(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.