Kumar Corrine A, Saha Arjun, Raghavachari Krishnan
Department of Chemistry, Indiana University , Bloomington, Indiana 47405, United States.
J Phys Chem A. 2017 Mar 2;121(8):1760-1767. doi: 10.1021/acs.jpca.6b11879. Epub 2017 Feb 17.
Transition metal sulfides (TMS) are being investigated with increased frequency because of their ability to efficiently catalyze the hydrogen evolution reaction. We have studied the trimetallic TMS cluster ions, MoS, WS, and WS, and probed their efficiency for bond activation and hydrogen evolution from water. These clusters have geometries that are related to the edge sites on bulk MoS surfaces that are known to play a role in hydrogen evolution. Using density functional theory, the electronic structures of these clusters and their chemical reactivity with water have been investigated. The reaction mechanism involves the initial formation of hydroxyl and thiol groups, hydrogen migration to form an intermediate with a metal hydride bond, and finally, combination of a hydride and a proton to eliminate H. Using this mechanism, free energy profiles of the reactions of the three metal clusters with water have been constructed. Unlike previous reactivity studies of other related cluster systems, there is no overall energy barrier in the reactions involving the MS systems. The energy required for the rate-determining step of the reaction (the initial addition of the cluster by water) is lower than the separated reactants (-0.8 kcal/mol for Mo and -5.1 kcal/mol for W). They confirm the MS cluster's ability to efficiently activate the chemical bonds in water to release H Though the WS cluster is not as efficient at bond activation, it provides insights into the factors that contribute to the success of the MS anionic systems in hydrogen evolution.
过渡金属硫化物（TMS）因其能够有效催化析氢反应而受到越来越频繁的研究。我们研究了三金属TMS簇离子MoS、WS和WS，并探究了它们对水的键活化和析氢效率。这些簇的几何结构与块状MoS表面的边缘位点相关，已知这些边缘位点在析氢过程中起作用。利用密度泛函理论，研究了这些簇的电子结构及其与水的化学反应性。反应机理包括羟基和硫醇基的初始形成、氢迁移形成具有金属氢键的中间体，最后，氢化物和质子结合以消除H。利用该机理，构建了三种金属簇与水反应的自由能剖面图。与先前对其他相关簇系统的反应性研究不同，涉及MS系统的反应中没有整体能垒。反应速率决定步骤（水对簇的初始加成）所需的能量低于分离的反应物（Mo为-0.8千卡/摩尔，W为-5.1千卡/摩尔）。它们证实了MS簇有效活化水中化学键以释放H的能力。虽然WS簇在键活化方面效率不高，但它提供了对有助于MS阴离子系统析氢成功的因素的见解。
