Howe Andrew, Liseev Timofey, Gil-Sepulcre Marcos, Gimbert-Suriñach Carolina, Benet-Buchholz Jordi, Llobet Antoni, Ott Sascha
Department of Chemistry - Ångström Laboratory, Uppsala University, Box 523 75120 Uppsala Sweden
Institute of Chemical Research of Catalonia (ICIQ), Barcelona Institute of Science and Technology (BIST) Av. Països Catalans 16 43007, Tarragona Spain.
Mater Adv. 2022 Apr 5;3(10):4227-4234. doi: 10.1039/d2ma00128d. eCollection 2022 May 23.
A novel tetratopic metallo-linker, [Ru(tda)(py(PhCOOH))], 1, (tda = 2,2':6',2''-terpyridine-6,6''-dicarboxylate; py(PhCOOH) = (4,4'-(pyridine-3,5-diyl)dibenzoic acid), that is structurally based on one of the most active molecular water oxidation catalysts has been prepared and fully characterized, including single crystal X-ray diffraction. 1 bears geometric similarities to HTBAPy (HTBAPy = 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetrabenzoic acid), the native linker in NU-1000, which offers the possibility to synthesize NU-1000-Ru mixed linker MOFs solvothermally. Mixed linker MOF formation was demonstrated by powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM), and Ru linker incorporation confirmed by FT-IR, energy-dispersive X-ray (EDX) spectroscopy and inductively coupled plasma optical emission spectroscopy (ICP-OES). It was found that the Ru contents in the final mixed linker MOFs correlate with the amount of Ru linker present during solvothermal synthesis, albeit not in a linear fashion. The cyclic voltammograms (CV) of the mixed linker MOFs are largely dominated by TBAPy-based oxidations with features attributed to 1. Interestingly, Ru linkers near the crystal surface are oxidized directly by interfacial hole transfer form the electrode, while those in the crystal interior can be oxidized indirectly from oxidized TBAPy linkers at more anodic potential. Upon repeated scanning, the CVs show the appearance of new waves that arise from irreversible TBAPy oxidation, as well as from the activation of the Ru-based water oxidation catalyst. Of the materials prepared, the one with the highest Ru content, NU-1000-Ru, was shown to catalyze the electrochemical oxidation of water to dioxygen. The Faradaic efficiency (FE) of the construct is 37%, due to water oxidation being accompanied by oxidative transformations of the TBAPy linkers. Despite the low FE, NU-1000-Ru is still among the best MOF-based water oxidation catalysts, operating by a unique co-linker mediated hole-transport mechanism to supply oxidizing equivalents also to catalysts in the crystal interior.
一种新型的四齿金属连接体[Ru(tda)(py(PhCOOH))]，即1（tda = 2,2':6',2''-三联吡啶-6,6''-二羧酸；py(PhCOOH) = (4,4'-(吡啶-3,5-二基)二苯甲酸），已被制备并通过单晶X射线衍射等手段进行了全面表征。该连接体在结构上基于最具活性的分子水氧化催化剂之一。1与HTBAPy（HTBAPy = 4,4',4'',4'''-(芘-1,3,6,8-四基)四苯甲酸）具有几何相似性，HTBAPy是NU-1000中的天然连接体，这为溶剂热合成NU-1000-Ru混合连接体金属有机框架提供了可能性。通过粉末X射线衍射（PXRD）和扫描电子显微镜（SEM）证明了混合连接体金属有机框架的形成，并通过傅里叶变换红外光谱（FT-IR）、能量色散X射线（EDX）光谱和电感耦合等离子体发射光谱（ICP-OES）确认了Ru连接体的掺入。研究发现，最终混合连接体金属有机框架中的Ru含量与溶剂热合成过程中存在的Ru连接体的量相关，尽管并非呈线性关系。混合连接体金属有机框架的循环伏安图（CV）在很大程度上由基于TBAPy的氧化主导，具有归因于1的特征。有趣的是，晶体表面附近的Ru连接体通过电极的界面空穴转移直接被氧化，而晶体内部的Ru连接体在更高的阳极电位下可由氧化的TBAPy连接体间接氧化。在重复扫描时，CV显示出由不可逆的TBAPy氧化以及基于Ru的水氧化催化剂的活化产生的新波的出现。在所制备的材料中，Ru含量最高的材料NU-1000-Ru被证明能催化水的电化学氧化生成氧气。该结构的法拉第效率（FE）为37%，这是因为水氧化伴随着TBAPy连接体的氧化转化。尽管FE较低，但NU-1000-Ru仍然是最好的基于金属有机框架的水氧化催化剂之一，它通过独特的共连接体介导的空穴传输机制运行，也为晶体内部的催化剂提供氧化当量。
