Phipps Christine A, Hofsommer Dillon T, Toda Megan J, Nkurunziza Francois, Shah Bhoomi, Spurgeon Joshua M, Kozlowski Pawel M, Buchanan Robert M, Grapperhaus Craig A
Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States.
Conn Center for Renewable Energy Research, University of Louisville, Louisville, Kentucky 40292, United States.
Inorg Chem. 2022 Jun 27;61(25):9792-9800. doi: 10.1021/acs.inorgchem.2c01326. Epub 2022 Jun 10.
In this study, we report a pair of electrocatalysts for the hydrogen evolution reaction (HER) based on the noninnocent ligand diacetyl-2-(4-methyl-3-thiosemicarbazone)-3-(2-pyridinehydrazone) (HDMTH, HL). The neutral complexes NiL and PdL were synthesized and characterized by spectroscopic and electrochemical methods. The complexes contain a non-coordinating, basic hydrazino nitrogen that is protonated during the HER. The p of this nitrogen was determined by spectrophotometric titration in acetonitrile to be 12.71 for NiL and 13.03 for PdL. Cyclic voltammograms of both NiL and PdL in acetonitrile exhibit diffusion-controlled, reversible ligand-centered events at -1.83 and -1.79 V (vs ferrocenium/ferrocene) for NiL and PdL, respectively. A quasi-reversible, ligand-centered event is observed at -2.43 and -2.34 V for NiL and PdL, respectively. The HER activity in acetonitrile was evaluated using a series of neutral and cationic acids for each catalyst. Kinetic isotope effect (KIE) studies suggest that the precatalytic event observed is associated with a proton-coupled electron transfer step. The highest turnover frequency values observed were 6150 s at an overpotential of 0.74 V for NiL and 8280 s at an overpotential of 0.44 V for PdL. Density functional theory (DFT) computations suggest both complexes follow a ligand-centered HER mechanism where the metals remain in the +2 oxidation state.
在本研究中，我们报道了一对基于非无辜配体二乙酰-2-(4-甲基-3-硫代半卡巴腙)-3-(2-吡啶腙)(HDMTH，HL)的析氢反应(HER)电催化剂。通过光谱和电化学方法合成并表征了中性配合物NiL和PdL。这些配合物含有一个非配位的碱性肼基氮，在HER过程中会发生质子化。通过在乙腈中的分光光度滴定法测定，该氮的pKa值对于NiL为12.71，对于PdL为13.03。NiL和PdL在乙腈中的循环伏安图分别在-1.83 V和-1.79 V(相对于二茂铁鎓/二茂铁)处显示出扩散控制的、可逆的以配体为中心的事件。对于NiL和PdL，分别在-2.43 V和-2.34 V处观察到一个准可逆的、以配体为中心的事件。使用一系列中性和阳离子酸对每种催化剂在乙腈中的HER活性进行了评估。动力学同位素效应(KIE)研究表明，观察到的预催化事件与质子耦合电子转移步骤有关。观察到的最高周转频率值，对于NiL在过电位为0.74 V时为6150 s-1，对于PdL在过电位为0.44 V时为8280 s-1。密度泛函理论(DFT)计算表明，两种配合物均遵循以配体为中心的HER机制，其中金属保持在+2氧化态。
