Robust coal matrix intensifies electron/substrate interaction of nickel-nitrogen (Ni-N) active sites for efficient CO2 electroreduction at industrial current density

Abstract

Carbon encapsulating metal composites have been widely employed in electrocatalytic reduction of CO2. Though these catalysts possess relatively high selectivity towards CO, their current densities are usually low, which hardly satisfy industrial requirements. Achieving industrial current densities requires robust catalyst supports alongside efficient electron/substrate interaction at catalytically active sites. Herein, we select anthracite coal with a naturally robust architecture as the catalyst support, whose internal dense framework favours electron transport. The controllable activation method is used to form numerous micropores at the surface of coal particles without destroying the internal structures. The spatial confinement growth effect of micropores within the coal matrix contributes to the fixation of nickel-nitrogen (Ni-N) active sites within the micropores to prevent excessive agglomeration of metallic atoms, therefore enhancing the catalyst utilization. Furthermore, confinement space provided by plentiful micropores favours the adsorption of CO2, ensuring the instantaneous supply of a sufficient concentration of the substrate molecules to adjacent active sites firmly anchored in the micropores. Accordingly, the robust coal matrix can not only promote electrons from the inside to surface catalytic centres but also capture CO2 from the outside to active sites, thus intensifying the electron/substrate interaction of Ni-N active sites. In a flow cell, the coal-matrix electrocatalyst co-doped with nickel and nitrogen exhibits an industry-level current density of 223 mA cm–2, a high faradaic efficiency of 97% for CO production and a long-term stability of continuously working for as long as 120 h. Consequently, this work advances the understanding of catalyst supports in intensifying the electron/substrate interaction of active sites and hence provides new insight into the optimization of electrocatalytic performance of earth-abundant transition metals through the incorporation into the robust coal matrix.