Keplerate-type polyoxometalates represent a large series of high nuclear molecular clusters; for example, (NH ) [Mo Mo O (CH COO) (H O) ] ({Mo }) is a kind of spherical heteropoly blue with a large overall negative charge and an electron density and topological structure similar to C . {Mo } is a good bifunctional material that can be used as an electron acceptor or donor, which is advantageous to accelerate electron transmission in supercapacitors. Herein, a nanocomposite of rGO functionalized with a Keplerate-type polyoxometalate {Mo } was prepared by a facile chemical reduction method and used to construct supercapacitors for the first time. The electrochemical performance of the supercapacitors can be significantly improved due to the excellent redox properties, high electronegativity, and hollow porous structures of {Mo }, in addition to the outstanding conductivity of rGO. The {Mo }-rGO nanocomposite electrode exhibited an excellent gravimetric specific capacitance of 617.3 F g at a current density of 5 A g in 1 m Li SO electrolyte. An aqueous asymmetric supercapacitor with a voltage range of 2.1 V, with the {Mo }-rGO nanocomposite as the negative electrode and modified activated carbon as the positive electrode, exhibited a high energy density of 31.6 Wh kg with a power density of 207.7 W kg and favorable cycling stability.

which should have wide spectrum absorptions, anchoring groups, and appropriate energy levels in order to absorb more sunlight and excite the ground-state electrons to the excited state, then inject into the semiconductor conduction band, while the holes remain in the dye molecule form the charge separations, which ensure the effective regenerations of the photosensitizers and the unidirectional electron injections. [2] In recent decades, great efforts have been made to develop the photosensitizers with high stability, low-cost, and high solar energy conversion in the fields of photocatalysts and solar cells. [3,4] However, developing broad-spectrum photosensitizers is still a big challenge. At present, the commonly used photosensitizers including ruthenium-pyridine, porphyrin, and pure organic dyes, have efficiently improved the power conversion efficiencies (PCEs) of the DSSCs. [5] However, their large-scale productions and applications in photovoltaic industry have been limited by their high costs and the cumbersome process in the synthesis and purification of photosensitizers. [6] Furthermore, the defects of some photosensitizers in spectral absorption also restrict the utilization of sunlight. So, it is urgent to develop the photosensitizers with environment-friendly, simple preparations, low costs, and wide spectra absorptions.Heteropoly blues (HPBs) is a reductive state of polyoxometalates (POMs representing oxidation state) with fascinating structures, abundant element compositions, reversible redox properties, and wide pH stability. [7,8] The advantages of HPBs as photosensitizer are as follows: i) their wide and strong spectral absorptions in visible and near-IR regions; ii) the anchoring groups are easily to coordinated to HPBs to firmly adsorb on the semiconductor surface; iii) their energy levels involving the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) can be adjusted by the composition, structure, and charge density to ensure the effective unidirectional electron injections and photosensitizer regenerations; [9] iv) their excellent light, thermal and electrochemical stability, their ability to accept or lose "blue" electrons without any structural transformations. As a kind of the potential photosensitizer candidates, HPBs have been increasingly recognized in terms of photocatalysis and solar cells. [10][11][12][13][14] However, the instability of HPBs in the air restricts the further research of their photosensitivity and their use as the photosensitizers in DSSCs.The photosensitizer is the soul of dye-sensitized solar cells (DSSCs), i.e., the key factor influencing the performance of DSSCs. The commonly used photo sensitizers are expensive carboxylic pyridine ruthenium-based complexes, so it is urgent to develop low-cost photosensitizers. Heteropoly blues (HPBs) could be a kind of excellent photosensitizers due to their wide spectra absorption; however, most of them are hardly stable in the air. Here, a strategy of combining the improved vacuum...

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Polyoxometalates (POM) have already been confirmed to act as effective electron-transfer mediators for improving the power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs) based on previous studies. However, the improvement may be limited by the agglomeration of the polyoxoanions. In this paper, the previous synthesis strategy is improved upon by breaking the metal-organic frameworks (MOFs) with POMs as the secondary building units ([Ni(bpp)(H O) ] [P W O ]⋅24 H O (1) (bpp=1,3-bis(4-pyridyl)propane) and H [Cu (H O) (P W O ) (3-dpye) ]⋅28 H O (2) (3-dpye=N,N'-bis(3-pyridinecarboxamide)-1,2-ethane)) to design and synthesize small sized and highly disperse POM nanoparticles by means of compositing with TiO , through calcination to remove the organic ligand. TEM and element mapping confirm that P W O (denoted as P W ) nanoparticles with the diameter of ≈1 nm are uniformly distributed in TiO composites. The loading amount (wt. %) of POM in MOFs reaches 75.67 %. The small sized and highly disperse P W nanoparticles may provide more active sites and specific surface areas for improving the PCE of DSSCs. Finally, the investigations indicate that the PCE of composite P W ⋅NiO@TiO photoanodes is up to 7.56 %, which was 26 % higher than the pristine TiO based photoanodes.

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The design and development of efficient and stable nonprecious-metal-based catalysts for counter electrodes (CEs) in dye-sensitized solar cells (DSSCs) has received a great deal of attention. In this work, molybdenum carbide nanoparticles homogeneously distributed in a nitrogen-rich carbon matrix (Mo C@NC) have been synthesized from inexpensive raw materials (polyoxometalate and dicyandiamide) by a facile one-step solid-phase synthesis method. The novel Mo C@NC hybrid was not only used as a CE in a DSSC, but also showed superior catalytic activity towards I /I as a redox electrolyte. The power conversion efficiency of a DSSC with Mo C@NC as the CE was as high as 6.49 %, comparable to that with Pt (6.38 %). The CE was prepared by a drop-coating method, without the addition of another conductive polymer. Most importantly, the method circumvents the problem of the sample falling off from the fluorine-doped tin oxide (FTO), and the CE could be repeatedly reused with unchanged efficiency. Therefore, it opens the way for the development of platinum-free catalysts with low cost, simple processing, good stability, and high efficiency.