The direct electrochemical reduction of CO₂ to fuels and chemicals using renewable electricity has attracted much attention in part due to the fundamental surface catalytic challenges related to activity and selectivity, in part owing to its potential practical importance in CO₂ valorization for energy and chemicals application.¹ In particular, the selective 2-electron reduction to CO has captivated chemists’ and engineers’ minds for the design of technological CO₂-consuming cathodes (CCCs) for use as counter electrodes in the polymer-chloralkaline industries, where fossil-based CO currently still serve as feedstock for production of e.g. polycarbonate and polyurethanes. Work on solid catalysts for the selective electrochemical reduction of CO₂ to CO has been limited to the traditional noble metal catalysts such as Ag and Au.² Here, we present new advances in our understanding of the CO₂ reduction process on N-coordinated, non-noble metal-doped nano-porous carbons (M-N-C, M=Mn, Fe, Co, Ni, Cu). These materials are single site catalysts comprising active M-N_x moieties. We investigate the trends in their intrinsic electrochemical reactivity, CO turnover frequencies, and CO efficiencies and show that Fe-N-C and Ni-N-C catalysts outperform Au or Ag. We model the active site by Density Functional Theory (DFT) and arrive at a consistent atomic-scale understanding of their potential-dependent CO and hydrocarbon selectivity. Linking DFT predictions directly with experiments we explain why Fe-N-C and Ni-N-C represent the most cost-effective and energy-efficient carbon-based catalysts for future CO generation inside CCCs.

References:

1 Huei-Ru “Molly” Jhong, S. M., Paul JA Kenis. Electrochemical conversion of CO2 to useful chemicals: current status, remaining challenges, and future opportunities. Current Opinion in Chemical Engineering 2, 191-199 (2013).

2 AS Varela, N. S., J Steinberg, W Ju, HS Oh, P Strasser. Metal-Doped Nitrogenated Carbon as an Efficient Catalyst for Direct CO2 Electroreduction to CO and Hydrocarbons. Angew. Chem. Int. Ed. 54, 10758–10762 (2015).