Interconnected Molybdenum Carbide-Based Nanoribbons for Highly Efficient and Ultrastable Hydrogen Evolution

Tuning the Catalytic Activity of MoS2-x-NbSx Heterostructure Nanosheets for Bifunctional Acidic Water Splitting

Developing durable electrocatalysts with high activity for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in acidic media is critically important for clean power production. In this study, MoS2-x-NbSx heterostructure nanosheets are synthesized from a solid-state reaction method followed by liquid phase exfoliation, and their catalytic performance is optimized. The MoS2-x-NbSx heterostructure nanosheets with optimal precursors ratio exhibit promising attributes for applications in the HER and OER compared to pristine MoS2 and Nb under the same conditions. The MoS2-x-NbSx heterostructure nanosheets catalyst on glassy carbon electrodes shows the minimum overpotential of 159 mV for HER and 295 mV for OER at a current density of 10 mA cm-2 in 0.5 m H2SO4. This research offers valuable insights into the fabrication of heterostructure nanosheets and evaluates their potential as effective electrocatalysts for water splitting compared with pristine 2D materials in an acid environment.

Ultrafine Mo2C nanoparticles embedded in an MOF derived N and P co-doped carbon matrix for an efficient electrocatalytic oxygen reduction reaction in zinc-air batteries

Exploring high-activity electrocatalysts for an oxygen reduction reaction (ORR) is of great significance for a variety of renewable energy conversion and storage technologies. Here, ultrafine Mo₂C nanoparticles assembled in N and P-co-doped carbon (Mo₂C@NPC) was developed from ZIF-8 encapsulated molybdenum-based polyoxometalates (PMo₁₂) as a highly efficient ORR electrocatalyst and shows excellent performance for zinc-air batteries. The well distribution of the PMo₁₂ in ZIF-8 results in the formation of ultrafine Mo₂C nanocrystallites encapsulated in a porous carbon matrix after pyrolysis. Significantly, from experimental and theoretical investigations, the highly porous structure, highly dispersed ultrafine Mo₂C and the N and P co-doping in the Mo₂C@NPC lead to the remarkable ORR activity with an onset potential of ∼1.01 V, a half-wave potential of ∼0.90 V and a Tafel slope of 51.7 mV dec^-1 at 1600 rpm in 0.1 M KOH. In addition, the Mo₂C@NPC as an ORR catalyst in zinc-air batteries achieved a high power density of 266 mW cm^-2 and a high specific capacity of 780.9 mA h g^-1, exceeding that driven by commercial Pt/C. Our results revealed that the porous architecture and ultrafine Mo₂C nanocrystallites of the electrocatalysts could facilitate mass transport and increase the accessibility of active sites, thus optimizing their performances in an ORR. The present study provides some guidelines for the design and synthesis of efficient nanostructured electrocatalysts.

All-pH-Tolerant In-Plane Heterostructures for Efficient Hydrogen Evolution Reaction

Generally, electrocatalytic hydrogen evolution reaction (HER) by water splitting is a pH-dependent reaction, which limits the widespread harvesting of hydrogen energy. Herein, we present a simple way for chemical bonding of MoS₂ (002) planes and α-MoC {111} planes to form in-plane heterostructures capable of efficient pH-universal HER. Due to the lattice strain from mismatched lattice parameters between α-MoC and MoS₂, this catalyst changes the electronic configuration of the MoS₂ and thus acquires the favorable proton adsorption and desorption activity, suggested by the platinum (Pt)-like free Gibbs energy. Consequently, only a low 78 mV overpotential is needed to achieve the current density of 10 mA cm^-2 in acidic solution along with a favorable Tafel kinetic process with a Tafel slope of 38.7 mV dec^-1. Owing to the synergistic interaction between MoS₂ (002) planes and α-MoC {111} planes with strong water dissociation activities, this catalyst also exhibits high HER performances beyond that of Pt in neutral and alkaline. This work proves the advances of in-plane heterostructures and illustrates the production of low-cost but highly efficient pH-universal HER catalytic materials, promising for future sustainable hydrogen energy.

MoS2 Nanoribbons with a Prolonged Photoresponse Lifetime for Enhanced Visible Light Photoelectrocatalytic Hydrogen Evolution

The high recombination rate of photoinduced electron-hole pairs limits the hydrogen production efficiency of the MoS₂ catalyst in photoelectrochemical (PEC) water splitting. The strategy of prolonging the lifetime of photoinduced carriers is of great significance to the promotion of photoelectrocatalytic hydrogen production. An ideal approach is to utilize edge defects, which can capture photoinduced electrons and thus slow down the recombination rate. However, for two-dimensional MoS₂, most of the surface areas are inert basal planes. Here, a simple method for preparing one-dimensional MoS₂ nanoribbons with abundant inherent edges is proposed. The MoS₂ nanoribbon-based device has a good spectral response in the range of 400-500 nm and has a longer lifetime of photoinduced carriers than other MoS₂ nanostructure-based photodetectors. An improved PEC catalytic performance of these MoS₂ nanoribbons is also experimentally verified under the illumination of 405 nm by using the electrochemical microcell technique. This work provides a new strategy to prolong the lifetime of photoinduced carriers for further improvement of PEC activity, and the evaluation of photoelectric performance provides a feasible way for transition-metal dichalcogenides to be widely used in the energy field.

Gas Bubbles in Electrochemical Gas Evolution Reactions

Electrochemical gas evolution reactions are of vital importance in numerous electrochemical processes including water splitting, chloralkaline process, and fuel cells. During gas evolution reactions, gas bubbles are vigorously and constantly forming and influencing these processes. In the past few decades, extensive studies have been performed to understand the evolution of gas bubbles, elucidate the mechanisms of how gas bubbles impact gas evolution reactions, and exploit new bubble-based strategies to improve the efficiency of gas evolution reactions. In this feature article, we summarize the classical theories as well as recent advancements in this field and provide an outlook on future research topics.

Big to Small: Ultrafine Mo2 C Particles Derived from Giant Polyoxomolybdate Clusters for Hydrogen Evolution Reaction

Due to its electronic structure, similar to platinum, molybdenum carbides (Mo₂ C) hold great promise as a cost-effective catalyst platform. However, the realization of high-performance Mo₂ C catalysts is still limited because controlling their particle size and catalytic activity is challenging with current synthesis methods. Here, the synthesis of ultrafine β-Mo₂ C nanoparticles with narrow size distribution (2.5 ± 0.7 nm) and high mass loading (up to 27.5 wt%) on graphene substrate using a giant Mo-based polyoxomolybdate cluster, Mo₁₃₂ ((NH₄ )₄₂ [Mo₁₃₂ O₃₇₂ (CH₃ COO)₃₀ (H₂ O)₇₂ ]·10CH₃ COONH₄ ·300H₂ O) is demonstrated. Moreover, a nitrogen-containing polymeric binder (polyethyleneimine) is used to create MoN bonds between Mo₂ C nanoparticles and nitrogen-doped graphene layers, which significantly enhance the catalytic activity of Mo₂ C for the hydrogen evolution reaction, as is revealed by X-ray photoelectron spectroscopy and density functional theory calculations. The optimal Mo₂ C catalyst shows a large exchange current density of 1.19 mA cm^-2 , a high turnover frequency of 0.70 s^-1 as well as excellent durability. The demonstrated new strategy opens up the possibility of developing practical platinum substitutes based on Mo₂ C for various catalytic applications.

Structural Design and Electronic Modulation of Transition-Metal-Carbide Electrocatalysts toward Efficient Hydrogen Evolution

As the key of hydrogen economy, electrocatalytic hydrogen evolution reactions (HERs) depend on the availability of cost-efficient electrocatalysts. Over the past years, there is a rapid rise in noble-metal-free electrocatalysts. Among them, transition metal carbides (TMCs) are highlighted due to their structural and electronic merits, e.g., high conductivity, metallic band states, tunable surface/bulk architectures, etc. Herein, representative efforts and progress made on TMCs are comprehensively reviewed, focusing on the noble-metal-like electronic configuration and the relevant structural/electronic modulation. Briefly, specific nanostructures and carbon-based hybrids are introduced to increase active-site abundance and to promote mass transportation, and heteroatom doping and heterointerface engineering are encouraged to optimize the chemical configurations of active sites toward intrinsically boosted HER kinetics. Finally, a perspective on the future development of TMC electrocatalysts is offered. The overall aim is to shed some light on the exploration of emerging materials in energy chemistry.

Scalable Synthesis of a Ruthenium-Based Electrocatalyst as a Promising Alternative to Pt for Hydrogen Evolution Reaction

Designing highly active, stable, and cost-efficient electrocatalysts as alternatives to replace Pt is extremely desirable for hydrogen evolution reaction (HER). Despite much progress that has been made based on complete nonprecious metals (NPMs), very few NPM catalysts have shown comparable performance to Pt-based catalysts. Herein, a cost-efficient, environmentally friendly, and scalable method to synthesize a novel ruthenium(Ru)-doped transition-metal carbide (Mo₂C) hybrid catalyst was proposed. The hybrid nanoparticles were uniformly distributed and strongly embedded in a biomass-derived highly porous N-doped carbon framework. In particular, Mo₂C@Ru exhibited a Pt-like remarkable electrocatalytic performance for HER, and it only required an extremely low overpotential of 24.6 mV to reach the current density of 10 mA cm^-2. Furthermore, our density functional theory calculations indicated that the nanocomposite exhibits improved metal-hydrogen binding and favorable hydrogen adsorption energy, which is comparable to that of Pt. The facile and scalable synthesis methodology, the relatively low cost, and the excellent electrochemical HER performance comparable to that of commercial Pt/C suggest that the Mo₂C@Ru electrocatalyst is a promising alternative to Pt for large-scale hydrogen production.

Mesoporous Mo2C/Carbon Hybrid Nanotubes Synthesized by a Dual-Template Self-Assembly Approach for an Efficient Hydrogen Production Electrocatalyst

Molybdenum carbide-containing nanomaterials have drawn considerable attention in the application of hydrogen production electrocatalysts in light of the high abundance, low cost, and Pt-like electronic structure of molybdenum carbide. In this article, we report the synthesis of one-dimensional (1D) Mo₂C/carbon mesoporous nanotubes (Mo₂C/C PNTs) through a dual-template self-assembly approach, which employs 1D MoO₃ nanobelts as the structure-directing template as well as one of the Mo₂C precursors, along with block copolymer (BCP) micelles as the pore-forming template. In aqueous solution, the interface self-assembly of the micelles with pyrrole (Py) molecules absorbed in the PEO domains leads to the tight arrangement of the micelles on the surfaces of the MoO₃ nanobelts. The polymerization of Py and the subsequent pyrolysis at 800 °C under a nitrogen atmosphere yield Mo₂C/C PNTs with well-defined mesopores. Among the resultant Mo₂C/C PNT samples, Mo₂C/C PNTs with a specific surface area of 69 m²/g, a N atom percentage of 5.5 atom %, and an optimum Mo₂C content of 40 wt % exhibit the highest HER catalytic performance in 0.5 M H₂SO₄ electrolyte, with a low onset potential of 34 mV, a satisfied overpotential of 140 mV at 10 mA/cm², and excellent cycling stability. This study not only opens an avenue toward new Mo₂C-containing nanomaterials but also provides a new system for the fundamental study on 1D porous nanohybrids with potential applications as hydrogen production electrocatalysts.

Molybdenum Carbide Nanoparticles Coated into the Graphene Wrapping N-Doped Porous Carbon Microspheres for Highly Efficient Electrocatalytic Hydrogen Evolution Both in Acidic and Alkaline Media

Molybdenum carbide (Mo2C) is recognized as an alternative electrocatalyst to noble metal for the hydrogen evolution reaction (HER). Herein, a facile, low cost, and scalable method is provided for the fabrication of Mo2C-based eletrocatalyst (Mo2C/G-NCS) by a spray-drying, and followed by annealing. As-prepared Mo2C/G-NCS electrocatalyst displays that ultrafine Mo2C nanopartilces are uniformly embedded into graphene wrapping N-doped porous carbon microspheres derived from chitosan. Such designed structure offer several favorable features for hydrogen evolution application: 1) the ultrasmall size of Mo2C affords a large exposed active sites; 2) graphene-wrapping ensures great electrical conductivity; 3) porous structure increases the electrolyte-electrode contact points and lowers the charge transfer resistance; 4) N-dopant interacts with H+ better than C atoms and favorably modifies the electronic structures of adjacent Mo and C atoms. As a result, the Mo2C/G-NCS demonstrates superior HER activity with a very low overpotential of 70 or 66 mV to achieve current density of 10 mA cm-2, small Tafel slope of 39 or 37 mV dec-1, respectively, in acidic and alkaline media, and high stability, indicating that it is a great potential candidate as HER electrocatalyst.