Metal Phthalocyanine-Derived Single-Atom Catalysts for Selective CO2 Electroreduction under High Current Densities.

ABSTRACT

Single-atom catalysts (SACs) with atomically dispersed metal sites in nitrogen-doped carbon matrices (M-N/C) have been identified as promising candidates for the electrocatalytic CO2 reduction reaction (CO2RR). However, recent studies aiming at economic viability have been inhibited by the low faradaic efficiency (FE) and instability under high current density. Herein, we report a series of SACs derived from cyano-substituted metal phthalocyanines (MePc-CN) in ZIFs (denoted as Me-SACs (Pc)). These phthalocyanine molecules enable the efficient construction of SACs, affording higher metal loading and less variation when compared with their counterparts from metal nitrates (denoted as Me-SACs (S)). Thus, Me-SACs (Pc) exhibit higher activities and selectivities than Me-SACs (S) in H-cell measurements. In gas-diffusion electrode (GDE) setups, the unstable Fe-SAC (Pc) shows only a 50% FE of CO (FEco) at -100 mA cm-2. In contrast, Ni-SAC (Pc) exhibits a higher FEco of >96% at current densities from -10 to -200 mA cm-2 and can stably operate for over 16 h at -200 mA cm-2. The performances of Ni-SAC (Pc) are comparable to those of precious metal catalysts and the best SACs reported so far, representing a promising candidate for practical electrolyzer devices for CO2RR.