Twinned Tungsten Carbonitride Nanocrystals Boost Hydrogen Evolution Activity and Stability

Tungsten-Based Nanocatalysts: Research Progress and Future Prospects

The high price of noble metal resources limits its commercial application and stimulates the potential for developing new catalysts that can replace noble metal catalysts. Tungsten-based catalysts have become the most important substitutes for noble metal catalysts because of their rich resources, friendly environment, rich valence and better adsorption enthalpy. However, some challenges still hinder the development of tungsten-based catalysts, such as limited catalytic activity, instability, difficult recovery, and so on. At present, the focus of tungsten-based catalyst research is to develop a satisfactory material with high catalytic performance, excellent stability and green environmental protection, mainly including tungsten atomic catalysts, tungsten metal nanocatalysts, tungsten-based compound nanocatalysts, and so on. In this work, we first present the research status of these tungsten-based catalysts with different sizes, existing forms, and chemical compositions, and further provide a basis for future perspectives on tungsten-based catalysts.

Highly dispersed ruthenium nanoparticles on nitrogen doped carbon toward efficient hydrogen evolution in both alkaline and acidic electrolytes

Efficient and inexpensive electrocatalysts toward the hydrogen evolution reaction (HER) play an important role in electrochemical water splitting. Herein, we report the synthesis of highly dispersed ruthenium nanoparticles (2.2 ± 0.4 nm) on nitrogen doped carbon (Ru/N-C) by chemical reduction of RuCl₃ on carbon in the presence of polyvinylpyrrolidone in combination with subsequent pyrolysis. Ru/N-C exhibits an excellent overpotential of 13.5 and 18.5 mV at 10 mA cm⁻² in 1.0 M KOH and 0.5 M H₂SO₄ aqueous solution, respectively, much better than and comparable to those of commercial Pt/C (38.0 and 10.0 mV). The exceptional HER activity arises from high surface area of ultrafine Ru nanoparticles and appropriate Ru electronic state tuned by nitrogen dopant. Furthermore, Ru/N-C demonstrates excellent durability in both alkaline and acidic condition relative to commercial Pt/C. We speculate that the nitrogen dopant might have coordinated with Ru and tightly anchored Ru nanoparticles, preventing them from agglomerating.

Ultrafine ruthenium nanoparticles on nitrogen doped carbon show exceptional activity toward the hydrogen evolution reaction in alkaline and acidic electrolytes.

Modulating the Electronic Structure of Nickel Sulfide Electrocatalysts by Chlorine Doping toward Highly Efficient Alkaline Hydrogen Evolution

The exploration of indurative and stable low-cost catalysts for hydrogen evolution reaction (HER) is of great importance for hydrogen energy economy, but it still faces challenges. Herein, we report a Cl-doped Ni₃S₂ (Cl-Ni₃S₂) nanoplate catalyst vertically grown on Ni foam with outstanding activity and durability for HER, which only requires an overpotential of 67 mV to reach a current density of 10 mA cm^-2 in alkaline media and exhibits negligible degradation after 30 h of operation. Both the advanced X-ray absorption fine structure (XAFS) and density functional theory (DFT) calculation validate that Cl doping can optimize the electronic structure and the intrinsic activity of Ni₃S₂. This study devoted to the revelation of the impact of ionic doping on the activity of catalysts at the atomic scale can provide the direction for the rational design of novel and advanced HER electrocatalysts.

Shining Light on Anion-Mixed Nanocatalysts for Efficient Water Electrolysis: Fundamentals, Progress, and Perspectives

This review introduces recent advances of various anion-mixed transition metal compounds (e.g., nitrides, halides, phosphides, chalcogenides, (oxy)hydroxides, and borides) for efficient water electrolysis applications in detail. The challenges and future perspectives are proposed and analyzed for the anion-mixed water dissociation catalysts, including polyanion-mixed and metal-free catalyst, progressive synthesis strategies, advanced in situ characterizations, and atomic level structure-activity relationship. Hydrogen with high energy density and zero carbon emission is widely acknowledged as the most promising candidate toward world's carbon neutrality and future sustainable eco-society. Water-splitting is a constructive technology for unpolluted and high-purity H₂ production, and a series of non-precious electrocatalysts have been developed over the past decade. To further improve the catalytic activities, metal doping is always adopted to modulate the 3d-electronic configuration and electron-donating/accepting (e-DA) properties, while for anion doping, the electronegativity variations among different non-metal elements would also bring some potential in the modulations of e-DA and metal valence for tuning the performances. In this review, we summarize the recent developments of the many different anion-mixed transition metal compounds (e.g., nitrides, halides, phosphides, chalcogenides, oxyhydroxides, and borides/borates) for efficient water electrolysis applications. First, we have introduced the general information of water-splitting and the description of anion-mixed electrocatalysts and highlighted their complementary functions of mixed anions. Furthermore, some latest advances of anion-mixed compounds are also categorized for hydrogen and oxygen evolution electrocatalysis. The rationales behind their enhanced electrochemical performances are discussed. Last but not least, the challenges and future perspectives are briefly proposed for the anion-mixed water dissociation catalysts.

Construction of an N-Decorated Carbon-Encapsulated W2C/WP Heterostructure as an Efficient Electrocatalyst for Hydrogen Evolution in Both Alkaline and Acidic Media

Tungsten carbide (W₂C) has emerged as a potential alternative to noble-metal catalysts toward hydrogen evolution reaction (HER) owing to its Pt-like electronic configuration. However, unsatisfactory activity, dilatory electron transfer, and inefficient synthesizing methods, especially for nanoscale particles, have severely hindered its large-scale applications. Herein, a novel heterostructure composed of W₂C and tungsten phosphide (WP) embedded in nitrogen-decorated carbon (W₂C/WP@NC) was constructed as an efficient HER electrocatalyst. The as-prepared W₂C/WP@NC catalyst exhibits remarkable electrocatalytic activity and robust durability toward HER both in acids and bases. More notably, the W₂C/WP@NC catalyst demonstrates low overpotentials of 116.37 and 196.2 mV to afford a current density of 10 mA cm^-2 and reveals slight potential decays of about 6.4 and 7.64% over 12 h continuous operation in bases and acids, respectively. The overall water-splitting performance was further evaluated using the W₂C/WP@NC catalyst as the cathode and commercial RuO₂ as the anode in an electrolyzer, which can realize an overall current density of 10 mA cm^-2 and maintain long durability of more than 12 h with a small cell voltage of 1.723 V. This work opens up new opportunities for exploring cost-efficient electrocatalysts in sustainable energy conversion.

Designing Zn-doped nickel sulfide catalysts with an optimized electronic structure for enhanced hydrogen evolution reaction

Designing non-noble-metal electrocatalysts with excellent performance and economic benefits toward the hydrogen evolution reaction (HER) is extremely crucial for future energy development. In particular, the rational cationic-doped strategy can effectively tailor the electronic structure of the catalysts and improve the free energy of the adsorbed intermediate, thus enhancing HER performance. Herein we reported Zn-doped Ni₃S₂ nanosheet arrays supported on Ni foam (Zn-Ni₃S₂/NF) that were synthesized by a two-step hydrothermal process for improving HER catalysis under alkaline conditions. Remarkably, the obtained Zn-Ni₃S₂/NF displays excellent HER catalytic performance with an overpotential of 78 mV to reach a current density of 10 mA cm^-2 and dramatic long-term stability for 18 h in 1 M KOH. In addition, the results based on the density functional theory calculations reveal that Zn dopants can modulate the electronic structure of Ni₃S₂ and optimize the hydrogen adsorption free energy (ΔG_H*). Thus cationic-doping engineering provides an efficient method to enhance the intrinsic activities of transition-metal sulfides, which may contribute to the development of nonprecious electrocatalysts for HER.

W2N/WC composite nanofibers as an efficient electrocatalyst for photoelectrochemical hydrogen evolution

A tungsten-based electrocatalyst for hydrogen evolution reaction is vital for developing sustainable and clean energy sources. Herein, W₂N/WC composite nanofibers were synthesized through electrospinning technology and simultaneous carbonization and N-doping at high temperature. The composite nanofiber has higher catalytic activity than any simple compound. It exhibits remarkable hydrogen evolution performance in acidic media with a low overpotential of -495 mV, at a current density of -50 mA cm^-2. The excellent hydrogen evolution performance of the composite nanofiber could be attributed to the abundant active sites, strong light absorption and fast charge transfer. The method used in this work provides a new possibility for the fabrication of high-performance electrocatalysts rationally.

Insight into electrocatalytic activity and mechanism of bimetal niobium-based oxides in situ embedded into biomass-derived porous carbon skeleton nanohybrids for photovoltaics and alkaline hydrogen evolution

Developing highly-efficient multifunctional electrocatalysts for energy conversion devices is of great importance. A sequence of nano-sized bimetal (Al, Cr, Fe) niobium oxide nanoparticles anchored on aloe peel-derived porous carbon skeleton hybrids (AN/APPC, CN/APPC, and FN/APPC) are successfully prepared via co-precipitation avenue and used as electrocatalysts for photovoltaics and alkaline hydrogen evolution reaction. Benefiting from the synergies between nano-sized metal niobium oxides and highly conductive porous carbon skeleton, these robust polycomponent hybrid electrocatalysts exhibit superior catalytic performances for accelerating the triiodide reduction and hydrogen evolution reaction. The solar cell with AN/APPC electrocatalyst achieves an outstanding device efficiency of 7.31%, superior to that with Pt (6.84%), and the AN/APPC electrocatalyst exhibit an overpotential (131.6 mV) when the current density is 10 mA cm^-2 and Tafel slope (54 mV dec^-1) in 1 M KOH for hydrogen evolution reaction. The AN/APPC electrocatalysts illustrate remarkable electrochemical durability in both I₃^-/I^- electrolyte and alkaline media. Furthermore, the catalytic mechanism was clarified both from the electronic structure and work function through first-principle density functional theory (DFT) calculations. This work opens a new avenue for electrocatalysis field via using nano-sized porous bio-carbon skeleton loaded with niobium-based binary metal.

Manipulating Interfaces of Electrocatalysts Down to Atomic Scales: Fundamentals, Strategies, and Electrocatalytic Applications

Raising electrocatalysis by rationally devising catalysts plays a core role in almost all renewable energy conversion and storage systems. The principal catalytic properties can be controlled and improved well by manipulation of interfaces, ascribed to the interactions among different components/players at the interfaces. In particular, manipulating interfaces down to atomic scales is becoming increasingly attractive, not only because those atoms at around the interface are the key players during electrocatalysis, but also, understandings on the atomic level electrocatalysis allow one to gain deep insights into the reaction mechanism. With the feature down-sizing to atomic scales, there is a timely need to redefine the interfaces, as some of them have gone beyond the conventionally perceived interfacial concept. In this overview, the key active players participating in the interfacial manipulation of electrocatalysts are examined, from a new angle of "atomic interface," including those individual atoms, defects, and their interactions, together with the essential characterization techniques for them. The specific approaches and pathways to engineer better atomic interfaces are investigated, and thus to enable the unique electrocatalysis for targeted applications. Looking beyond recent progress, the challenges and prospects of the atomic level interfacial engineering are also briefly visited.

Plasmonic Enhanced Reactive Oxygen Species Activation on Low-Work-Function Tungsten Nitride for Direct Near-Infrared Driven Photocatalysis

Realizing near-infrared (NIR) driven photocatalytic reaction is one of the promising strategies to promote the solar energy utilization and photocatalytic efficiencies. However, effective reactive oxygen species (ROS) activation under NIR irradiation remains to be great challenge for nearly all previously reported photocatalysts. Herein, the cubic-phase tungsten nitride (WN) with strong plasmonic NIR absorption and low-work function (≈3.59 eV) is proved to be able to mediate direct ROS activation by both of experimental observation and theoretical simulation. The cubic WN nanocubes (NCs) are synthesized via the hydrothermal-ammonia nitridation process and its NIR-driven photocatalytic properties, including photocatalytic degradation, hydroxylation, and de-esterification, are reported for the first time in this work. The 3D finite element simulation results demonstrate the size dependent and wavelength tuned plasmonic NIR absorption of the WN NCs. The NIR-driven photocatalytic mechanism of WN NCs is proposed based on density functional theory (DFT) calculated electronic structure and facet dependent O₂ (or H₂ O) molecular activation, radicals scavenging test, spin trapped electron paramagnetic resonance measurements, and ultraviolet photoelectronic spectrum (UPS). Overall, the results in this work pave a way for the application of low-work-function materials as highly reactive NIR photocatalyst.

RuO2 photodeposited on W-doped and Cr-doped TiO2 nanotubes with enhanced photoelectrochemical water splitting and capacitor properties

Two series of highly ordered Cr-doped TiO₂ (CT) and W-doped TiO₂ (WT) nanotubes were prepared by in situ anodizing and modified by photodeposition of RuO₂ for water splitting study.

Metal-organic Framework-driven Porous Cobalt Disulfide Nanoparticles Fabricated by Gaseous Sulfurization as Bifunctional Electrocatalysts for Overall Water Splitting

Both high activity and mass production potential are important for bifunctional electrocatalysts for overall water splitting. Catalytic activity enhancement was demonstrated through the formation of CoS2 nanoparticles with mono-phase and extremely porous structures. To fabricate porous structures at the nanometer scale, Co-based metal-organic frameworks (MOFs), namely a cobalt Prussian blue analogue (Co-PBA, Co3[Co(CN)6]2), was used as a porous template for the CoS2. Then, controlled sulfurization annealing converted the Co-PBA to mono-phase CoS2 nanoparticles with ~ 4 nm pores, resulting in a large surface area of 915.6 m2 g-1. The electrocatalysts had high activity for overall water splitting, and the overpotentials of the oxygen evolution reaction and hydrogen evolution reaction under the operating conditions were 298 mV and -196 mV, respectively, at 10 mA cm-2.

Synergism of Interface and Electronic Effects: Bifunctional N-Doped Ni3 S2 /N-Doped MoS2 Hetero-Nanowires for Efficient Electrocatalytic Overall Water Splitting

The realization of water electrolysis on the basis of highly active, cost-effective electrocatalysts is significant yet challenging for achieving sustainable hydrogen production from water. Herein, N-doped Ni₃ S₂ /N-doped MoS₂ 1D hetero-nanowires supported by Ni foam (N-Ni₃ S₂ /N-MoS₂ /NF) are readily synthesized through a chemical transformation strategy by using NiMoO₄ nanowire array growth on Ni foam (NiMoO₄ /NF) as the starting material. With the in situ generation of Ni₃ S₂ /MoS₂ heterointerfaces within nanowires and the incorporation of N^- anions, an extraordinary hydrophilic nature with abundant, well-exposed active sites and optimal reaction dynamics for both oxidation and reduction of water are obtained. Attributed to these properties, as-converted N-Ni₃ S₂ /N-MoS₂ /NF exhibits highly efficient electrocatalytic activities for both hydrogen and oxygen evolution reactions under alkaline conditions. The superior bifunctional properties of N-Ni₃ S₂ /N-MoS₂ /NF enable it to effectively catalyze the overall water-splitting reaction.

Tungsten-inert gas welding electrodes as low-cost, green and pH-universal electrocatalysts for the hydrogen evolution reaction

Lanthanated tungsten electrodes were shown to be green, durable, low-cost, pH-universal and efficient electrocatalysts for the hydrogen evolution reaction.