pH Dependence of Cu Surface Speciation in the Electrochemical CO Reduction Reaction
pH Dependence of Cu Surface Speciation in the Electrochemical CO Reduction Reaction
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DOI：
10.1021/acscatal.0c03108
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发表时间：
2020-12-04
期刊：
影响因子：
12.9
通讯作者：
Xu, Bingjun
中科院分区：
文献类型：
--
作者：
Chang, Xiaoxia;Zhao, Yaran;Xu, Bingjun
Cu表面以其将CO2和CO电化学转化为多碳（C2+）产物的能力而闻名。虽然电解质碱度对电化学CO2和CO还原反应（CO2 RR和CORR，分别）的影响已被广泛研究的Cu表面，表面Cu形态的pH依赖性的系统研究一直缺乏。在这里，我们证明了第一次的pH值依赖性的Cu表面形态和CO吸附配置在弱到强碱性电解质使用原位表面增强拉曼光谱。含氧物质，例如，CuOx/（OH）（y）在KHCO 3近中性电解质（pH = 8.9）中不存在，并且随着电解质碱度的增加，它们的起反应电位变得更加正值。同时，吸附的CO过渡从atop键（COatop）桥键的配置（CObridge）作为电解质的pH值的增加。CO被建议吸附在顶部配置仅在铜网站没有相邻的含氧物种，而CObridge带的外观与含氧物种的存在相关。表面形态的Cu微粒（Cu MP）和氧化物衍生的Cu（OD-Cu）在所有的电解质调查是相似的，而CO吸附带显示这两个表面上的细微差异，反映在相同的配置中吸附的CO的微环境的变化。C2+产物在CORR中对Cu MP的选择性随着-0. 4V-RHE下的电解质碱度而增加，这与含氧Cu物质的存在相关。然而，单独的含氧Cu物种的存在下被证明是一个不可靠的预测的CORR性能上的铜MPs和OD-铜，这可能是由于在表面Cu网站的微环境的差异。在这项工作中报告的结果强调，假设还原电位下的表面铜形态是独立的电解质pH值必须谨慎对待。
Cu surfaces are known for their ability to electrochemically convert CO2 and CO into multicarbon (C2+) products. Although the impact of the electrolyte alkalinity on the electrochemical CO2 and CO reduction reactions (CO2RR and CORR, respectively) has been extensively investigated on Cu surfaces, systematic investigation of the pH dependence of the surface Cu speciation has been lacking. Herein, we demonstrate for the first time the pH dependence of Cu surface speciation and CO adsorption configuration in weakly to strongly alkaline electrolytes using in situ surface enhanced Raman spectroscopy. Oxygen-containing species, e.g., CuOx/(OH)(y), are absent in near-neutral electrolyte of KHCO3 (pH = 8.9), and their onset potential becomes more positive with increasing the alkalinity of electrolytes. Concurrently, adsorbed CO transitions from atop-bonded (COatop) to bridge-bonded configuration (CObridge) as the pH of the electrolyte increases. CO is proposed to adsorb in the atop configuration only on Cu sites without neighboring oxygen-containing species, while the appearance of the CObridge band correlates with the presence of the oxygen-containing species. Surface speciation on Cu microparticles (Cu MPs) and oxide-derived Cu (OD-Cu) are similar in all the electrolytes investigated, while the CO adsorption bands show subtle differences on these two surfaces, reflecting variations in the microenvironment of CO adsorbed in the same configuration. Selectivity for C2+ products in the CORR on Cu MPs increases with the electrolyte alkalinity at -0.4 V-RHE, which correlates with the presence of the oxygen-containing Cu species. However, the presence of the oxygen-containing Cu species alone is shown to be an unreliable predictor of the CORR performance on Cu MPs and OD-Cu, which could be attributed to the difference in the microenvironment of the surface Cu sites. Results reported in this work highlight that the assumption that the surface Cu speciation under reducing potentials is independent of the electrolyte pH must be treated with caution.