the notorious issue of carbonate precipitation in widely used alkaline solutions for CO2 electrolyzers.

Excessive carbon dioxide emissions cause severe global warming issues. One efficient way to deal with the problem is to convert CO 2 into valuable fuels and chemicals. The electrocatalytic carbon dioxide reduction reaction (CO 2 RR) has an excellent potential to reduce carbon emissions. Over the past few decades, research in this field has focused on creating highperformance catalysts. However, the overall efficiency of the CO 2 RR process is limited at the device level, such as slow CO 2 mass transportation causing insufficient current density output, which is an urgent issue to be overcome in the design of advanced CO 2 RR electrolyzers. Recently, gas diffusion electrodes have been intensively investigated to raise the CO 2 RR performance into commercially relevant current densities by boosting the CO 2 mass transport rate. This review focuses on recent research progress on electrode engineering for increasing the CO 2 RR performance, along with electrode-stabilizing strategies for long-term CO 2 electrolysis. Future directions are proposed to accelerate the development of advanced electrodes for industrial CO 2 electrolyzers.

Single-atom catalysts within M-N-C structures are efficient for electrochemical CO 2 reduction. However, most of them are powdered and require a coating process to load on the electrode. Herein, we developed a facile approach to the synthesis of largescale self-supported porous carbon nanofiber electrodes directly decorated with atomically dispersed nickel active sites using facile electrospinning, where poly(methyl methacrylate) was employed to tune well the distributions of pores located in carbon nanofibers. The above self-supported carbon nanofibers were applied as a gas diffusion electrode to achieve 94.3% CO Faraday efficiency and 170 mA cm −2 current density, which can be attributed to the effects of rich mesoporous structures favorable for adsorption and mass transfer of CO 2 and single nickel catalysts effectively converting CO 2 to CO. This work provides an efficient strategy to fabricate self-supported electrodes and may accelerate the progress toward industrial applications of single-atom catalysts in the field of CO 2 electroreduction.

Electrochemical carbon dioxide reduction reaction (CO2RR) to multicarbon (C2+) compounds holds great potential for achieving carbon neutrality and storing intermittent renewable energy. The formation of carbon–carbon (C–C) bonds, affected by the concentration of *CO intermediates on the surface of catalysts, is critical to facilitate the production of C2 species. Here, a novel method to prepare uniform hollow oxide-derived copper crystals is reported, reducing CO2 to C2 products (ethylene and ethanol) with an outstanding Faradaic efficiency of 71.1% in 0.1 M KHCO3. The degree of hollowness shows a positive tendency to C2 selectivity but negative to H2 and C1 selectivity. In situ surface-enhanced infrared absorption spectroscopy indicates that hollow structures enhance localized *CO concentration, boosting C–C coupling for producing C2 products. This provides a feasible strategy to enrich important intermediates to deeper reduction products through catalyst structure engineering.