Department of Chemistry, University of California , Riverside, California 92521, United States.
Department of Chemistry, Yonsei University , Seoul 03722, South Korea.
J Am Chem Soc. 2017 Jul 19;139(28):9728-9736. doi: 10.1021/jacs.7b05591. Epub 2017 Jul 6.
Copper electrocatalysts can reduce CO to hydrocarbons at high overpotentials. However, a mechanistic understanding of CO reduction on nanostructured Cu catalysts has been lacking. Herein we show that the structurally precise ligand-protected Cu-hydride nanoclusters, such as CuHL (L is a dithiophosphate ligand), offer unique selectivity for electrocatalytic CO reduction at low overpotentials. Our density functional theory (DFT) calculations predict that the presence of the negatively charged hydrides in the copper cluster plays a critical role in determining the selectivity of the reduction product, yielding HCOOH over CO with a lower overpotential. The HCOOH formation proceeds via the lattice-hydride mechanism: first, surface hydrides reduce CO to HCOOH product, and then the hydride vacancies are readily regenerated by the electrochemical proton reduction. DFT calculations further predict that hydrogen evolution is less competitive than HCOOH formation at the low overpotential. Confirming the predictions, electrochemical tests of CO reduction on the CuHL cluster demonstrate that HCOOH is indeed the main product at low overpotential, while H production dominates at higher overpotential. The unique selectivity afforded by the lattice-hydride mechanism opens the door for further fundamental and applied studies of electrocatalytic CO reduction by copper-hydride nanoclusters and other metal nanoclusters that contain hydrides.
铜电催化剂可以在高过电势下将 CO 还原为碳氢化合物。然而，对于在纳米结构 Cu 催化剂上 CO 还原的机理理解一直缺乏。在此，我们表明结构精确的配体保护的 Cu-氢化物纳米团簇，例如 CuHL（L 是二硫代磷酸配体），在低过电势下为电催化 CO 还原提供了独特的选择性。我们的密度泛函理论（DFT）计算预测，铜簇中带负电荷的氢化物的存在对于确定还原产物的选择性起着关键作用，从而以较低的过电势生成 HCOOH 而不是 CO。HCOOH 的形成通过晶格氢化物机理进行：首先，表面氢化物将 CO 还原为 HCOOH 产物，然后氢化物空位通过电化学质子还原很容易再生。DFT 计算进一步预测，在低过电势下，析氢反应比 HCOOH 形成的竞争小。电化学测试证实了这一预测，即在 CuHL 团簇上进行的 CO 还原反应表明，在低过电势下，HCOOH 确实是主要产物，而在更高的过电势下，H 生产占主导地位。晶格氢化物机理提供的独特选择性为进一步研究铜-氢化物纳米团簇和其他含有氢化物的金属纳米团簇的电催化 CO 还原的基础和应用研究开辟了道路。
