Partially oxidized atomic cobalt layers for carbon dioxide electroreduction to liquid fuel

Electroreduction of carbon dioxide into useful fuels helps to reduce fossil-fuel consumption and carbon dioxide emissions, but activating carbon dioxide requires impractically high overpotentials; here a metal atomic layer combined with its native oxide that requires low overpotentials to reduce carbon dioxide is developed, adapted from an existing cobalt-based catalyst. The production of useful fuels from carbon dioxide through electroreduction would be a clean way of replacing fossil fuels and reducing carbon dioxide emissions. Shan Gao et al. have turned cobalt, a metal generally considered not active for this reaction, into a very efficient electrocatalyst by synthesizing it in the form of four-atom-thick layers. This finding, and the observation that partial oxidation of the surface boosts activity further, points to a general strategy for turning otherwise unreactive metals into efficient electroreduction catalysts. Electroreduction of CO2 into useful fuels, especially if driven by renewable energy, represents a potentially ‘clean’ strategy for replacing fossil feedstocks and dealing with increasing CO2 emissions and their adverse effects on climate1,2,3,4. The critical bottleneck lies in activating CO2 into the CO2•− radical anion or other intermediates that can be converted further, as the activation usually requires impractically high overpotentials. Recently, electrocatalysts based on oxide-derived metal nanostructures have been shown5,6,7,8 to enable CO2 reduction at low overpotentials. However, it remains unclear how the electrocatalytic activity of these metals is influenced by their native oxides, mainly because microstructural features such as interfaces and defects9 influence CO2 reduction activity yet are difficult to control. To evaluate the role of the two different catalytic sites, here we fabricate two kinds of four-atom-thick layers: pure cobalt metal, and co-existing domains of cobalt metal and cobalt oxide. Cobalt mainly produces formate (HCOO−) during CO2 electroreduction; we find that surface cobalt atoms of the atomically thin layers have higher intrinsic activity and selectivity towards formate production, at lower overpotentials, than do surface cobalt atoms on bulk samples. Partial oxidation of the atomic layers further increases their intrinsic activity, allowing us to realize stable current densities of about 10 milliamperes per square centimetre over 40 hours, with approximately 90 per cent formate selectivity at an overpotential of only 0.24 volts, which outperforms previously reported metal or metal oxide electrodes evaluated under comparable conditions1,2,6,7,10. The correct morphology and oxidation state can thus transform a material from one considered nearly non-catalytic for the CO2 electroreduction reaction into an active catalyst. These findings point to new opportunities for manipulating and improving the CO2 electroreduction properties of metal systems, especially once the influence of both the atomic-scale structure and the presence of oxide are mechanistically better understood.