Using density functional theory (DFT) calculations, we investigated the electrochemical reduction of CO₂ and the competing H₂ evolution reaction on ligand-protected Au₂₅ nanoclusters (NCs) of different charge states, Au₂₅(SR)₁₈^q (q = −1, 0, +1). Our results showed that regardless of charge state, CO₂ electroreduction over Au₂₅(SR)₁₈^q NCs was not feasible because of the extreme endothermicity to stabilize the carboxyl (COOH) intermediate. When we accounted for the removal of a ligand (both –SR and –R) from Au₂₅(SR)₁₈^q under electrochemical conditions, surprisingly we found that this is a thermodynamically feasible process at the experimentally applied potentials with the generated surface sites becoming active centers for electrocatalysis. In every case, the negatively charged NCs, losing a ligand from their surface during electrochemical conditions, were found to significantly stabilize the COOH intermediate, resulting in dramatically enhanced CO₂ reduction. The generated sites for CO₂ reduction were also found to be active for H₂ evolution, which agrees with experimental observations that these two processes compete. Interestingly, we found that the removal of an –R ligand from the negatively charged NC, resulted in a catalyst that was both active and selective for CO₂ reduction. This work highlights the importance of both the overall charge state and generation of catalytically active surface sites on ligand-protected NCs, while elucidating the CO₂ electroreduction mechanisms. Overall, our work rationalizes a series of experimental observations and demonstrates pathways to convert a very stable and catalytically inactive NC to an active electrocatalyst.

中文翻译：

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阐明在配体保护的Au ₂₅纳米团簇上进行CO ₂电还原的活性位点†

使用密度泛函理论（DFT）计算，我们研究了CO的电化学还原₂和竞争ħ ₂上的配体保护的金析出反应₂₅不同的电荷状态，Au中的纳米团簇（NCS）₂₅（SR）₁₈ ^q（q = - 1、0，+ 1）。我们的结果表明，无论处于何种电荷状态，由于Au2 （SR）₁₈ ^q NCs的极高吸热性可稳定羧基（COOH）中间体，因此在Au ₂₅（SR）₁₈ ^q NCs上进行CO ₂电还原是不可行的。当我们考虑从Au ₂₅（SR）₁₈ ^q去除配体（–SR和–R）时在电化学条件下，令人惊讶地我们发现，在实验施加的电势下，这是一个热力学可行的过程，生成的表面位点成为电催化的活性中心。在每种情况下，发现在电化学条件下从其表面​​失去配体的带负电荷的NC可以显着稳定COOH中间体，从而显着提高CO _2的还原率。还发现所产生的用于CO ₂还原的位点对于H _2的释放是活跃的，这与这两个过程竞争的实验观察结果一致。有趣的是，我们发现从带负电荷的NC中除去–R配体后，得到的催化剂对CO既有活性又具有选择性₂减少。这项工作突出了总体电荷状态和在配体保护的NC上产生催化活性表面位点的重要性，同时阐明了CO _2的电还原机理。总体而言，我们的工作合理化了一系列实验观察结果，并演示了将非常稳定且无催化活性的NC转化为活性电催化剂的途径。