Nickel-Nitrogen-Doped Ordered Macro-/Mesoporous Carbon Supported Ag Nanoparticles for Efficient Electrocatalytic CO2 Reduction

Electrocatalytic CO2 reduction (ECR) into high value-added chemical products has been regarded as an effective strategy to release environmental crisis caused by high concentration of CO2 in the atmosphere, because of its mild operation conditions and the ability to use renewable energy sources as power. Metal-nitrogen-doped carbon-based nanomaterials have been demonstrated as excellent catalysts for electrochemical reduction of CO2 due to their high selectivity and low cost. However, it suffers from the problem of low Faradaic efficiency at high current density, which limits their further applications. In addition, the silver-based catalysts have good catalytic activity for the electrochemical reduction of CO2 to CO, but they can only achieve high selectivity under high overpotentials. The synergistic effect in the multi-component system provides a new idea for the design of efficient electrocatalysts for carbon dioxide reduction. Herein, we first elaborately design and prepare an ordered macro-/mesoporous nickel-nitrogen-doped carbon (Ni-N-OMMC) supported silver nanoparticles composite (Ag/Ni-N-OMMC) by the use of silica colloidal crystal as the hard template and triblock copolymer Pluronic F127 as the mesoporous structure-directing agent, and study the electrocatalytic CO2 reduction performance. Due to the confinement effect, the small silver nanoparticles are successfully loaded on the Ni-N-OMMC support by in-situ chemical reduction. Compared to Ni-N-OMMC, Ag/Ni-N-OMMC exhibits better electrocatalytic activity. The Faradaic efficiency of CO is as high as 98.7% when the potential is -0.7 V vs. reversible hydrogen electrode (RHE) in 0.1 mol.L-1 KHCO3 electrolyte. Moreover, Ag/Ni-N-OMMC has a wide operating voltage range with the Faradaic efficiency of CO over 90% at -0.7.-1.0 V, and shows a high current density of CO (33.29 mA.cm(-2)) at -1.0 V. The excellent ECR performance of Ag/Ni-N-OMMC may be attributed to the synergistic effect between Ag nanoparticles and the Ni-N-OMMC support with abundant Ni-N-x active sites, as well as the high specific surface area and efficient mass/charge transfer provided by the three-dimensional interconnected ordered macro-/mesoporous structure. This study provides an idea for future design and preparation of metal-carbon composite electrocatalysts with high activity and selectivity.

Automated summary

Electrocatalytic CO2 reduction into high value-added chemical products is considered an effective strategy for addressing the environmental crisis caused by high CO2 concentration in the atmosphere. Metal-nitrogen-doped carbon-based nanomaterials have shown promise as catalysts due to their selectivity and cost-effectiveness, although they face challenges like low Faradaic efficiency at high currents. Silver-based catalysts also exhibit good activity but struggle with achieving high selectivity without high overpotentials. The synergistic effect in multi-component systems presents a new idea for designing efficient electrocatalysts.