Selective CO2 Reduction to CO in Water using Earth-Abundant Metal and Nitrogen-Doped Carbon Electrocatalysts

作者：Xin‐Ming Hu, Halvor Høen Hval, Emil Tveden Bjerglund, Kirstine Junker Dalgaard, Monica R. Madsen, Marga‐Martina Pohl, Edmund Welter, Paolo Lamagni, Kristian Birk Buhl, Martin Bremholm, Matthias Beller, Steen Uttrup Pedersen, Troels Skrydstrup, Kim Daasbjerg · 发表于：ACS Catalysis · 年份：2018 · DOI：10.1021/acscatal.8b01022 · 被引用次数：340 · 研究领域：CO2 Reduction Techniques and Catalysts、Ammonia Synthesis and Nitrogen Reduction、Ionic liquids properties and applications

Earth-abundant transition metal (Fe, Co, or Ni) and nitrogen-doped porous carbon electrocatalysts (M-N-C, where M denotes the metal) were synthesized from cheap precursors via silica-templated pyrolysis. The effect of the material composition and structure (i.e., porosity, nitrogen doping, metal identity, and oxygen functionalization) on the activity for the electrochemical CO 2 reduction reaction (CO 2 RR) was investigated. The metal-free N-C exhibits a high selectivity but low activity for CO 2 RR. Incorporation of the Fe and Ni, but not Co, sites in the N-C material is able to significantly enhance the activity. The general selectivity order for CO 2 -to-CO conversion in water is found to be Ni > Fe ≫ Co with respect to the metal in M-N-C, while the activity follows Ni, Fe ≫ Co. Notably, the Ni-doped carbon exhibits a high selectivity with a faradaic efficiency of 93% for CO production. Tafel analysis shows a change of the rate-determining step as the metal overtakes the role of the nitrogen as the most active site. Recording the X-ray photoelectron spectra and extended X-ray absorption fine structure demonstrates that the metals are atomically dispersed in the carbon matrix, most likely coordinated to four nitrogen atoms and with carbon atoms serving as a second coordination shell. Presumably, the carbon atoms in the second coordination shell of the metal sites in M-N-C significantly affect the CO 2 RR activity because the opposite reactivity order is found for carbon sup...