Sa, Young Jin Jung, Hyejin Shin, Dongyup Jeong, Hu Young Ringe, Stefan Kim, Hyungjun Hwang, Yun Jeong Joo, Sang Hoon 2024-01-19T16:31:36Z 2024-01-19T16:31:36Z 2021-09-02 2020-10-02 2155-5435 https://pubs.kist.re.kr/handle/201004/118007 Atomically dispersed nickel sites complexed on nitrogen-doped carbon (Ni-N/C) have demonstrated considerable activity for the selective electrochemical carbon dioxide reduction reaction (CO2RR) to CO. However, the high-temperature treatment typically involved during the activation of Ni-N/C catalysts makes the origin of the high activity elusive. In this work, Ni(II) phthalocyanine molecules grafted on carbon nanotube (NiPc/CNT) and heat-treated NiPc/CNT (H-NiPc/CNT) are exploited as model catalysts to investigate the impact of thermal activation on the structure of active sites and CO2RR activity. H-NiPc/CNT exhibits a similar to 4.7-fold higher turnover frequency for CO2RR to CO in comparison to NiPc/CNT. Extended X-ray absorption fine structure analysis and density functional theory (DFT) calculations reveal that the heat treatment transforms the molecular Ni2+-N-4 sites of NiPc into Ni+-N3V (V: vacancy) and Ni+-N-3 sites incorporated in the graphene lattice that concomitantly involves breakage of Ni-N bonding, shrinkage in the Ni-N-C local structure, and decrease in the oxidation state of the Ni center from +2 to +1. DFT calculations combined with microkinetic modeling suggest that the Ni-N3V site appears to be responsible for the high CO2RR activity because of its lower barrier for the formation of * COOH intermediate and optimum *CO binding energy. In situ/operando X-ray absorption spectroscopy analyses further corroborate the importance of reduced Ni+ species in boosting the CO2RR activity. English AMER CHEMICAL SOC EFFICIENT ELECTROCATALYTIC ACTIVITY ELECTROCHEMICAL REDUCTION CARBON-DIOXIDE ORGANIC FRAMEWORKS OXYGEN REDUCTION SINGLE ATOMS NICKEL SITES METAL SELECTIVITY CATALYSTS Thermal Transformation of Molecular Ni2+-N-4 Sites for Enhanced CO2 Electroreduction Activity Article 10.1021/acscatal.0c02325 1 ACS CATALYSIS, v.10, no.19, pp.10920 - 10931 ACS CATALYSIS 10 19 10920 10931 scie scopus 000577156300010 2-s2.0-85094209051 Chemistry, Physical Chemistry Article EFFICIENT ELECTROCATALYTIC ACTIVITY ELECTROCHEMICAL REDUCTION CARBON-DIOXIDE ORGANIC FRAMEWORKS OXYGEN REDUCTION SINGLE ATOMS NICKEL SITES METAL SELECTIVITY CATALYSTS Ni-N/C catalyst electrochemical CO2 reduction heat treatment local structure oxidation state