Effects of Ligand Modification and Protonation on Metal Oxime Hydrogen Evolution Electrocatalysts
详细信息 查看全文
- 作者：Brian H. Solis ; Yinxi Yu ; Sharon Hammes-Schiffer
- 刊名：Inorganic Chemistry
- 出版年：2013
- 出版时间：June 17, 2013
- 年：2013
- 卷：52
- 期：12
- 页码：6994-6999
- 全文大小：278K
- 年卷期：v.52,no.12(June 17, 2013)
- ISSN：1520-510X
文摘
The design of hydrogen-evolving electrocatalysts that operate at modest overpotentials is important for solar energy devices. The MII/I reduction potential for metal diimine-dioxime and diglyoxime electrocatalysts is often related to the overpotential required for hydrogen evolution. Herein the impact of ligand modification and protonation on the MII/I reduction potentials for cobalt, nickel, and iron diimine-dioxime and diglyoxime complexes is investigated with computational methods. The calculations are consistent with experimental data available for some of these complexes and additionally provide predictions for complexes that have not yet been synthesized. The calculated pKa鈥檚 imply that ligand protonation is likely to occur at the O鈥揌鈥揙 bridge but not at other ligand sites for these complexes. Moreover, the calculations imply that a ligand-protonated CoIII-hydride intermediate is formed along the H2 production pathway for catalysts containing an O鈥揌鈥揙 bridge in the presence of sufficiently strong acid. The calculated MII/I reduction potentials indicate that the anodic shift due to protonation of the O鈥揌鈥揙 bridge is greater than that due to replacing the O鈥揌鈥揙 bridge with an O鈥揃F2鈥揙 bridge for cobalt and nickel but not for iron complexes. Experiments suggest degradation for complexes with two O鈥揌鈥揙 bridges and alternative mechanisms for certain iron complexes with two O鈥揃F2鈥揙 bridges. Asymmetric cobalt, nickel, and strongly electron withdrawing substituted iron diimine-dioxime and diglyoxime complexes containing a single O鈥揌鈥揙 bridge are proposed to be effective hydrogen evolution electrocatalysts with relatively low overpotentials in acetonitrile and water. These insights are important for the design of efficient aqueous-based hydrogen-evolving catalysts.