Competition between CO2 Reduction and Hydrogen Evolution on a Gold Electrode under Well-Defined Mass Transport Conditions
Competition between CO2 Reduction and Hydrogen Evolution on a Gold Electrode under Well-Defined Mass Transport Conditions
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DOI：
10.1021/jacs.9b10061
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发表时间：
2020-03-04
影响因子：
15
通讯作者：
Koper, Marc T. M.
中科院分区：
文献类型：
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作者：
Goyal, Akansha;Marcandalli, Giulia;Koper, Marc T. M.
金是将 CO2 (CO2RR) 电化学还原为 CO 的最具选择性的催化剂之一。然而，在水相条件下，伴随的析氢反应 (HER) 仍然不可避免。在这项工作中，开发了旋转环盘电极（RRDE）装置来定量研究质量传递在 0.1 M 碳酸氢盐电解质中金表面上这两个反应之间的竞争中的作用。有趣的是，虽然发现 CO 形成的法拉第选择性随着传质的增强而增加（从 67% 增加到 83%），但这种效应并不是由于 CO2RR 速率的增强。值得注意的是，随着圆盘旋转速率的增加，对水减少的竞争性 HER 的抑制是 CO2RR 选择性增强的原因。这可以通过以下观察来解释：在 Au 电极上，pH 值呈碱性时，水的还原性会提高。结果，随着质量传输的增强，电极表面附近的局部碱度降低，由于水的减少而抑制了HER。我们的研究表明，通过传质条件控制局部 pH 值可以调节 HER 速率，进而调节 CO2RR 的一般操作电位窗口（-0.4 至 -1 V vs RHE）中的 CO2RR 和 HER 竞争。
Gold is one of the most selective catalysts for the electrochemical reduction of CO2 (CO2RR) to CO. However, the concomitant hydrogen evolution reaction (HER) remains unavoidable under aqueous conditions. In this work, a rotating ring disk electrode (RRDE) setup has been developed to study quantitatively the role of mass transport in the competition between these two reactions on the Au surface in 0.1 M bicarbonate electrolyte. Interestingly, while the faradaic selectivity for CO formation was found to increase with enhanced mass transport (from 67% to 83%), this effect is not due to an enhancement of the CO2RR rate. Remarkably, the inhibition of the competing HER from water reduction with increasing disk rotation rate is responsible for the enhanced CO2RR selectivity. This can be explained by the observation that, on the Au electrode, water reduction improves with more alkaline pH. As a result, the decrease in the local alkalinity near the electrode surface with enhanced mass transport suppresses HER due to the water reduction. Our study shows that controlling the local pH by mass transport conditions can tune the HER rate, in turn regulating the CO2RR and HER competition in the general operating potential window for CO2RR (-0.4 to -1 V vs RHE).