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Insights into the directions to increase turnover frequency and turnover number during photochemical water oxidation with molecular Ru catalysts
Energy & Environmental Science ( IF 32.5 ) Pub Date : 2022-08-19 , DOI: 10.1039/d2ee01128j
Indira Pokhrel , Dinneswara Reddy Guda , Taejin Kwon , Eungyeong Choi , Yu Sung Chun , Sang Tak Lee , Bong June Sung , Duck-Hyung Lee , Han Bin Oh , Kyung Byung Yoon

A series of four mononuclear water oxidation catalysts (WOCs), denoted as [A2Tpz–RuII], in which A2 represents two axial monodentate ligands, pyridine (Pyr), 4-picoline (4-Pic), isoquinoline (Iqn), and N-methyl imidazole (Imd), and Tpz represents a planar tetradentate ligand in the equatorial position (6,6′-di(1H-pyrazol-1-yl)-2,2′-bipyridine) were prepared. A series of four photosensitizers (PSs), [Ru(bpy)3]2+, [Ru(bpy)2{bpy-(CO2Et)2}]2+, [Ru(bpy){bpy-(CO2Et)2}2]2+, and [Ru{bpy-(CO2Et)2}3]2+, where bpy and bpy-(CO2Et)2 denote 2,2′-bipyridine and diethyl [2,2′-bipyridine]-4,4′-dicarboxylate, respectively, denoted as [PS-n]2+, where n = 0, 2, 4, and 6, were prepared. The three known WOCs with the related structures were also prepared. The catalytic performances of the above seven WOCs were evaluated in terms of turnover frequencies (TOFs) and turnover numbers (TONs), while varying PS, and their performances were compared. The measured TOFs were much smaller than those chemically measured. The low concentration of auxiliary oxidant, [PS-n]3+, arising from low photon flux density of the incident solar simulated light is proposed to be responsible for the large decrease in TOFs. The oxidation power of the oxidized form of [PS-n]2+ ([PS-n]3+), the oscillator strength (f) of [PS-n]2+ and the lifetime of the [PS-n]2+ in the excited state (τps*) also sensitively affect the catalytic performance of a WOC. The results were also analyzed by the reaction schemes that were widely used for mononuclear Ru-based WOCs. For this, the corresponding energy-minimized structures, the energy levels of highest occupied molecular orbitals of the initially added WOCs and intermediates, and the free energy change (ΔG°) for each reaction step were also derived from DFT calculations. This work introduces a new promising series of WOCs, and gives insights into the directions to increase TONs and TOFs during photochemical evaluations of WOCs.

中文翻译:

分子钌催化剂在光化学水氧化过程中提高周转频率和周转数的方向

一系列四种单核水氧化催化剂(WOCs),记为[A 2 T pz –Ru II ],其中A 2代表两个轴向单齿配体,吡啶(Pyr)、4-甲基吡啶(4-Pic)、异喹啉( Iqn) 和N-甲基咪唑 (Imd),T pz代表平面四齿配体在赤道位置 (6,6'-di(1 H -pyrazol-1-yl)-2,2'-bipyridine)准备好了。一系列四种光敏剂(PSs),[Ru(bpy) 3 ] 2+ , [Ru(bpy) 2 {bpy-(CO 2 Et) 2 }] 2+ , [Ru(bpy){bpy-(CO 2等)2} 2 ] 2+和 [Ru{bpy-(CO 2 Et) 2 } 3 ] 2+,其中 bpy 和 bpy-(CO 2 Et) 2表示 2,2'-联吡啶和二乙基 [2,2'-联吡啶]-4,4'-二羧酸盐,分别表示为 [PS- n ] 2+,其中n= 0、2、4 和 6,已准备好。还制备了具有相关结构的三种已知WOC。对上述七种WOCs的催化性能进行了评估,并根据转换频率(TOFs)和转换次数(TONs),同时改变了PS,并比较了它们的性能。测量的 TOF 比化学测量的要小得多。由入射太阳模拟光的低光子通量密度引起的低浓度辅助氧化剂 [PS- n ] 3+被认为是 TOF 大幅下降的原因。[PS- n ] 2+ ([PS- n ] 3+ )的氧化形式的氧化能力,[PS-的振荡器强度 ( f )n ] 2+和[PS- n ] 2+在激发态的寿命(τ ps*)也敏感地影响WOC的催化性能。还通过广泛用于单核钌基 WOC 的反应方案分析了结果。为此,相应的能量最小化结构、最初添加的 WOCs 和中间体的最高占据分子轨道的能级以及每个反应步骤的自由能变化 ( ΔG °) 也来自 DFT 计算。这项工作介绍了一系列新的有前途的 WOC,并为在 WOC 的光化学评估过程中增加 TON 和 TOF 的方向提供了见解。
更新日期:2022-08-19
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