Transition-Metal Porphyrin-Based MOFs In Situ-Derived Hybrid Catalysts for Electrocatalytic CO 2 Reduction.

Excellent electrocatalytic CO 2 reduction reaction activity has been demonstrated by transition metals and nitrogen-codoped carbon (M-N-C) catalysts, especially for transition-metal porphyrin (MTPP)-based catalysts. In this work, we propose to use one-step low-temperature pyrolysis of the isostructural MTPP-based metal-organic frameworks (MOFs) and electrochemical in situ reduction strategies to obtain a series of hybrid catalysts of Co nanoparticles (Co NPs) and MTPP, named Co NPs/MTPP (M = Fe, Co, and Ni). The in situ introduction of Co NPs can efficiently enhance the electrocatalytic ability of MTPP (M = Fe, Co, and Ni) to convert CO 2 to CO, particularly for FeTPP. Co NPs/FeTPP endowed a high CO faradaic efficiency (FE COmax = 95.5%) in the H cell, and the FE CO > 90.0% is in the broad potential range of -0.72 to -1.22 V RHE . In addition, the Co NPs/FeTPP achieved 145.4 mA cm -2 at a lower potential of -0.70 V RHE with an FE CO of 94.7%, and the CO partial currents increased quickly to reach 202.2 mA cm -2 at -0.80 V RHE with an FE CO of 91.6% in the flow cell. It is confirmed that Co NPs are necessary for hybrid catalysts to get superior electrocatalytic activity; Co NPs also can accelerate H 2 O dissociation and boost the proton supply capacity to hasten the proton-coupled electron-transfer process, effectively adjusting the adsorption strength of the reaction intermediates.