January 7, 2016

Partially Oxidized Atomic Cobalt Layers for Carbon Dioxide Electroreduction to Liquid Fuel

(January 7, 2016)  Prof. XIE Yi and Prof. SUN Yongfu’s group from Hefei National Laboratory for Physical Sciences at the Microscale (HFNL)  in the University of Science and Technology of China (USTC) has achieved new progress in the field of atomically-thin two-dimensionalhybrid materials. Their research group constructs a new metal atomic layer with its native oxide, with efforts to disclose the crucial role of surface metal oxide in the electrocatalytic activity of its own metal, adapted from an existing cobalt-based catalyst. This work is published on Jan 4th in Nature with the title of “Partially oxidized atomic cobalt layers for carbon dioxide electroreduction to liquid fuel”.

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 climate. However, the large barrier of CO2 activation into CO2˙ˉ or other intermediates unfortunately results in impractically high overpotentials, thus enabling it to be the most critical bottleneck in developing efficient CO2 electroreduction. Recently, electrocatalysts based on oxide-derived metal nanostructures were shown to enable CO2 reduction at low potentials. 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 defects influence CO2 reduction activity yet are difficult to control.

To tackle all these problems, they construct an ideal model of metal atomic layer with its native oxide to evaluate CO2 reduction in two well-defined catalytic sites. As a prototype, they fabricate 4-atom-thick layers of co-existing Co metal and Co oxide domains, in which the Co oxide domain is embedded in the metallic Co lattice. Base on the electrocatalytic results, they find that surface Co atoms confined in the synthetic 4-atom-thick layers of pure Co metal have higher intrinsic activity and selectivity toward formate production, at lower overpotentials, than surface Co atoms on bulk samples. Compared to the pure Co 4-atom-thick layers, the partially oxidized atomic cobalt layers exhibit further increased intrinsic activity, realizing stable current densities of ~10 mA cm-2 over 40 hours, with ~90% formate selectivity at an overpotential of only 0.24 V, which outperforms previously reported metal or metal oxide electrodes evaluated under comparable conditions. This present work demonstrates that if placed in the correct morphology and oxidation state, a material considered nearly non-catalytic for the CO2 electroreduction reaction can turn into an active catalyst. These findings point to novel 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 more fully understood.

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