Keggin-type polyoxometalate anions [XM O ] are versatile, as their applications in interdisciplinary areas show. The Keggin anion [CoW O ] turns into an efficient and robust electrocatalyst upon its confinement in the well-defined void space of ZIF-8, a metal-organic framework (MOF). [H CoW O ]@ZIF-8 is so stable to water oxidation that it retains its initial activity even after 1000 catalytic cycles. The catalyst has a turnover frequency (TOF) of 10.8 mol O (mol Co) s , one of the highest TOFs for electrocatalytic oxygen evolution at neutral pH. Controlled experiments rule out the chances of formation and participation of CoO in this electrocatalyic water oxidation.

MOF based proton conductors have received immense importance recently. The present study endeavors to design two post-synthetically modified UiO-66 based MOFs and study the effects of their structural differences on their proton conductivity. UiO-66-NH 2 is modified by reaction with sultones to prepare two homologous compounds i.e., PSM 1 and PSM 2, which have SO 3 H groups in comparable extent (Zr:S ≈ 2: 1) in both. But the pendant alkyl chain holding the -SO3H group is of different length. PSM 2 has longer alkyl chain attachment than that of PSM 1. This difference in length of side arm results in huge difference in proton conducting behavior of the two compounds. PSM 1 is observed to have highest MOF based proton conductivity (1.64 × 10 -1 Scm -1 ) at 80 °C, which is comparable to commercially available Nafion while PSM 2 shows significantly lower conductivity. Again, the activation energy for proton conductivity is one of the lowest among all MOF based proton conductors in case of PSM 1 while, PSM 2 requires larger activation energy (almost three times).This profound effect of variation of chain length of side arm by 1 carbon atom in case of PSM 1 and PSM 2 was rather surprising and never documented before. This effect of length of side arm can be very useful to understand proton conduction mechanism of MOF based compounds and also to design better proton conductors. Besides, PSM 1 showed proton conductivity as high as 1.64 × 10 -1 Scm -1 at 80 °C temperature, which is the highest reported value till date among all MOF based systems. The lability of the -SO3H proton of the post synthetically modified UiO-66 MOFs has theoretically been determined by molecular electrostatic potential (MEP) analysis and theoretical pK a calculation of models of functional sites along with relevant NBO analyses.

Metal organic frameworks (MOFs) have received considerable importance as proton conducting materials in recent times. However, most of the MOFs lack the ability to form film, which limits their application. In the present work, polybenzimidazole (PBI) composite membranes have been prepared by loading post synthetically modified (PSM) UiO-66-NH 2 MOFs, denoted as PSM 1 and PSM 2 into an aryl ether-type polybenzimidazole (OPBI) polymer. The pristine OPBI, and MOF nanofiller loaded membranes were doped with phosphoric acid (PA) to prepare proton exchange membranes (PEMs). Use of thermally stable, hydrophilic MOFs resulted in enhanced proton conductivity, higher PA retention capacity, and increased stability against oxidative degradation for the composite membrane than the pristine OPBI polymer. The proton conductivities of the composite membranes (0.29 S cm −1 for PSM 1-10% and 0.308 S cm −1 for PSM 2-10% membranes at 160 °C, under anhydrous environment) were notably higher than the conductivities of the constituents and also higher than most of the MOF based polymer supported membranes. To the best of our knowledge, the PA doped PSM 2 loaded composite membrane shows the highest proton conductivity at 160 °C among all MOF based composite membranes. Extensive interfacial H-bonding plays the most crucial role behind the enhanced proton conductivities of the PA doped MOF containing polymer membranes reported here. This work clearly demonstrates the benefits of using rationally designed PSM 1 and PSM 2 MOFs as nanofiller to prepare OPBI supported membranes that can perform excellent proton conduction in a wide temperature range spanning up to 160 °C. This provides a generalized approach toward achieving an efficient proton conducting membrane for use in fuel cells.

A polyoxometalate (POM)-supported nickel(II) coordination complex, [Ni(2,2'-bpy)][{Ni(2,2'-bpy)(HO)}{HCoWO}]·3HO (1; 2,2'-bpy = 2,2'-bipyridine), has been synthesized and structurally characterized. We could obtain a relatively better resolved structure from dried crystals of 1, Ni(2,2'-bpy)][{Ni(2,2'-bpy)(HO)}{HCoWO}]·HO (D1). Because the title compound has been characterized with a {Ni(2,2'-bpy)(HO)} fragment coordinated to the surface of the Keggin anion ([H(CoWO]) via a terminal oxo group of tungsten and the [Ni(2,2'-bpy)] coordination complex cation sitting as the lattice component in the concerned crystals, the electronic spectroscopy of compound 1 has been described by comparing its electronic spectral features with those of [Ni(2,2'-bpy)(HO)Cl]Cl, [Ni(2,2'-bpy)]Cl, and K[CoWO]·6HO. Most importantly, compound 1 can function as a heterogeneous and robust electrochemical water oxidation catalyst (WOC). To gain insights into the water oxidation (WO) protocol and to interpret the nature of the active catalyst, diverse electrochemical experiments have been conducted. The mode of action of the WOC during the electrochemical process is accounted for by confirmation that there was no formation/participation of metal oxide during various controlled experiments. It is found that the title compound acts as a true catalyst that has Ni (coordinated to POM surface) acting as the active catalytic center. It is also found to follow a proton-coupled electron-transfer pathway (two electrons and one proton) for WO catalysis with a high turnover frequency of 18.49 (mol of O)(mol of Ni) s.

Electrochemically active Metal-Organic Frameworks (MOFs) have been progressively recognized for their use in solar fuel production schemes. Typically, they are utilized as platforms for heterogeneous tethering of exceptionally large concentration of molecular electrocatalysts onto electrodes. Yet so far, the potential influence of their extraordinary chemical modularity on electrocatalysis has been overlooked. Herein, we demonstrate that, when assembled on a solid Ag CO 2 reduction electrocatalyst, a non-catalytic UiO-66 MOF acts as a porous membrane that systematically tunes the active sites immediate chemical environment, leading to a drastic enhancement of electrocatalytic activity and selectivity. Electrochemical analysis shows that the MOF membrane improves catalytic performance through physical and electrostatic regulation of reactants delivery towards the catalytic sites. The MOF also stabilizes catalytic intermediates via modulation of active sites secondary coordination sphere. This concept can be expanded to a wide range of proton-coupled electrochemical reactions, providing new means for precise, molecularlevel manipulation of heterogeneous solar fuels systems.

Keggin-type polyoxometalate anions [XM 12 O 40 ] nÀ are versatile,a st heir applications in interdisciplinary areas show.T he Keggin anion [CoW 12 O 40 ] 6À turns into an efficient and robust electrocatalyst upon its confinement in the welldefined void space of ZIF-8, am etal-organic framework (MOF). [H 6 CoW 12 O 40 ]@ZIF-8 is so stable to water oxidation that it retains its initial activity even after 1000 catalytic cycles. The catalyst has at urnover frequency (TOF) of 10.8 mol O 2 (mol Co) À1 s À1 ,o ne of the highest TOFs for electrocatalytic oxygen evolution at neutral pH. Controlled experiments rule out the chances of formation and participation of CoO x in this electrocatalyic water oxidation.Photosynthesis,one of the most fundamental and essential processes to sustain life on earth, works on the principle of trapping solar energy via electron-hole pair formation. [1,2] This energy is ultimately utilized in splitting of water molecules into H 2 and O 2 .W ater splitting (WS) has emerged as apromising source of clean and sustainable energy. [3] Water oxidation (WO; 2H 2 O!4H + + O 2 + 4e À ; E 0 = 1.23 V), being the bottleneck process of WS owing to its high thermodynamic potential and high overpotential h,requires an efficient and stable WO catalyst (WOC). [4,5] In last few decades, various research groups have contributed towards understanding of the process of WO and designing of robust and efficient WOCs. [1][2][3][4][5][6][7] Recently enormous efforts have been devoted to prepare first-row transition-metal-ion (particularly,c obalt)-based inexpensive WOCs. [8][9][10][11][12][13][14][15][16][17][18] Development of polyoxometalates (POMs) as WOCs came as am ajor breakthrough in this regard. [19][20][21][22][23][24][25][26][27] Thek ey structural features of POMs for POM-WOCs are their complete inorganic skeleton and the scope of fast, reversible electron transfer (resulting into fast WO kinetics). [14,28] In last few years,a long with remarkable progress in this field, questions also arose about the true catalyst species (formation and participation of CoO x as true catalyst). [28][29][30][31][32] Meanwhile,H ill, Geletii, and their coworkers [23] confirmed that their starting Co-POM compound [Co 4 (H 2 O) 2 (a-PW 9 O 34 ) 2 ] 10À was atrue molecular WO catalyst (not CoO x ). Keggin-type POMs have the general formula of [XM 12 O 40 ] nÀ (X = Co 2+ ,P 5+ ,S i 4+ ,e tc.;M= W 6+ ,M o 6+ ,e tc.) and are the most stable structural variant among all POMs. [33][34][35][36] Despite ac onsiderable development in the field of POM-WOC,n ot much attention has been paid to Keggin (as such)-WOC systems as most of them do not possess suitable WOC-active site (unless it has one or more substitution of Mb yaWO-active transition-metal ion). [28,[37][38][39] Recently,S ong et al. [37] showed K 6 [CoW 12 O 40 ]t ob ei nactive to photocatalytic WO,w hile K 7 [Co III Co II (H 2 O)W 11 O 39 ], was found to be active owing to ap eripheral Co III -aqua coordination complex. We thus made an attempt to prepare WOC from [CoW 12 ...

An efficient and robust heterogeneous electrocatalyst, FSWZ-8 ((Fe-(salen)(OH) + H 4 [SiW 12 O 40 ]•HCl)@ZIF-8) for oxygen evolution reaction (OER) at the neutral pH, was developed by coencapsulation of Fe-salen (i.e., Fe(salen)Cl) and SiW 12 (i.e., H 4 [SiW 12 O 40 ]) inside the cavity of zeolitic imidazolate framework-8 (ZIF-8) material by an in situ synthesis. Here ZIF-8 functions as a host, Fe-salen as the active catalyst, and SiW 12 helps in the charge transport by lowering the overall electrical resistance of the resulting composite system. High turnover frequency (∼5 s −1 ) and high Faradaic efficiency (∼94%) make the concerned composite an efficient catalyst toward water oxidation. This is the first report of one of the simplest known metal complexes, Fe-salen, to perfrom electrocatalytic OER as a heterogeneous catalyst in the neutral pH. This work also highlights the benefits of coencapsulation of the Keggin polyoxometalate (POM) along with the active catalyst Fe-salen species. Encapsulation of SiW 12 results in (i) faster formation of FSWZ-8 composite, (ii) higher loading of Fe-salen, and, most importantly, (iii) lowering of required overpotential for electrochemical OER by more than 150 mV. The Keggin POMs, located as discrete molecular oxides inside the cavity of ZIF-8 as well as on the surface of ZIF-8, facilitate electrical charge conduction in the ZIF-8 matrix and lower the overall charge-transfer resistance.

In recent years, we are witnessing a substantially growing scientific interest in MOFs and their derived materials in the field of electrocatalysis. MOFs acting as a self-sacrificing template offer various advantages for the synthesis of carbon-rich materials, metal oxides, and metal nanostructures containing graphitic carbon-based materials benefiting from the high surface area, porous structure, and abundance of metal sites and organic functionalities. Yet, despite recent advancement in the field of MOF-derived materials, there are still several significant challenges that should be overcomed, to obtain better control and understanding on the factors determining their chemical, structural and catalytic nature. In this minireview, we will discuss recently reported advances in the development of promising methods and strategies for the construction of functional MOF-derived materials and their application as highly-active electrocatalysts for two important energy-related reactions: nitrogen reduction to produce ammonia, and CO2 reduction into carbon-based fuels. Moreover, a discussion containing assessments and remarks on the possible future developments of MOF-derived materials toward efficient electrocatalysis is included.