Joint Center for Artificial Photosynthesis, Material Science Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
Department of Chemical Engineering, University of Illinois at Chicago , Chicago, Illinois 60607, United States.
J Am Chem Soc. 2016 Oct 5;138(39):13006-13012. doi: 10.1021/jacs.6b07612. Epub 2016 Sep 26.
Electrolyte cation size is known to influence the electrochemical reduction of CO over metals; however, a satisfactory explanation for this phenomenon has not been developed. We report here that these effects can be attributed to a previously unrecognized consequence of cation hydrolysis occurring in the vicinity of the cathode. With increasing cation size, the pK for cation hydrolysis decreases and is sufficiently low for hydrated K, Rb, and Cs to serve as buffering agents. Buffering lowers the pH near the cathode, leading to an increase in the local concentration of dissolved CO. The consequences of these changes are an increase in cathode activity, a decrease in Faradaic efficiencies for H and CH, and an increase in Faradaic efficiencies for CO, CH, and CHOH, in full agreement with experimental observations for CO reduction over Ag and Cu.
电解质阳离子的大小会影响金属对 CO 的电化学还原；然而，对于这一现象还没有令人满意的解释。我们在这里报告，这些影响可以归因于在阴极附近发生的阳离子水解的一个以前未被认识到的后果。随着阳离子尺寸的增加，阳离子水解的 pK 值降低，并且对于水合的 K、Rb 和 Cs 来说，其足够低，可以作为缓冲剂。缓冲作用降低了阴极附近的 pH 值，导致溶解的 CO 的局部浓度增加。这些变化的结果是阴极活性的增加，H 和 CH 的法拉第效率降低，以及 CO、CH 和 CHOH 的法拉第效率增加，这与在 Ag 和 Cu 上进行 CO 还原的实验观察完全一致。
