Strategies toward closing the anthropogenic carbon cycle using the chemical conversion of CO₂ in off-gas streams of steel-mills or cement-plants into useful molecules have become a scientific and technological priority. Of all chemical ways to convert CO₂ into hydrocarbons, the direct electrochemical coupling of water electrolysis and CO₂ reduction appears attractive, as it is a one-pot process step, occurs at ambient temperature and pressures, involves solely water and CO₂ as reactants, and may involve renewable electricity from wind, solar or hydro power plants.

The CO₂ electroreduction to gaseous C₁ products such as CO or CH₄ is often carried out on the surface of metal catalysts such as Cu, Ag or Au. At industrially relevant current densities and electrode potentials, however, these catalysts typically suffer from low faradaic C₁ product selectivities due to the competing, very fast reduction of water, i.e. the hydrogen evolution reaction. New catalyst concepts with tunable selectivity for hydrogen evolution versus CO₂ reduction are needed(1-3).

In this contribution, we share recent experimental and computational mechanistic studies(4) on the electroreduction of CO₂, CO, HCOH on metallic multi-site versus metal/heteroatom-doped carbon single-site catalysts. We provide new insight into CO selectivity trends and put particular emphasis on the competing reaction pathways to methane and methanol. We show that carbon-based single site catalysts are an intriguing cost-effective alternative to metals.

1. H. Mistry, A. S. Varela, S. Kühl, P. Strasser, B. R. Cuenya, Nanostructured electrocatalysts with tunable activity and selectivity. Nature Reviews Materials, 16009 (2016).

2. H. Mistry et al., Highly selective plasma-activated copper catalysts for carbon dioxide reduction to ethylene. Nat Commun, (2016).

3. A. S. Varela et al., Metal-Doped Nitrogenated Carbon as an Efficient Catalyst for Direct CO2 Electroreduction to CO and Hydrocarbons. Angewandte Chemie International Edition 54, 10758-10762 (2015).

4. A. Bagger, W. Ju, A. S. Varela, P. Strasser, J. Rossmeisl, Single site porphyrine-like structures advantages over metals forselective electrochemical CO2reduction. Catal Today, http://dx.doi.org/10.1016/j.cattod.2017.1002.1028 (2017).