Two-dimensional Cu-based Metal−Organic Frameworks as electrochemical catalysts for CO2 reduction

Abstract

IIn the past decades, the rapid development of industry and economy leads to heavy dependence on fossil fuels which causes increasing concentration of CO2 in atmosphere. Now, excessive CO2 emission has accelerated global warming and caused a series of irreversible environmental problems. To address this problem, electrochemical conversion of CO2 is considered one of the most promising strategies to due to its mild operating conditions, utilization of renewable sources of energy and controllability of the process. However, CO2 reduction faces many difficulties which requires active catalysts to achieve effective conversion. Among all the catalysts, Copper (Cu)-based Metal-Organic Frameworks (MOFs) become veryattracting candidates due to their high porosity, tunable structure and special properties to convert CO2 into various hydrocarbons. In particular, two-dimension (2D) Cu-MOFs can further improve the electrical conductivity and catalytic activity. In this study, three types of Cu-based MOFs are studied as catalysts for CO2 reduction reaction (CO2RR). Among them, Cu-BTC is a conventional 3D MOF, Cu-HAB and Cu-HHTP belong to 2D MOFs. In particular, Cu-HAB has not been used as catalyst for CO2 reduction before. To investigate their catalytic performance for CO2 reduction, the surface morphologies and bond structures were first characterized by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Fourier-transform infrared spectroscopy (FTIR). Then Linear sweep voltammetry (LSV), Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) and Chronoamperometry (CA) were used to examine the electrochemical performance and stability of them. In the last, the product selectivity of Cu-HAB and Cu-HHTP wastested using Gas Chromography (GC) and Nuclear Magnetic Resonance (NMR). From the results, 2D MOFs show higher catalytic activity, capacitance and conductivity which suggest 2D structure is beneficial for catalytic process. Especially Cu-HAB shows the best conductivity and catalytic activity due to presence of Cu-N4 coordination in the MOF structure as well as smaller particles. But from the point of view of product selectivity, Cu-HHTP performs better than Cu-HAB which may indicate Cu-O4 sites can better engage with CO2 molecule and transfer it to other products.