Metal–organic framework derived single-atom catalysts for electrochemical CO(2) reduction

With maximum atomic utilization, transition metal single atom catalysts (SACs) show great potential in electrochemical reduction of CO(2) to CO. Herein, by a facile pyrolysis of zeolitic imidazolate frameworks (ZIFs) assembled with tiny amounts of metal ions, a series of metal–nitrogen–carbon (M–N–C) based SACs (M = Fe, Ni, Mn, Co and Cu), with metal single atoms decorated on a nitrogen-doped carbon support, have been precisely constructed. X-ray photoelectron spectroscopy (XPS) for M–N–C showed that the N 1s spectrum was deconvoluted into five peaks for pyridinic (∼398.3 eV), M–N coordination (∼399.6 eV), pyrrolic (∼400.4 eV), quaternary (∼401.2 eV) and oxidized (∼402.9 eV) N species, demonstrating the existence of M–N bonding. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) indicates homogeneous distribution of metal species throughout the N-doped carbon matrix. Among the catalysts examined, the Fe–N–C catalyst exhibits the best catalytic performance in electrocatalytic CO(2) reduction reaction (CO(2)RR) with nearly 100% faradaic efficiency for CO (FE(CO)) at −0.9 V vs. the reversible hydrogen electrode (RHE). Ni–N–C is the second most active catalyst towards CO(2)RR performance, then followed by Mn–N–C, Co–N–C and Cu–N–C. Considering the optimum activity of Fe–N–C catalyst for the CO(2)RR, we then further investigate the effect of pyrolysis temperature on CO(2)RR of the Fe–N–C catalyst. We find the Fe–N–C catalyst pyrolyzed at 1000 °C exhibits the best catalytic activity in CO(2)RR with excellent CO selectivity.