Ezhov Roman, Bury Gabriel, Maximova Olga, Grant Elliot Daniel, Kondo Mio, Masaoka Shigeyuki, Pushkar Yulia
Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907 USA.
Division of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
J Catal. 2024 Jan;429. doi: 10.1016/j.jcat.2023.115230. Epub 2023 Nov 29.
Photoelectrochemical water splitting can produce green hydrogen for industrial use and CO-neutral transportation, ensuring the transition from fossil fuels to green, renewable energy sources. The iron-based electrocatalyst [FeFe(μ-3-O)(μ-)] (H = 3,5-bis(2-pyridyl)pyrazole) , discovered in 2016, is one of the fastest molecular water oxidation catalysts (WOC) based on earth-abundant elements. However, its water oxidation reaction mechanism has not been yet fully elucidated. Here, we present X-ray spectroscopy and electron paramagnetic resonance (EPR) analysis of electrochemical water oxidation reaction (WOR) promoted by in water-acetonitrile solution. We observed transient reactive intermediates during the electrochemical WOR, consistent with a coordination sphere expansion prior to the onset of catalytic current. At a pre-catalytic (+1.1 V . Ag/AgCl) potential, the distinct g2.0 EPR signal assigned to Fe/Fe interaction was observed. Prolonged bulk electrolysis at catalytic (~+1.6 V . Ag/AgCl) potential leads to the further oxidation of Fe centers in At the steady state achieved with such electrolysis, the formation of hypervalent Fe=O and Fe=O catalytic intermediates was inferred with XANES and EXAFS fitting, detecting a short Fe=O bond at ~1.6 Å. was embedded into MIL-126 MOF with the formation of -MIL-126 composite. The latter was tested in photoelectrochemical WOR and demonstrated an improvement of electrocatalytic current upon visible light irradiation in acidic (pH=2) water solution. The presented spectroscopic analysis gives further insight into the catalytic pathways of multinuclear systems and should help the subsequent development of more energy- and cost-effective catalysts of water splitting based on earth-abundant metals. Photoelectrocatalytic activity of -MIL-126 confirms the possibility of creating an assembly of inside a solid support and boosting it with solar irradiation towards industrial applications of the catalyst.
光电化学水分解能够产生用于工业用途和碳中和运输的绿色氢气，确保从化石燃料向绿色可再生能源的过渡。2016年发现的铁基电催化剂[FeFe(μ-3-O)(μ-)] (H = 3,5-双(2-吡啶基)吡唑)是基于地球上储量丰富元素的最快分子水氧化催化剂(WOC)之一。然而，其水氧化反应机理尚未完全阐明。在此，我们展示了在水-乙腈溶液中由[FeFe(μ-3-O)(μ-)] (H = 3,5-双(2-吡啶基)吡唑)促进的电化学水氧化反应(WOR)的X射线光谱和电子顺磁共振(EPR)分析。我们在电化学WOR过程中观察到瞬态反应中间体，这与催化电流开始之前的配位球扩张一致。在预催化（~ +1.1 V vs. Ag/AgCl）电位下，观察到归属于Fe/Fe相互作用的明显的g2.0 EPR信号。在催化（ +1.6 V vs. Ag/AgCl）电位下进行长时间的本体电解会导致[FeFe(μ-3-O)(μ-)] (H = 3,5-双(2-吡啶基)吡唑)中Fe中心的进一步氧化。通过这种电解达到稳态时，利用XANES和EXAFS拟合推断出高价Fe=O和Fe=O催化中间体的形成，检测到~1.6 Å处的短Fe=O键。[FeFe(μ-3-O)(μ-)] (H = 3,5-双(2-吡啶基)吡唑)被嵌入MIL-126金属有机框架中形成[FeFe(μ-3-O)(μ-)] (H = 3,5-双(2-吡啶基)吡唑)-MIL-126复合材料。后者在光电化学WOR中进行了测试，并在酸性（pH = 2）水溶液中可见光照射下表现出电催化电流的提高。所展示的光谱分析进一步深入了解了多核体系的催化途径，并应有助于随后开发基于地球上储量丰富金属的更具能量和成本效益的水分解催化剂。[FeFe(μ-3-O)(μ-)] (H = 3,5-双(2-吡啶基)吡唑)-MIL-126的光电催化活性证实了在固体载体内部创建[FeFe(μ-3-O)(μ-)] (H = 3,5-双(2-吡啶基)吡唑)组装体并通过太阳辐射增强其用于催化剂工业应用的可能性。
