The Wang Lab has developed a copper nanocube catalyst by Cu2+ ion battery cycling method that efficiently converts CO2 into high value hydrocarbon products like ethylene, ethanol and n-propanol. Combining density functional theory simulation on the facet dependence of the initial Carbon-Carbon coupling steps, this work demonstrates a vivid feedback loop between theory and experiment to advance the novel catalyst discovery in renewable energy applications.
K. Jiang, R.B. Sandberg, A.J. Akey, X. Liu, D.C. Bell, J.K. Nørskov, K. Chan, H. Wang, Metal ion cycling of Cu Foil for selective C-C coupling in electrochemical CO2 reduction, Nature Catalysis, Advance Online Publication (doi: 10.1038/s41929-017-0009-x).
With the fast development of advanced technologies to efficiently harvest wind or solar energies, the cost of renewable energy in the near future is expected to decrease significantly, enabling economical conversion of carbon dioxide (CO2) and water (H2O) into fuels and chemicals. The electrochemical CO2 reduction reaction (CO2RR) is a promising energy conversion process due to its mild reaction conditions and high energy efficiencies, but is currently challenging due to the low catalytic activity and product selectivity in aqueous solutions. Catalysts with suitable electronic structures have been able to reduce CO2 in water with high Faradaic efficiencies, but most of them can only catalyze two-electron reductions to carbon monoxide or formic acid products, which have more facile kinetics. Further reductions to higher-value, energy-dense hydrocarbons and alcohols, and in particular C2+ products, is desirable for applications in energy storage, transportation, and the chemical industry, but present significantly higher overpotentials. This difficulty arises from the linear scaling among activation and binding energies of reaction intermediates; the catalytic surface needs to bind *CO intermediates strongly enough to build up a sufficient coverage for further reduction or C–C coupling, but the associated activation barriers also increase with stronger *CO binding. Developing catalytic materials with appropriate electronic properties becomes critical for tuning the interplay between these two criteria for selective C–C coupling.
To overcome these challenges, the Wang group first collaborated with Karen Chan and Jens K. Nørskov group at SUNCAT, Stanford to apply an explicit model of the electrolyte to investigate solvation and cation stabilization of initial C–C coupling intermediates, which predicts both the Cu(100) and stepped facets to be more favourable for C2+ product formation over (111).
Thereafter, Wang et al. developed a metal ion cycling method to synthesize single crystalline Cu2O nanocubes with predominantly Cu2O(100) facets. By tuning the battery cycle numbers on the Cu foil, the product distributions and reaction pathways can be effectively controlled. Under CO2RR conditions, those oxide nanocubes can be reduced to polycrystalline Cu nanocubes with preferentially exposed Cu(100) facets for C–C coupling. As a result, the 100-cycled Cu-anocube
catalyst presents a sixfold improvement in the C2+ to C1 product ratio compared with the pristine polished Cu foil, with a C2+ Faradaic efficiency of over 60% and H2 below 20%, and a corresponding C2+ partial current density of more than 40 mA cm–2 in aqueous KHCO3 electrolyte.
K. Jiang, R.B. Sandberg, A.J. Akey, X. Liu, D.C. Bell, J.K. Nørskov, K. Chan, and H. Wang, Metal ion Cycling of Cu Foil for Selective C-C coupling in Electrochemical CO2 Reduction, Nature Catalysis, doi: 10.1038/s41929-017-0009-x (2018).