Electrocatalytic reduction of greenhouse gas CO2 back into storable fuels using water as medium and renewable energy-generated electricity as the power input could be a potentially clean solution to meet growing energy demands and mitigate CO2 emissions. This desired technology, however, faces great challenges in practice owing to the inherently sluggish rate of CO2 reduction reaction (CO2RR) and the lack of high-performance but cost-effective electrocatalysts. Heat-treated metal and nitrogen-doped carbon (M-N-C) materials have been emerging as promising non-precious candidates for electrochemical reduction of CO2 into fuels because of their high CO2-to-CO selectivity. In M-N-C, transition metals are known as catalytic centers to influence CO2RR activities; thus exploring champion transition metals centers in M-N-C for catalyzing CO2 reduction is imperative for further developments of advanced catalysts. Herein, we report the investigation of effects of five transition metals (Cr, Mn, Fe, Co, Ni) on CO2RR activities and mechanisms using metal-doped nitrogenated carbon nanosheets with the same metal/nitrogen doping levels as model catalysts, which were fabricated by a novel molecular-level complexing with space-confinement assistance approach. The M−N complex was identified as the determining active species in CO2RR via SCN− ion poisoning probe, and the reactivity of the transition metals in M−N follows the order of Fe ≈ Ni &gt; Co &gt; Mn &gt; Cr for the reduction of CO2 to CO. The role of Fe is to reduce overpotentials, exhibiting the lowest onset overpotential of 0.19 V to yield CO on Fe-N-C, while Ni can drastically improve CO selectivity and reaction rates, reaching the highest CO Faradaic efficiency of 96% and partial current density of −8.2 mA cm−2 at a moderate overpotential of 0.65 V. It is believed that identifying the champion transition metal centers of Fe and Ni will be of great help to guide the design of high-performance M-N-C for CO2RR by selectively doping Fe and/or Ni into various nanocarbons architectures, which will pave a green way for realizing an efficient and cost-effective CO2-to-fuels process.

Identification of champion transition metals centers in metal and nitrogen-doped carbon catalysts for electrocatalytic reduction of carbon dioxide into fuels

2019 Spring National Meeting

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