Electroreduction of CO2 into useful fuels under mild conditions is a potentially "clean" strategy for replacing fossil feedstocks and dealing with increasing CO2 emissions and their adverse effects on climate. The critical bottleneck in developing efficient CO2 electroreduction is to activate CO2 into CO2˙ˉ or other intermediates, which requires impractically high overpotentials.
Recently, electrocatalysts based on oxide-derived metal nanostructures were shown to enable CO2 reduction at low potentials. Nevertheless, how the electrocatalytic activity of these metals is influenced by their native oxides has not been well understood, mainly because microstructural features such as interfaces and defects influence CO2 reduction activity.
To clarify the crucial role of surface metal oxides in the electrocatalytic activity of their own metals, Prof. XIE Yi and Prof. SUN Yongfu's group from the University of Science and Technology of China (USTC) fabricated 4-atom-thick layers of co-existing Co metal and Co oxide domains. They found that surface Co atoms confined in the synthetic 4-atom-thick layers of pure Co metal had 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 Co layers exhibited 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, thus outperforming previously reported metal or metal oxide electrodes evaluated under comparable conditions.
Results were published in Nature on Jan. 6, 2016.
"This is a major scientific breakthrough. Although it will take a very long time before commercial use, the current development at this stage is positive and optimistic from any point of view," noted Prof. Karthish Manthiram from Caltech.
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