Thermal Transformation of Molecular Ni 2+ –N 4 Sites for Enhanced CO 2 Electroreduction Activity

Atomically dispersed nickel sites complexed on nitrogen-doped carbon (Ni–N/C) have demonstrated considerable activity for the selective electrochemical carbon dioxide reduction reaction (CO 2 RR) 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 CO 2 RR activity. H-NiPc/CNT exhibits a ∼4.7-fold higher turnover frequency for CO 2 RR 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 Ni 2+ –N 4 sites of NiPc into Ni…