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Preventing the Deactivation of Gold Cathodes During Electrocatalytic CO 2 Reduction While Avoiding Gold Dissolution
Electrocatalysis ( IF 3.1 ) Pub Date : 2019-10-26 , DOI: 10.1007/s12678-019-00564-z
Hani Taleshi Ahangari , Aaron T. Marshall

The electrochemical reduction of CO2 on gold cathodes was investigated, and the major products were found to be CO, H2 and formate, which is consistent with existing literature. The Faradaic efficiency for CO production decreased from around 60 to 10% over the course of 4 h when the electrolysis was performed at – 5 mA cm–2 in 0.2 M KHCO3 saturated with CO2. This deactivation was accompanied by an increase in the selectivity of the cathode towards H2 and formate production, which is normally attributed to the deposition of metals from trace impurities in the electrolyte or surface-bound species formed during the reaction. In this case, the deactivation was found to be due to the deposition of Cu, Zn and possibly Fe from the electrolyte, with the presence of Fe strongly enhancing H2 production, the Cu deposition increasing the formate production rate and Zn enhancing both H2 and formate production. While the accumulation of these poisons can be prevented with periodic anodic treatments (using methods previously described in the literature), these treatments lead to significant gold dissolution, with up to 450 ppb of gold found in the electrolyte after 4 h of electrolysis, and thus is unsuitable for use in long-term CO2 reduction systems. This dissolution is expected to alter the surface structure and thus selectivity of the cathode. Therefore, alternative electrochemical cleaning protocols (periodic cyclic voltammetry, open-circuit and low anodic current treatments) were investigated as methods to remove these poisons without significant gold corrosion occurring. The best approach to prevent the deactivation of gold cathodes during CO2 reduction is to cycle the potential between − 0.5 and 0.5 V vs Ag|AgCl every 15 min during long-term electrolysis. It is also shown that simply interrupting the CO2 reduction process every 15 min with 4 min at open circuit can also partially prevent the deactivation of the CO2 reduction reaction as will short anodic current pulses.

中文翻译:

在避免金溶解的同时防止电催化还原CO 2时金阴极失活

研究了金阴极上CO 2的电化学还原,发现主要产物为CO,H 2和甲酸盐,与现有文献一致。当在– 5 mA cm –2的条件下,在充满CO 2的0.2 M KHCO 3中进行电解时,在4个小时内,法拉第生产CO的效率从60%降至10%。该失活伴随着阴极对H 2的选择性增加。甲酸盐的产生,通常归因于电解液中痕量杂质或反应过程中形成的表面结合物质中金属的沉积。在这种情况下,发现失活是由于电解液中的Cu,Zn和可能的Fe沉积所致,Fe的存在极大地增强了H 2的产生,Cu的沉积提高了甲酸的产生速率,而Zn增强了H 2的生成量和甲酸生产。尽管可以通过定期阳极处理(使用先前在文献中描述的方法)来防止这些毒物的积累,但这些处理会导致金的显着溶解,电解4小时后,电解液中的金含量高达450 ppb,因此不适合长期使用2个还原系统。预期这种溶解会改变表面结构,从而改变阴极的选择性。因此,研究了替代性的电化学清洁方案(周期性循环伏安法,开路和低阳极电流处理),作为去除这些有毒物质而又不发生明显金腐蚀的方法。防止CO 2还原过程中金阴极失活的最佳方法是,在长期电解过程中,每15分钟使电势相对于Ag | AgCl的电势在-0.5至0.5 V之间。还显示出,每隔15分钟中断一次CO 2还原过程,在开路时中断4分钟,也可以部分防止CO 2失活。 还原反应,会缩短阳极电流脉冲。
更新日期:2020-01-14
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