A Forceful "Dendrite-Killer" of Polyoxomolybdate with Reusability Effectively Dominating Dendrite-Free Lithium Metal Anode.

In this work, a series of Mo-containing polyoxometalates (POMs) modified separators to inhibit the growth of lithium dendrites, and thus improving the lifespan and safety of the cells is proposed. When the deposited lithium forms dendrites and touches the separator, the optimized Dawson-type POM of (NH4 )6 [P2 Mo18 O62 ]·11H2 O (P2 Mo18 ) with the stronger oxidizability, acts like a "killer", is more inclined to oxidize Li0 into Li+ , thus weakening the lethality of lithium dendrites. The above process is accompanied by the formation of Lix [P2 Mo18 O62 ] (x = 6-10) in its reduced state. Converting to the stripping process, the reduced state Lix [P2 Mo18 O62 ] (x = 6-10) can be reoxidized to P2 Mo18 , which achieves the reusability of P2 Mo18 functional material. Meanwhile, lithium ions are released into the cell system to participate in the subsequent electrochemical cycles, thus the undesired lithium dendrites are converted into usable lithium ions to prevent the generation of "dead lithium". As a result, the Li//Li symmetrical cell with P2 Mo18 modified separator delivers exceptional cyclic stability for over 1000 h at 3 mA cm-2 and 5 mAh cm-2 , and the assembled Li-S full cell maintains superior reversible capacity of 600 mAh g-1 after 200 cycles at 2 C.

Substituent Effect to Fine-Tune Energy Levels of Atom-Precise [MoOS3 ]2- Modified Copper(I) Thiolate Clusters Boosting Recyclable Photocatalysis.

The propulsion of photocatalytic hydrogen (H2 ) production is limited by the rational design and regulation of catalysts with precise structures and excellent activities. In this work, the [MoOS3 ]2- unit is introduced into the CuI clusters to form a series of atomically-precise MoVI -CuI bimetallic clusters of [Cu6 (MoOS3 )2 (C6 H5 (CH2 )S)2 (P(C6 H4 -R)3 )4 ] ⋅ xCH3 CN (R=H, CH3 , or F), which show high photocatalytic H2 evolution activities and excellent stability. By electron push-pull effects of the surface ligand, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of these MoVI -CuI clusters can be finely tuned, promoting the resultant visible-light-driven H2 evolution performance. Furthermore, MoVI -CuI clusters loaded onto the surface of magnetic Fe3 O4 carriers significantly reduced the loss of catalysts in the collection process, efficiently addressing the recycling issues of such small cluster-based catalyst. This work not only highlights a competitively universal approach on the design of high-efficiency cluster photocatalysts for energy conversion, but also makes it feasible to manipulate the catalytic performance of clusters through a rational substituent strategy.

Enhanced catalysis of a vanadium-substituted Keggin-type polyoxomolybdate supported on the M3O4/C (M = Fe or Co) surface enables efficient and recyclable oxidation of HMF to DFF.

In the reaction of oxidizing 5-hydroxymethylfurfural (HMF), attaining high efficiency and selectivity in the conversion of HMF into DFF presents a challenge due to the possibility of forming multiple products. Polyoxometalates are considered highly active catalysts for HMF oxidation. However, the over-oxidation of products poses a challenge, leading to decreased purity and yield. In this work, metal-organic framework-derived Fe3O4/C and Co3O4/C were designed as carriers for the vanadium-substituted Keggin-type polyoxomolybdate H5PMo10V2O40·35H2O (PMo10V2). In this complex system, spinel oxides can effectively adsorb HMF molecules and cooperate with PMo10V2 to catalyze the aerobic oxidation of HMF. As a result, the as-prepared PMo10V2@Fe3O4/C and PMo10V2@Co3O4/C catalysts can achieve efficient conversion of HMF into DFF with almost 100% selectivity. Among them, PMo10V2@Fe3O4/C exhibits a higher conversion rate (99.1%) under milder reaction conditions (oxygen pressure of 0.8 MPa). Both catalysts exhibited exceptional stability and retained their activity and selectivity even after undergoing multiple cycles. Studies on mechanisms by in situ diffuse reflectance infrared Fourier transform spectroscopy and X-ray photoelectron spectroscopy revealed that the V5+ and Mo6+ in PMo10V2, together with the metal ions in the spinel oxides, act as active centers for the catalytic conversion of HMF. Therefore, it is proposed that PMo10V2 and M3O4/C (M = Fe, Co) cooperatively catalyze the transformation of HMF into DFF via a proton-coupled electron transfer mechanism. This study offers an innovative approach for designing highly selective and recyclable biomass oxidation catalysts.

Graphene-supported polyoxometalate entrapped in a MIL-88A network with highly efficient conversion of polysulfides in Li-S batteries.

It has been demonstrated that polyoxometalates (POMs) have strong anchoring abilities with efficient catalysis of lithium polysulfides (LiPSs). However, the severe aggregation that buries the effective active sites of POMs along with poor electrical conductivity limits the practical application of POMs in lithium sulfur batteries (LSBs). In our strategy, we utilized reduced graphene oxide (rGO) to support a POM catalyst entrapped in a MIL-88A(FeCo) network with a hollow shell skeleton as the sulfur host material. H4PW11VO40 (PW11V) with optimal vanadium atom implantation ensures the ruggedness and integrity of the hollow structure, which is conducive to achieving high sulfur loading as well as accommodating the volume change of the sulfur cathode during the charging and discharging process. Importantly, PW11V can capture polysulfides through firm chemical adsorption and accelerate redox reactions of LiPS conversion by effective electrochemical catalysis. Furthermore, the satisfactory electrical conductivity of rGO provides access for electrons to reach the interface of PW11V and polysulfides and trigger Li-S conversion reactions. Thus, the constructed PW11V-based sulfur cathode exhibited a superior specific capacity of 905 mA h g-1 after 100 cycles under 0.2 C and long cycling life with a capacity recession rate of 0.046% for each cycle upon 500 cycles under 3 C. This research reveals the effect of vanadium atom substitution of POMs on the cycling performance of a sulfur cathode and affords insight for developing high-performance LSBs.

Manipulation of the MoO2/MoSe2 Heterointerface Boosting High Rate and Durability for Sodium/Potassium Storage.

The main challenge for sodium/potassium ion storage is to find the suitable host materials to accommodate the larger-sized Na+/K+ and conquer the sluggish chemical kinetics. Herein, by selenation of polyoxometalate in electrospinning fiber, a novel MoO2/MoSe2 heterostructure embedded in one-dimensional (1D) N,P-doped carbon nanofiber (MoO2/MoSe2@NPC) is rationally constructed to show distinct enhancement of rate performance and cycle life for sodium ion batteries (SIBs) and potassium ion batteries (PIBs). The 1D skeleton of MoO2/MoSe2@NPC decreases the diffusion pathway of Na+/K+, and the doping of N/P heteroatoms in carbon fiber creates abundant active sites and provides good reachability for Na+/K+ transportation. MoSe2 nanosheets grow in the bulk phase of MoO2 via in situ local phase transformation to achieve effective and firm heterointerfaces. Especially, the exposure extent of heterointerfaces can be controlled by treatment temperature during the preparation process, and the optimized heterointerfaces result in an ideal synergic effect between MoO2 and MoSe2. DFT calculations confirm that the internal electric field in the heterogeneous interface guides the electron transfer from MoO2 to MoSe2, combined with strong adsorption capacity toward sodium/potassium, facilitating ion/electron transfer kinetics. It is confirmed that the MoO2/MoSe2@NPC anode for SIBs delivers 382 mA h g-1 under 0.1 A g-1 upon 200 cycles; meanwhile, a reversible capacity of 266 mA h g-1 is maintained even under 2 A g-1 after 2000 cycles. For PIBs, it can reach up to 216 mA h g-1 in the 200th cycle and still retain 125 mA h g-1 after 2000 cycles under 1 A g-1. This study opens up a new interface manipulation strategy for the design of anode materials to boost fast Na+/K+ storage kinetics.

A 20-core copper(I) nanocluster as electron-hole recombination inhibitor on TiO2 nanosheets for enhancing photocatalytic H2 evolution.

For the design of atom-precise copper nanoclusters, besides the exploration of their aesthetic cage-like architectures, their structural modulation and potential applications are being extensively explored. Herein, an atom-precise 20-core copper(I)-alkynyl nanocluster (UJN-Cu20) protected by ethinyloestradiol ligands issynthesized. By virtue of outer-shell hydroxyl groups, UJN-Cu20 could be uniformly modified on the surface of TiO2 nanosheets via hydrogen bonding interactions, thus forming an efficient nanocomposite photocatalyst for hydrogen evolution. By constructing a Z-scheme heterojunction, the photocatalytic hydrogen evolution activity of the nanocomposite (13 mmol g-1 h-1) significantly improved as compared to that of TiO2 nanosheets (0.4 mmol g-1 h-1). As a narrow bandgap cocatalyst, UJN-Cu20 is confirmed to effectively inhibit the electron-hole recombination on the surface of the TiO2 nanosheet, which provides a new concept for the design of copper cluster-assisted effective photocatalysts.

Pt-Substituted polyoxometalate modification on the surface of low-cost TiO2 with highly efficient H2 evolution performance.

In this study, Pt-substituted polyoxometalate was first modified on the surface of commercially available TiO2, forming an efficient photocatalyst with high reactivity for hydrogen evolution. During the photocatalytic process, Pt-polyoxometalates not only increase the mobility rate of electrons but also improve the separation efficiency of photoinduced electrons and holes. After photoreduction, the in situ generated Pt0 species are anchored on the surface of polyoxometalate anion, which prevents further agglomeration. Then, the in situ formed Pt0 species and polyoxometalates synergistically promote the efficiency of photoinduced electron transfer from TiO2 to the protons adsorbed on the Pt0 surface. Although the content of Pt0 in the nanocomposite is only 0.6%, the photocatalytic hydrogen production rate reaches 5.6 mmol g-1 h-1 and remains stable at 4.5 mmol g-1 h-1 after the continuous catalytic process. Due to the modification of TiO2 by Pt-substituted polyoxometalate, this nanocomposite represents a practical model that possesses highly efficient photoelectric conversion performance. The presented work not only extends the family of new TiO2-polyoxometalate-based materials but also takes a further step toward the practical application of commercial TiO2 in photocatalytic hydrogen production.