A team from Tohoku University, Tokyo University of Science and Vanderbilt University have developed a novel pathbreaking copper nanocluster. This work has tremendous implications for improving the state of the art in electrochemical carbon dioxide (CO₂) reduction. This breakthrough development highlights the potential for more efficient and selective conversion of CO₂ into useful chemicals, particularly formic acid and carbon monoxide.
The newly developed copper nanocluster, Cu₂₃, possesses high stability and superior selectivity toward electrochemical reactions of both acetic acid and acetic salt. This next-generation semiconductor is built with an atomically precise structure. It represents a significant improvement from other copper-based catalysts, which are prone to instability. The results, which highlight the nanocluster’s promise in advancing sustainable chemistry, were detailed in a recent study.
Key Achievements of the Copper Nanocluster
Cu₂₃ nanocluster endows outstanding performance weights in electrochemical CO₂ reduction. At an applied potential of -1.2 V vs. RHE, it exhibits a Faradaic efficiency of ~26%. As a result of this efficiency, the overall product is formic acid, which is a valuable chemical feedstock. Moreover, the nanocluster exhibits a Faradaic efficiency of ∼2.6% for carbon monoxide at similar conditions.
Such efficiencies are pretty darn important as they get into the commercial viability of these CO₂ conversion techs. Given the potential value of producing formic acid at high enough rates, there is the potential to reap very large economic advantages. Just as importantly, it’s central to cutting greenhouse gas emissions. The atomically precise nature of the Cu₂₃ cluster plays a key role in stabilizing key reaction intermediates to enhance overall selectivity. The *HCOO intermediate is key for producing formic acid.
Structural Advantages and Active Sites
A proposed geometric structural formula for closed Cu₂₃ nanocluster is shown as [Cu₂₃H₄(SC₇H₇)₁₈(PPh₃)₆], involving the usage of p-toluenethiolate (SC₇H₇) and triphenylphosphine (PPh₃) stabilizing ligands. That unusual architecture contributes substantially to stability. It increases the number of active sites on its surface, enabling as much reactants to easily access the active site during electrochemical reactions.
These dynamic sites are important for the structural stability of the Cu₂₃ nanocluster. Furthermore, they enable it to optimize the stabilization of the *HCOO intermediate. It aids product selectivity and stabilizes key reaction intermediates. This has the effect of lowering the limiting potential needed for the reaction to happen, making the overall process far less energetically intensive than other catalysts.
Implications for Future Research
The ramifications of this finding reach far beyond current uses. Professor Yuichi Negishi of Tohoku University commented on the significance of the research:
“This study demonstrates a new paradigm in the design of metal nanoclusters.”
This careful weighing of the prospects versus the challenges bears out the larger promise of creating new, functional nanomaterials with Earth-abundant metals such as copper. These fundamental findings reveal that well-defined Cu architectures are outstanding catalysts. Their natural volatility has limited their real world application. Although the additional introduction of the Cu₂₃ cluster brings a high stability of the catalytic material, the excellent catalytic activity should be kept.
While the Cu(I) state presents stability that is advantageous, the lack of required versatility in catalytic processes makes it less favorable. This newly created copper nanocluster represents a watershed development. It not only addresses current shortcomings but enhances the effectiveness of CO₂ removal and other reduction technologies.