Ligand effects are of major interest in catalytic reactions owing to their potential critical role in determining the reaction activity and selectivity. Herein, we report ligand effects in the CO₂ electrochemical reduction reaction at the atomic level with three unique Au₂₅ nanoclusters comprising the same kernel but different protecting ligands (–XR, where X = S or Se, and R represents the carbon tail). It is observed that a change in the carbon tail shows no obvious impact on the catalytic selectivity and activity, but the anchoring atom (X = S or Se) strongly affects the electrocatalytic selectivity. Specifically, the S site acts as the active site and sustains CO selectivity, while the Se site shows a higher tendency of hydrogen evolution. Density functional theory (DFT) calculations reveal that the energy penalty associated with the *COOH formation is lower on the S site by 0.26 eV compared to that on the Se site. Additionally, the formation energy of the product (*CO) is lower on the sulfur-based Au nanocluster by 0.43 eV. We attribute these energetic differences to the higher electron density on the sulfur sites of the Au nanocluster, resulting in a modified bonding character of the reaction intermediates that reduce the energetic penalty for the *COOH and *CO formation. Overall, this work demonstrates that S/Se atoms at the metal–ligand interface can play an important role in determining the overall electrocatalytic performance of Au nanoclusters.

中文翻译：

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配体在原子精确的纳米簇催化的CO2电化学还原中的作用

由于配体作用在确定反应活性和选择性方面具有潜在的关键作用，因此它们在催化反应中引起了极大的关注。在这里，我们报告了在CO ₂电化学还原反应中，在原子级上具有三种独特的Au _25的配体效应包含相同内核但保护配体不同的纳米簇（–XR，其中X = S或Se，R代表碳尾）。观察到碳尾的变化对催化选择性和活性没有明显影响，但是锚定原子（X = S或Se）强烈影响电催化选择性。具体地，S位点充当活性位点并维持CO选择性，而Se位点显示出更高的氢释放趋势。密度泛函理论（DFT）计算表明，与* COOH形成相关的能量损失在S位上比在Se位上低0.26 eV。另外，产物（* CO）的形成能在硫基Au纳米簇上低0.43 eV。我们将这些高能差异归因于Au纳米团簇的硫位点上的更高电子密度，从而导致反应中间体的键合特性发生了改变，从而降低了* COOH和* CO形成的能量损失。总体而言，这项工作表明，金属-配体界面上的S / Se原子在决定Au纳米团簇的整体电催化性能方面可以发挥重要作用。