Department of Chemical Engineering, University of California , Berkeley, California 94720, United States.
Joint Center for Artificial Photosynthesis, Material Science Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
J Am Chem Soc. 2017 Aug 16;139(32):11277-11287. doi: 10.1021/jacs.7b06765. Epub 2017 Aug 3.
The electrochemical reduction of CO is known to be influenced by the identity of the alkali metal cation in the electrolyte; however, a satisfactory explanation for this phenomenon has not been developed. Here we present the results of experimental and theoretical studies aimed at elucidating the effects of electrolyte cation size on the intrinsic activity and selectivity of metal catalysts for the reduction of CO. Experiments were conducted under conditions where the influence of electrolyte polarization is minimal in order to show that cation size affects the intrinsic rates of formation of certain reaction products, most notably for HCOO, CH, and CHOH over Cu(100)- and Cu(111)-oriented thin films, and for CO and HCOO over polycrystalline Ag and Sn. Interpretation of the findings for CO reduction was informed by studies of the reduction of glyoxal and CO, key intermediates along the reaction pathway to final products. Density functional theory calculations show that the alkali metal cations influence the distribution of products formed as a consequence of electrostatic interactions between solvated cations present at the outer Helmholtz plane and adsorbed species having large dipole moments. The observed trends in activity with cation size are attributed to an increase in the concentration of cations at the outer Helmholtz plane with increasing cation size.
CO 的电化学还原已知受到电解质中碱金属阳离子的影响；然而，尚未对此现象提出令人满意的解释。在此，我们介绍了旨在阐明电解质阳离子大小对金属催化剂还原 CO 的内在活性和选择性影响的实验和理论研究的结果。实验在电解质极化影响最小的条件下进行，以表明阳离子大小会影响某些反应产物的内在形成速率，这在 Cu(100)-和 Cu(111)定向薄膜上对 HCOO、CH 和 CHOH 以及多晶 Ag 和 Sn 上对 CO 和 HCOO 的影响最为明显。对 CO 还原的研究结果的解释得到了对乙二醛和 CO 还原的研究的启发，乙二醛和 CO 是最终产物反应途径中的关键中间体。密度泛函理论计算表明，碱金属阳离子通过存在于外亥姆霍兹平面上的溶剂化阳离子与具有大偶极矩的吸附物种之间的静电相互作用，影响形成的产物分布。随着阳离子尺寸的增加，活性与阳离子尺寸之间的观察到的趋势归因于外亥姆霍兹平面上阳离子浓度的增加。
