Carbon-encapsulated multi-phase nanocomposite of W2C@WC1-x as a highly active and stable electrocatalyst for hydrogen generation

Carbon encapsulated nanoparticles: materials science and energy applications

The technological implementation of electrochemical energy conversion and storage necessitates the acquisition of high-performance electrocatalysts and electrodes. Carbon encapsulated nanoparticles have emerged as an exciting option owing to their unique advantages that strike a high-level activity-stability balance. Ever-growing attention to this unique type of material is partly attributed to the straightforward rationale of carbonizing ubiquitous organic species under energetic conditions. In addition, on-demand precursors pave the way for not only introducing dopants and surface functional groups into the carbon shell but also generating diverse metal-based nanoparticle cores. By controlling the synthetic parameters, both the carbon shell and the metallic core are facilely engineered in terms of structure, composition, and dimensions. Apart from multiple easy-to-understand superiorities, such as improved agglomeration, corrosion, oxidation, and pulverization resistance and charge conduction, afforded by the carbon encapsulation, potential core-shell synergistic interactions lead to the fine-tuning of the electronic structures of both components. These features collectively contribute to the emerging energy applications of these nanostructures as novel electrocatalysts and electrodes. Thus, a systematic and comprehensive review is urgently needed to summarize recent advancements and stimulate further efforts in this rapidly evolving research field.

From atomic bonding to heterointerfaces: Co2P/WC constructed by lacunary polyoxometalates induced strategy as efficient hydrogen evolution electrocatalysts at all pH values

Herein, a novel in-situ "atomic binding to heterointerface" strategy is proposed to obtain Co₂P/WC@NC/CNTs catalyst with abundant heterointerface between cobalt phosphide and tungsten carbide (Co₂P/WC) by the polyoxometalates (POMs)-based metal-organic frameworks (MOFs) precursor. The natural quasi interfaces in K₁₀[Co₄(H₂O)₂(PW₉O₃₄)₂] molecule crucially guide the abundant Co₂P/WC heterointerfaces down to atomic level. Meanwhile, MOFs cages can effectively encapsulate nanosized POMs at molecular level to control the size and dispersion of Co₂P/WC nanoparticle, while carbon nanotubes (CNTs) enhance conductivity at nanoscale level. The interfacial electronic modulation between Co₂P and WC lowering the energy barrier of the rate determining step, thus Co₂P/WC@NC/CNTs showed reasonable hydrogen evolution reaction (HER) activity and stability in all-pH media including sea water. This work provides a "bottom-up" synthetic strategy for confined heterostructures, thus offering the prospect for more efficient interfacial charge modulation.

Synergistic Effects in Ultrafine Molybdenum-Tungsten Bimetallic Carbide Hollow Carbon Architecture Boost Hydrogen Evolution Catalysis and Lithium-Ion Storage

Constructing hierarchical heterostructures is considered a useful strategy to regulate surface electronic structure and improve the electrochemical kinetics. Herein, the authors develop a hollow architecture composed of MoC_{1- x} and WC_{1- x} carbide nanoparticles and carbon matrix for boosting electrocatalytic hydrogen evolution and lithium ions storage. The hybridization of ultrafine nanoparticles confined in the N-doped carbon nanosheets provides an appropriate hydrogen adsorption free energy and abundant boundary interfaces for lithium intercalation, leading to the synergistically enhanced composite conductivity. As a proof of concept, the as-prepared catalyst exhibits outstanding and durable electrocatalytic performance with a low overpotential of 103 and 163 mV at 10 mA cm^-2 , as well as a Tafel slope of 58 and 90 mV dec^-1 in alkaline electrolyte and acid electrolyte, respectively. Moreover, evaluated as an anode for a lithium-ion battery, the as-resulted sample delivers a rate capability of 1032.1 mA h g^-1 at 0.1 A g^-1 . This electrode indicates superior cyclability with a capability of 679.1 mA h g^-1 at 5 A g^-1 after 4000 cycles. The present work provides a strategy to design effective and stable bimetallic carbide composites as superior electrocatalysts and electrode materials.

Bifunctional WC-Supported RuO2 Nanoparticles for Robust Water Splitting in Acidic Media

We report the strong catalyst-support interaction in WC-supported RuO₂ nanoparticles (RuO₂ -WC NPs) anchored on carbon nanosheets with low loading of Ru (4.11 wt.%), which significantly promotes the oxygen evolution reaction activity with a η₁₀ of 347 mV and a mass activity of 1430 A g_Ru ^-1 , eight-fold higher than that of commercial RuO₂ (176 A g_Ru ^-1 ). Theoretical calculations demonstrate that the strong catalyst-support interaction between RuO₂ and the WC support could optimize the surrounding electronic structure of Ru sites to reduce the reaction barrier. Considering the likewise excellent catalytic ability for hydrogen production, an acidic overall water splitting (OWS) electrolyzer with a good stability constructed by bifunctional RuO₂ -WC NPs only requires a cell voltage of 1.66 V to afford 10 mA cm^-2 . The unique 0D/2D nanoarchitectures rationally combining a WC support with precious metal oxides provides a promising strategy to tradeoff the high catalytic activity and low cost for acidic OWS applications.

Catalyst overcoating engineering towards high-performance electrocatalysis

Clean and sustainable energy needs the development of advanced heterogeneous catalysts as they are of vital importance for electrochemical transformation reactions in renewable energy conversion and storage devices. Advances in nanoscience and material chemistry have afforded great opportunities for the design and optimization of nanostructured electrocatalysts with high efficiency and practical durability. In this review article, we specifically emphasize the synthetic methodologies for the versatile surface overcoating engineering reported to date for optimal electrocatalysts. We discuss the recent progress in the development of surface overcoating-derived electrocatalysts potentially applied in polymer electrolyte fuel cells and water electrolyzers by correlating catalyst intrinsic structures with electrocatalytic properties. Finally, we present the opportunities and perspectives of surface overcoating engineering for the design of advanced (electro)catalysts and their deep exploitation in a broad scope of applications.

Structure-controlled tungsten carbide nanoplates for enhanced hydrogen evolution reaction

Developing a low-cost and durable non-noble metal eletrocatalyst for hydrogen evolution reaction (HER) is critical in efficient hydrogen production. Herein, tungsten carbide nanoplates (WC NPs) with typical mesoporous structure were prepared by a controlled hydrothermal reaction followed by a gas-solid carburization process. The crystal phases, microstructure and chemical components of the nanoplates were characterized, and their electrochemical properties were measured. The results show that the as-prepared WC NPs expose active sites upmost, and exhibit enhanced conductivity and superior HER performance in acid solution in terms of a small η 10 (overpotential to obtain a current density of 10 mA cm−2) of 120 mV, a Tafel slope of 58 mV dec−1 and outstanding long-term cycling stability. These indicate that the HER properties of WC NPs are dramatically enhanced compared to that of all phase pure WC materials reported in recent years. This enhancement can be attributed to their unique structural and electronic properties, which can be exploited to improve the electrochemical properties of traditional non-noble metal material.

Solvent-Free Synthesis of Ultrafine Tungsten Carbide Nanoparticles-Decorated Carbon Nanosheets for Microwave Absorption

Carbides/carbon composites are emerging as a new kind of binary dielectric systems with good microwave absorption performance. Herein, we obtain a series of tungsten carbide/carbon composites through a simple solvent-free strategy, where the solid mixture of dicyandiamide (DCA) and ammonium metatungstate (AM) is employed as the precursor. Ultrafine cubic WC1-x nanoparticles (3-4 nm) are in situ generated and uniformly dispersed on carbon nanosheets. This configuration overcomes some disadvantages of conventional carbides/carbon composites and is greatly helpful for electromagnetic dissipation. It is found that the weight ratio of DCA to AM can regulate chemical composition of these composites, while less impact on the average size of WC1-x nanoparticles. With the increase in carbon nanosheets, the relative complex permittivity and dielectric loss ability are constantly enhanced through conductive loss and polarization relaxation. The different dielectric properties endow these composites with distinguishable attenuation ability and impedance matching. When DCA/AM weight ratio is 6.0, the optimized composite can produce good microwave absorption performance, whose strongest reflection loss intensity reaches up to - 55.6 dB at 17.5 GHz and qualified absorption bandwidth covers 3.6-18.0 GHz by manipulating the thickness from 1.0 to 5.0 mm. Such a performance is superior to many conventional carbides/carbon composites.

Designed synthesis of WC-based nanocomposites as low-cost, efficient and stable electrocatalysts for the hydrogen evolution reaction

In this study, effectively conductive rGO (reduced graphene oxide) was used as the supporter both to promote charge transfer and to refine particle size of WC, to realize efficient and stable HER performance.

Three-dimensional macroporous W2C inverse opal arrays for the efficient hydrogen evolution reaction

The development of a low-cost and durable non-precious metal-based electrocatalyst for the hydrogen evolution reaction (HER) is important to realize highly efficient overall water splitting. Here, we report the design and fabrication of a binder-free electrocatalyst of three-dimensional macroporous ditungsten carbide (W2C) inverse opal (W2C IO) arrays by a facile thermal carburization process with WO3 IO as a template. The as-fabricated W2C IO exhibits superior electrocatalytic performance in 0.5 M H2SO4 solution in terms of a low overpotential of 146 mV to reach a current density of 10 mA cm-2, a low Tafel slope of 78 mV dec-1 and excellent long-term stability. The superior performance can be attributed to the favorable electronic structure and hydrogen adsorption Gibbs free energy of W2C evidenced by theory calculations and the enhancement of the charge/mass transfer process by the 3D macroporous arrayed electrode design.

W2C nanodot-decorated CNT networks as a highly efficient and stable electrocatalyst for hydrogen evolution in acidic and alkaline media

Although tungsten carbide (W2C) has long been reported as an excellent platinum-like catalyst, it is still a challenge to synthesize W2C as an electrocatalyst for a highly efficient hydrogen evolution reaction (HER) due to its high onset overpotential, inevitable aggregation, and lack of a scalable and controllable synthesis method. Herein, we synthesized W2C nanodot-decorated CNT networks (W2C@CNT-S) via a facile and scalable spray drying method followed by a carbonization process. It is demonstrated that this unique nanoarchitecture, constructed by ultrafine W2C nanodots homogeneously decorated on a three-dimensional and conductive CNT skeleton, leads to the exposure of abundant catalytic sites and promotes highly efficient electron transfer and ion diffusion during the HER process. As a result, in acidic and alkaline media, the optimized W2C@CNT-S hybrid exhibited excellent HER performance with very low onset overpotentials of only 60 and 40 mV (vs. RHE) and very small Tafel slopes of 57.4 and 56.2 mV dec-1, and only needed 176 and 148 mV (vs. RHE) to obtain a current density of 10 mA cm-2, respectively; it also showed outstanding long-term durability even after a 30-hour test in both acidic and alkaline media. This study presents an overview of a low-cost and scalable spray-drying strategy to synthesize a high-performance carbide-based electrocatalyst for hydrogen evolution.