Electrocatalytic reduction of CO2 to CO with 100% faradaic efficiency by using pyrolyzed zeolitic imidazolate frameworks supported on carbon nanotube networks

Abstract

Electrochemical reduction of CO₂ has received much attention because of its potential in converting atmospheric CO₂ into commodity products. One of the key challenges in electrochemical CO₂ reduction is the competing hydrogen evolution reaction (HER) at reduction electrode potentials. In this work, we used a hybrid material composed of pyrolyzed zeolitic imidazolate frameworks (ZIFs) and multi-walled carbon nanotubes (MWCNTs) to selectively catalyze electrochemical reduction of CO₂ to CO in aqueous solution with close to 100% faradaic efficiency and a current density up to 7.7 mA cm⁻² at an overpotential of 740 mV. The MWCNT support is crucial to achieving superior selectivity, thanks to enhanced electron transport on the MWCNT network and expedited CO₂ transport in the mesoporous structure constructed by the MWCNTs. Moreover, doping Fe into the hybrid further reduces the overpotential of CO₂ reduction to 440 mV with a current density of 2 mA cm⁻² and a CO faradaic efficiency of 97%. This work highlights the importance of optimizing electron and mass transport in turning moderate catalysts into superior ones with high activity and selectivity for CO₂ reduction.