Strategic Design of a Bifunctional NiFeCoW@NC Hybrid to Replace the Noble Platinum for Dye-Sensitized Solar Cells and Hydrogen Evolution Reactions

Designing a hybrid nanomaterial based on Cr-containing polyoxometalate and graphene oxide as an electrocatalyst for the hydrogen evolution reaction

A new polyoxometalate (POM)-based hybrid nanomaterial (denoted as PMo11-Cr-mGO) was designed via covalent interaction between the Cr(acac)3 complex and [PMo11O39]7- followed by immobilization on the surface of modified graphene oxide (mGO). The prepared nanomaterial was characterized using a series of physicochemical techniques. X-ray diffraction (XRD), Raman analysis, transmission electron microscopy (TEM), and FE-SEM-EDS revealed the preservation of layered GO during the formation of the desired hybrid nanomaterial. Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), and elemental analysis confirmed the immobilization of POM (PMo11-Cr) on the surface of mGO and the formation of PMo11-Cr-mGO. In order to evaluate the performance of PMo11-Cr-mGO in the hydrogen evolution reaction (HER), electrochemical measurements were also performed. The resulting PMo11-Cr-mGO exhibited excellent HER activities with a low overpotential of 153 mV at 10 mA cm-2 and good durability in acidic media, thus emerging as one of the most efficient POM-based electrocatalysts.

Magnetic Field-Enhanced Electrocatalytic Oxygen Evolution on a Mixed-Valent Cobalt-Modulated LaCoO3 Catalyst

Extensive efforts to enhance the oxygen evolution reaction (OER) catalytic performance of transition metal oxides mainly concentrate on the extrinsic morphology tailoring, lattice doping, and electrode interface optimizing. Nevertheless, little room is left for performance improvement using these methods and an obvious gap still exists compared to the precious metal catalysts. In this work, a novel "mixed-valent cobalt modulation" strategy is presented to enhance the electrocatalytic OER of perovskite LaCoO₃ (LCO) oxide. The valence transition of cobalt is realized by ethylenediamine post reduction procedure at room temperature, which further induces the variation of magnetic properties for LCO catalyst. The optimized LCO catalyst with Co²⁺ /Co³⁺ of 1.98 % exhibits the best OER activity, and the overpotential at 10 mA cm^-2 current density is decreased by 170 mV compared pristine LCO. Impressively, the ferromagnetic LCO catalyst can perform magnetic OER enhancement. By application of an external magnetic field, the overpotential of LCO at 10 mA cm^-2 can be further decreased by 20 mV compared to that of under zero magnetic field, which arises from the enhanced energy states of electrons and accelerated electron transfer process driven by magnetic field. Our findings may provide a promising strategy to break the bottleneck for further enhancement of OER performance.

CoW Bimetallic Carbide Nanocatalysts: Computational Exploration, Confined Disassembly-Assembly Synthesis and Alkaline/Seawater Hydrogen Evolution

Earth-abundant tungsten carbide exhibits potential hydrogen evolution reaction (HER) catalytic activity owing to its Pt-like d-band electronic structure, which, unfortunately, suffers from the relatively strong tungsten-hydrogen binding, deteriorating its HER performance. Herein, a catalyst design concept of incorporating late transition metal into early transition metal carbide is proposed for regulating the metal-H bonding strength and largely enhancing the HER performance, which is employed to synthesize CoW bi-metallic carbide Co₆ W₆ C by a "disassembly-assembly" approach in a confined environment. Such synthesized Co₆ W₆ C nanocatalyst features the optimal Gibbs free energy of *H intermediate and dissociation barrier energy of H₂ O molecules as well by taking advantage of the electron complementary effect between Co and W species, which endows the electrocatalyst with excellent HER performance in both alkaline and seawater/alkaline electrolytes featuring especially low overpotentials, elevated current densities, and much-enhanced operation durability in comparison to commercial Pt/C catalyst. Moreover, a proof-of-concept Mg/seawater battery equipped with Co₆ W₆ C-2-600 as cathode offers a peak power density of 9.1 mW cm^-2 and an open-circuit voltage of ≈1.71 V, concurrently realizing hydrogen production and electricity output.

Light induced ammonia synthesis by crystalline polyoxometalate-based hybrid frameworks coupled with the Sv-1T MoS2 cocatalyst

A series of crystalline polyoxometalate-based hybrid frameworks coupled with rich sulfur vacancy 1T MoS2 through the hydrothermal growth strategy are presented towards light induced ammonia synthesis.

Defected MoS2 Modified by Vanadium-Substituted Keggin-Type Polyoxometalates as Electrocatalysts for Triiodide Reduction in Dye-Sensitized Solar Cells

The rational design of efficient triiodide reduction reaction catalysts that are dependent on cheap and ample elements on Earth has become a challenge. As an extremely encouraging non-noble metallic catalyst, MoS₂ requires effective strategies to improve the site accessibility, inherent conductivity, and structural stability. Here, vanadium-substituted Keggin-type polyoxometalates (POMs) can be used as electron aggregates to modify manganese (Mn)-doped MoS₂ through the electrochemical deposition strategy, thereby improving the charge transfer ability of MoS₂ to I^-/I₃^- redox pairs and accelerating the reduction of I₃^-. Additionally, with the increase in the number of vanadium atoms substituted in POMs, the conduction band of POMs and MoS₂ can also match better, which effectively reduces the energy loss and is more conducive to charge transfer. Meanwhile, the deposition of POMs can improve the stability of metastable MoS₂. When POMs/MoS₂ materials are used as the counter electrodes of dye-sensitized solar cells, the power conversion efficiency (PCE) obtained is 7.27%, which is higher than that of platinum (Pt) (6.07%). The PCE can still maintain the initial 96% after 9 days. This work provides a valuable way for the improvement of platinum-free catalysts with minimal expense, basic process, high efficiency, and good stability.