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Energy crisis and global warming due to excessive CO2 emissions are the two major challenges of the world. Conversion of CO2 into useful fuels along with rechargeable metal air batteries and water ...

The top-down fabrication of catalytically active molecular metal oxide anions, or polyoxometalates, is virtually unexplored, although these materials offer unique possibilities, for catalysis, energy conversion and storage. Here, we report a novel top-down route, which enables the scalable synthesis and deposition of sub-nanometer molybdenum-oxo clusters on electrically conductive mesoporous carbon. The new approach uses a unique redox-cycling process to convert crystalline MoIVO2 particles into sub-nanometer molecular molybdenum-oxo clusters with a nuclearity of ∼1–20. The resulting molybdenum-oxo cluster/carbon composite shows outstanding, stable electrocatalytic performance for the oxygen reduction reaction with catalyst characteristics comparable to those of commercial Pt/C. This new material design could give access to a new class of highly reactive polyoxometalate-like metal oxo clusters as high-performance, earth abundant (electro-)catalysts., The top-down synthesis and deposition of polyoxometalate-like clusters on porous carbon is reported together with the high electrocatalytic oxygen reduction reactivity of the composite.

Defect engineering through heteroatom doping is one of the most important strategies towards the development of catalytic active materials for energy related applications. Herein, a novel trifunctional Br/Co/N Co-doped and defect-enriched porous carbon framework (BrHT@CoNC) is designed, which shows excellent electrocatalytic activity for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) as well as the hydrogen evolution reaction (HER). Introduction of extensive defects by heteroatom-doping is simply achieved by pyrolysis of the surfactant, dimethyldioctadecylammonium bromide (DODAB) modified ZIF-67. The BrHT@CoNC composite shows great potential as an economical catalyst/electrode for both rechargeable Zn–air batteries and overall water splitting devices. This work opens a new avenue toward the exploration of cost effective heteroatom doped catalysts for efficient integration of three or more functions into one freestanding electrode.

Polyoxometalate polymers with high proton conductivity are accessed for the first time by controlled covalent polymerization of Wells–Dawson-type niobotungstate and organoboronic acid monomers. The resulting polymer features a purely inorganic backbone, organic sidechains, and acts as a solid-state proton conductor. The controlled bottom‐up design of polymers with metal oxide backbones is a grand challenge in materials design, as it could give unique control over the resulting chemical properties. Herein, we report a 1D‐organo‐functionalized polyoxometalate polymer featuring a purely inorganic backbone. The polymer is self‐assembled from two types of monomers, inorganic Wells–Dawson‐type polyoxometalates, and aromatic organo‐boronates. Their covalent linkage results in 1D polymer strands, which combine an inorganic oxide backbone (based on B−O and Nb−O linkages) with functional organic side‐chains. The polymer shows high bulk proton conductivity of up to 1.59×10−1 S cm−1 at 90 °C and 98 % relative humidity. This synthetic approach could lead to a new class of organic–inorganic polymers where function can be designed by controlled tuning of the monomer units., publishedVersion

The development of scalable routes to highly active and efficient oxygen evolution reaction (OER) electrocatalysts based on earth-abundant materials is crucial for post-fossil fuel energy schemes. Here, we demonstrate how commercial copper foam electrodes can be functionalized for water oxidation using a facile electrodeposition process. The resulting composite electrode features hierarchically structured cobalt-iron-based catalyst particles, which offer channel-like structures for the transport of electrolyte and release of oxygen gas bubbles. We report high electrocatalytic OER performance as demonstrated by high current densities at low overpotentials (293 mV at j = 50 mA cm-2) and long-term stability under technologically relevant alkaline conditions (>24 h in 1.0 M aqueous KOH).

Single-atom electrocatalysts have attracted board interest in the recent years as they combine the advantages of heterogeneous and homogeneous electrocatalysts. Nevertheless, single-atom electrocatalysts with single metal component cannot further satisfy the demand of catalytic properties. This work developed atomic Co/Ni dual sites in N-doped porous carbon Janus-like frameworks through epitaxial growth of cobalt based MOFs on nickel complexes. Structural characterization and atomic-scale transmission electron microscopy revealed the homogeneously dispersed active sites of Co-Ni alloy and single Co/Ni atoms. Electrochemical data strongly demonstrated the advantages of integrating Co-MOF and Ni complex with different topological structures to form a Janus-like structure. The resultant catalysts afforded onset potential of 0.93 V and half-wave potential of 0.84 V for oxygen reduction reaction in alkaline media, and 0.86 V and 0.73 V in acid media, which is better than single noble-metal-free catalysts, even close to commercial Pt/C. Besides, the catalysts also exhibited good oxygen evolution reaction performance (a current density of 10 mA cm−2 at a potential of 1.59 V) and overvoltage between ORR and OER is 0.78 V. Density functional theory calculations indicated the high electrocatalytic activities are originated from the synergetic effect of atomic Co/Ni-N-C bonds and microstructure of the prepared materials. This work paves a new avenue for the development of multiatomic electrocatalysts for energy conversion.

We report a convergent, modular materials design strategy, which gives access to multifunctional metal oxide/carbon composites for high-performance electrocatalysis and electrochemical energy storage. The materials design uses the thermal conversion of a metal organic framework (ZIF-67) functionalized with molecular vanadium oxide clusters ([V10O28]6−) to give a nanostructured composite where redox-active crystalline Co–V–oxide nanoparticles (∼5 nm) are firmly embedded in a high surface-area N-doped graphitic carbon matrix. The composite shows high activity, efficiency and stability for the electrocatalytic oxygen evolution reaction in alkaline conditions. In addition, proof of concept studies show fast and reversible Li storage behavior. Based on this new materials design principle, the divergent fields of electrocatalysis and battery materials design could be linked to enable a more efficient, converging materials design approach.

In this study, three different Ag micro/nano leaves were successfully synthesized through a galvanic displacement reaction by adjusting the concentration of Ag+. The catalytic activities of the prepared Ag micro/nano leaves toward ORR showed strong dependence on their morphology. An optimal concentration of Ag+ can result in a well-defined Ag micro/nano leaves with both crystallization and surface area, which showed the best activity towards ORR in alkaline media. In addition, the prepared Ag micro/nano leaves also showed high activity towards CO2 reduction, which required a potential of -0.8 V versus RHE to selectively convert CO2 to CO with the faradaic efficiency at about 20%. Compared with the Ag plate at the same overpotential, the FE has increased by 5-fold.

Novel Co atoms immobilized carbon nanotubes (CoSAs@CNTs) are synthesized by structural engineering of the zeolitic imidazolate framework (ZIF-67) upon treatment with dicyandiamide (DCD). A unique morphology and promising electrochemical performance are shown by the Co atoms immobilized CNTs. The electrocatalyst remarkably exhibits a highly positive onset potential of 0.99 V and half-wave potential of 0.86 V, both even more positive than the commercial Pt/C catalyst, and the current density is also greater than that of the Pt/C catalyst in alkaline media. A decent performance is observed in acidic media also. The electrocatalyst is extraordinarily stable to harsh environments. A promising performance for the oxygen evolution reaction (OER) is demonstrated by the electrocatalyst, while for bifunctional electrocatalysis a small overvoltage of 0.78 V is observed with onset potential at the lower overpotential of 300 mV announcing the advantage of its usage for practical energy conversion and storage systems. ...

Earth‐abundant transition‐metal‐based catalysts for electrochemical water splitting are critical for sustainable energy schemes. In this work, we use a rational design method for the synthesis of ultrasmall and highly dispersed bimetallic CoMo carbide/oxide particles deposited on graphene oxide. Thermal conversion of the molecular precursors [H3PMo12O40], Co(OAc)2 ⋅4 H2O and melamine in the presence of graphene oxide gives the mixed carbide/oxide (Co6Mo6C2/Co2Mo3O8) nanoparticle composite deposited on highly dispersed, N,P‐doped carbon. The resulting composite shows outstanding electrocatalytic water‐splitting activity for both the oxygen evolution and hydrogen evolution reaction, and superior performance to reference samples including commercial 20 % Pt/C & IrO2. Electrochemical and other materials analyses indicate that Co6Mo6C2 is the main active phase in the composite, and the N,P‐doping of the carbon matrix increases the catalytic activity. The facile design could in principle be extended to multiple bimetallic catalyst classes by tuning of the molecular metal oxide precursor., A rational bottom‐up design method gives access to bimetallic metal carbide/oxide nanoparticles deposited on N,P‐doped carbon matrices. The resulting composites show outstanding electrochemical reactivity for oxygen and hydrogen evolution and allow the assembly of an overall water‐splitting device (see figure).

The electrochemical oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are two critical processes for energy conversion technologies, including water electrolysis, fuel cells, and metal-air batteries. For technological implementation, both reactions require highly active and stable electrocatalysts. Here, we report the simultaneous functionalization of carbon nanotubes with bimetallic manganese-vanadium OER/ORR catalytic sites, and nitrogen/sulfur atoms to increase electrical conductivity. A bottom-up fabrication route using polyoxometalate metal precursors enables facile and scalable deposition of bimetallic catalysts on the carbon nanotubes. Electrocatalytic OER/ORR studies show the high activity and stability of the composite under alkaline aqueous conditions, and comparable performance to commercial Pt/C (20 wt.%) was observed. Initial mechanistic analyses shed light on the effects of the bimetallic functionalization as well as the N/S-doping of the carbon nanotubes. In future, the use of heterometallic polyoxometalate precursors could allow the variation of metal types and atomic ratios, which could lead to well-defined bimetallic composites for various electrochemical processes.

Electrocatalytic water splitting into H2 and O2 is a key technology for carbon-neutral energy. Here, we report a modular materials design leading to noble metal-free composite electrocatalysts, which combine high electrical conductivity, high OER and HER reactivity and high durability. The scalable bottom-up fabrication allows the stable deposition of mixed metal oxide nanostructures with different functionalities on copper foam electrodes. The composite catalyst shows sustained OER and HER activity in 0.1 m aqueous KOH over prolonged periods (t>10 h) at low overpotentials (OER: ≈300 mV; HER: ≈100 mV) and high faradaic efficiencies (OER: ≈100 %, HER: ≈98 %). The new synthetic concept will enable the development of multifunctional, mixed metal oxide composites as high-performance electrocatalysts for challenging energy conversion and storage reactions.

A beneficial "microenvironment effect" on the efficiency of confined electrocatalysts is predicted by theory. However, examples of its experimental confirmation are scarce for catalysts based on polyoxometalates for the hydrogen evolution reaction (HER). For this purpose, the cyclic 48-tungsto-8-phosphate [H7P8W48O184](33) (P8W48) was fixed in a 3D configuration on reduced graphene oxide sheets (rGO) to boost its HER activity. The HRTEM imaging and the solid state P-31 NMR spectrum of P8W48/rGO reveal a strong interaction between individual P8W48 and transparent rGO sheets. The calculation of the interaction between P8W48 and graphene (G) sheets is difficult to perform within a reasonable period of time because of the large size and very high overall negative charge of P8W48. However, as P8W48 is symmetrical, a quarter of its structure [H2P2W12O48](12-) (P2W12) was extracted as a DFT calculation model. As P8W48 in P8W48/rGO is neutral, due to surrounding counter cations, the calculation model P2W12 is neutral with protons considering the affordable computational time. The adsorption energy for P2W12 on G (-1.55 eV) and the charge transfer between P2W12 and G (0.66 vertical bar e vertical bar) indicate that a strong interaction between P2W12 and G sheets exists. Kinetic studies show that the P8W48/rGO hybrids display excellent HER activity in acid, further confirmed by reproducible generation of hydrogen with quantitative faradaic yield and a high turnover frequency (11 s(-1) at 295 mV overpotential) for a noble metal-free electrocatalyst. Importantly, the overpotentials required for the HER compare well with those of the commercial Pt/C (20 wt% Pt), which indicates that P8W48/rGO is a promising cheap HER electrocatalyst. We demonstrate here the most convincing experimental evidence of the "microenvironment effect" on HER electrocatalysis by a polyoxometalate.

Ternary Ag nanoparticles (NPs)@polyoxometalate (POM)/reduced graphene oxide (rGO) nanohybrids were prepared by a facile photoreduction method, using POM as the photocatalyst, reducing and bridging molecules. The structure of the nanohybrids was characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy, etc. Most importantly, both the rotating disk electrode and rotating ring-disk electrode tests indicated that the Ag NPs@POM/rGO nanohybrids exhibited excellent electrocatalytic activity towards oxygen reduction reaction via a direct four-electron transfer pathway due to the synergistic effect of Ag NPs and rGO.

The green, facile, electrochemical-reduction-assisted assembly of ternary Ag nanoparticles (NPs)@polyoxometalate (POM)/reduced graphene oxide (rGO) is reported. The POM served as an electrocatalyst and bridging molecule. Characterization using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman and FT-IR spectroscopy analysis, etc., was performed and verified the structure of the prepared nanohybrids of Ag NPs@POM/rGO. The density and size of the Ag NPs on the rGO can be simply tuned by changing the concentration of Ag+. Most importantly, it is interesting to find that the ternary Ag NPs@POM/rGO nanohybrids showed much better electrocatalytic activities towards the oxygen reduction reaction than binary Ag NPs@POM and POM/rGO nanohybrids, and a direct four-electron transfer pathway was observed because of the synergistic effect of the Ag NPs and rGO. The electrocatalytic performance of Ag NPs@POM/rGO depended on the loading amount of Ag NPs, and 30% Ag NPs@POM/rGO showed the best electrocatalytic performance.

International audience; The application of nanohybrids based on polyoxomolybdates, reduced graphene oxide (rGO) and/or metal nanoparticles (NPs) high-performance electrode materials in electrocatalysis and energy storage devices is promising but still limited due to the complexity and the cost of the synthesis. Here we introduce a simple polyoxomolybdate, [Mo V 4O8(OH)2(H2O)2(C4O4)2] 2-(MoS), as reducing and stabilizing agent for the facile and one-pot syntheses of large quantity of highly stable MoS/rGO and MoS/Au NPs nanohybrids in aqueous solution without any catalyst or toxic co-solvent. They were characterized by various physical techniques and electrochemistry which confirm strong interaction between MoS and rGO sheets. We also used DFT calculations to investigate the affinity between MoS or its neutral form with graphene. The adsorption energy for the most stable configuration is-1.97 eV, indicating a strong adsorption process of MoS, which can also be confirmed by the distance (3.04 Å) and the charge transfer (0.86 e) between MoS and graphene. These observations are also consistent with the electrochemical results which underscore the excellent redox properties and high stability of MoS/rGO. Importantly, the MoS/rGO nanohybrids are excellent noble metal-free electrocatalysts for hydrogen peroxide reduction with high sensitivity, large detection range and low detection limit. Finally, the preliminary tests reveal that the electrode materials based on MoS/rGO and a low-cost carbon cloth (CC) composite MoS/rGO/CC may have a potential for an application in energy storage as performant and flexible supercapacitor, showing specific capacitance as high as 870 F g-1 at 10 mV s-1 and excellent stability after 5,000 cycles.

This work introduces facile synthetic methods of two new classes of green materials based on graphene (G) and the macrocyclic polyoxometalate [H7P8W48O184]33 (P8W48) alone or assembled with an imidazolium-based poly(ionic liquid) (PIL). The polyoxometalate serves as both an efficient graphite oxide reductant and a stabilizer. Owing to the strong adsorption of P8W48 on the resulting G sheets, water-dispersible P8W48@G hybrids were obtained without the need for surfactant or polymeric stabilizers. The P8W48@G hybrids were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and cyclic voltammetry. The presence of G in these hybrids induces an outstanding enhancement in the electrochemical properties of P8W48 in comparison with those observed with glassy carbon. Moreover, P8W48@G- and P8W48@PIL-G-based electrodes exhibit remarkable stability during prolonged potential cycling in various aqueous electrolytes. To the best of our knowledge, these are the first examples of successful syntheses of a high nuclearity polyoxometalate and graphene assemblies that might facilitate photoelectrocatalysis of multielectronic reactions.

A bottom-up method is used to construct novel metal-free catalysts for deeper study of oxygen reduction reaction (ORR) catalysis. Through controlling the structural evolution of a 2D covalent triazine-based framework, the conductivity, nitrogen configurations, and multidoping structures of the as-prepared catalysts can be easily tuned, which makes a great platform for both studying the mechanisms of the ORR and optimizing the performances of the metal-free catalysts.

A polyoxometalate (POM)-mediated green, facile and large-scale synthesis of 2D (2-dimensional) Ag NN/GNS nanohybrids (where NN stands for the nanonet and GNSs for graphene nanosheets) is reported. The synthesis is convenient, rapid and environmentally friendly. The POMs serve as reducing, encapsulating and bridging molecules, and avoid introducing any organic toxic molecules. The nanohybrids have been thoroughly characterized using SEM, EDX TEM, XRD, XPS and Raman spectroscopy. Most importantly, the nanohybrids were demonstrated to act as low cost catalysts for the oxygen reduction reaction in fuel cells with similar performance to Pt catalysts. We attribute it to the high catalytic activity of the Ag NN and the excellent electron transfer properties of GNSs and also their synergistic effect, being reinforced by the presence of molybdenum species on the Ag NN/GNS surface.

The well-defined metal NPs@POM–GNS tri-component nanohybrids were synthesized by a green, facile, one-pot method. The obtained nanohybrids exhibited exciting electrocatalytic activity for methanol and formic acid oxidation.

A simple solvothermal method has been used to synthesize novel double-shelled CeO2 hollow spheres (HSs) in a mixed solvent of PEG-400 and H2O. The structure and morphology of the CeO2 HSs were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption–desorption isotherms. The SEM and TEM images indicated that the as-prepared double-shelled CeO2 (about 400–500 nm in diameter) were aggregates of nanoparticles with sizes of about 15 nm. The shape and composition of the as-obtained products could be controlled by adjusting the ratio of PEG-400 and H2O in the solvothermal process. The effects of PEG-400/H2O ratio, solvothermal temperature and reaction time on the morphology evolution of as-prepared products were investigated, and the possible formation mechanism was proposed based on nucleation and the Ostwald ripening process as well as the soft-template function of PEG-400. In addition, the double-shelled CeO2 HSs show high electrocatalytic activity towards uric acid (UA) oxidation and thus exhibit good biosensor activities toward the detection of trace amounts of UA.

Two-dimensional CdS micro/nano leaves have been synthesized via a controlled hydrothermal process. The dimensions of the leaves is in the range of 4–6 μm and the thickness of the leaves is 30–50 nm. The surface of the leaves is smooth and composed of several parallel laminar layers with multi-steps. The SAED and HRTEM images indicated that the surface of the leaves was mainly composed of (0001) plane and all the leaves had single-crystallinity. The morphology of the as-prepared products could be controlled by adjusting the concentration of hydrofluoric acid (HF). The effects of HF concentration, reaction temperature and time were investigated. A possible formation mechanism is proposed based on the intrinsic crystal structure and selected adsorption processes. In addition, the as-prepared CdS pinnate leaves showed enhanced photocatalytic activity toward hydrogen evolution under visible light irradiation. The efficiency of micro/nano leaves was more than 6 times greater than normal CdS microparticles.

The facile, one-pot synthesis of Ag nanoparticle-decorated carbon nanotubes (CNTs) is reported. Polyoxometalates (POMs) were used to serve as both reducing and bridging molecules, which avoids the step of introducing other organic toxic molecules. Characterization using transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) analysis, etc. was performed and the structure of the prepared nanohybrid of Ag NPs@POM-CNTs was verified. The nanohybrid showed a high electrocatalytic activity towards oxygen reduction reaction because of the synergistic effect of Ag NPs and CNTs. The POM is removable in the nanohybrid without affecting the catalytic activities.