Sprout-like Growth of Mesoporous Mo2 C/NC Nanonetworks as Efficient Electrocatalysts for Hydrogen Evolution

Recent Advancements in Two-Dimensional Layered Molybdenum and Tungsten Carbide-Based Materials for Efficient Hydrogen Evolution Reactions

Green and renewable energy is the key to overcoming energy-related challenges such as fossil-fuel depletion and the worsening of environmental habituation. Among the different clean energy sources, hydrogen is considered the most impactful energy carrier and is touted as an alternate fuel for clean energy needs. Even though noble metal catalysts such as Pt, Pd, and Au exhibit excellent hydrogen evolution reaction (HER) activity in acid media, their earth abundance and capital costs are highly debatable. Hence, developing cost-effective, earth-abundant, and conductive electrocatalysts is crucial. In particular, various two-dimensional (2D) transition metal carbides and their compounds are gradually emerging as potential alternatives to noble metal-based catalysts. Owing to their improved hydrophilicity, good conductivity, and large surface areas, these 2D materials show superior stability and excellent catalytic performances during the HER process. This review article is a compilation of the different synthetic protocols, their impact, effects of doping on molybdenum and tungsten carbides and their derivatives, and their application in the HER process. The paper is more focused on the detailed strategies for improving the HER activity, highlights the limits of molybdenum and tungsten carbide-based electrocatalysts in electro-catalytic process, and elaborates on the future advancements expected in this field.

Highly Active Mo2C@WS2 Hybrid Electrode for Enhanced Hydrogen Evolution Reaction

Transition metal dichalcogenides (TMDs) are the auspicious inexpensive electrocatalysts for the hydrogen evolution reaction (HER) which has been broadly studied owing to their remarkable enactment, however the drought of factors understanding were highly influenced to hinder their electrocatalytic behavior. Recently, transition metal carbide (TMC) has also emerged as an attractive electrode material due to their excellent ionic and electronic transport behavior. In this work, Mo2C@WS2 hybrids have been fabricated through a simple chemical reaction method. Constructed heterostructure electrocatalyts presented the small Tafel slope of 59 and 95 mV per decade and low overpotential of 93 mV and 98 @10 mA·cm−2 for HER in acidic and alkaline solution, respectively. In addition, 24-h robust stability with the improved interfacial interaction demonstrated the suitability of hybrid electrocatalyst for HER than their pure form of Mo2C and WS2 structures. The derived outcomes describe the generated abundant active sites and conductivity enhancement in TMC/TMD heterostructure along with the weaken ion/electron diffusion resistance for efficient energy generation applications.

Self-supported nickel-doped molybdenum carbide nanoflower clusters on carbon fiber paper for an efficient hydrogen evolution reaction

Developing an efficient, stable and low-cost noble-metal-free electrocatalyst for the hydrogen evolution reaction (HER) is an effective way to alleviate the energy crisis. Herein, we report a simple and facile approach to synthesize self-supported Ni-doped Mo₂C via a molten salt method. By optimizing the content of Ni, the concentration of Ni(NO₃)₂, and the annealing time, self-supported nanoflower-like electrocatalysts composed of ultrathin nanosheets on carbon fiber paper (CFP) can be achieved. Such a fluffy and porous nanoflower-like structure has a large specific surface area, which can expose many active sites, and promote charge transfer; moreover, all of the above is beneficial for improving the HER performance. Density functional theory (DFT) calculations reveal that the doping of Ni leads to a down shift of the value of the d band center (ε_d), so that the adsorbed hydrogen (H_ads) is easier to desorb from the catalyst surface, thus leading to an enhanced intrinsic catalytic activity of Ni doped Mo₂C based catalysts. As a result, Mo₂C-3 M Ni(NO₃)₂/CFP with a nanoflower-like structure prepared at 1000 °C for 6 h exhibits the best electrocatalytic performance for the HER in 0.5 M H₂SO₄, with a low overpotential of 56 mV (at j = 10 mA cm^-2) and a Tafel slope (27.4 mV dec^-1) comparable to that of commercial Pt/C (25.8 mV dec^-1). The excellent performance surpasses most of the noble-metal-free electrocatalysts. In addition, the outstanding long-term durability of Mo₂C-3 M Ni(NO₃)₂/CFP is demonstrated by showing no obvious fluctuations during 35 h of the HER testing. This work provides a simple and facile strategy for the preparation of nanoelectrocatalysts with high specific surface areas and high catalytic activities, both of which promote an efficient HER.

Self-Supported Vanadium Carbide by an Electropolymerization-Assisted Method for Efficient Hydrogen Production

Exploring efficient electrodes toward the hydrogen evolution reaction (HER) remains a great challenge for large-scale hydrogen production. Owing to its high earth abundance, low electrical resistivity, and small density, vanadium carbide (VC) is a promising HER electrode candidate but has been rarely explored. In this work, VC nanoparticles encased in nitrogen-doped carbon matrix on carbon cloth (VC@NC/CC) were prepared as a binder-free HER cathode through electropolymerization followed by carbothermal reduction under argon. In the first step of pyrrole electropolymerization, the VO₄ ^3- anions, serving as both vanadium source and supporting electrolyte, were homogeneously incorporated in the positively charged polypyrrole (PPy) framework through coulombic interaction. The electropolymerization was effective for preparation of binder-free metal carbide materials with various polymer monomers as carbon source, which was favorable for the high performance of metal carbide electrodes. During the pyrolysis process, the polymeric hybrids were converted to VC nanoparticles and entrapped in the PPy-derived N-doped carbon matrix. The optimized VC@NC/CC electrode exhibited high catalytic activity and durability in both acidic and alkaline media. The use of VC for efficient HER is remarkable, and such a convenient and versatile electropolymerization-assisted method is appealing for the fabrication of industrially scalable large-area VC electrodes for efficient hydrogen production.

Bimetallic Au–Pd alloy nanoparticles supported on MIL-101(Cr) as highly efficient catalysts for selective hydrogenation of 1,3-butadiene

Gold–palladium (Au–Pd) bimetallic nanoparticle (NP) catalysts supported on MIL-101(Cr) with Au : Pd mole ratios ranging from 1 : 3 to 3 : 1 were prepared through coimpregnation and H₂ reduction. Au–Pd NPs were homogeneously distributed on the MIL-101(Cr) with mean particle sizes of 5.6 nm. EDS and XPS analyses showed that bimetallic Au–Pd alloys were formed in the Au(2)Pd(1)/MIL-101(Cr). The catalytic performance of the catalysts was explored in the selective 1,3-butadiene hydrogenation at 30–80 °C on a continuous fixed bed flow quartz reactor. The bimetallic Au–Pd alloy particles stabilized by MIL-101(Cr) presented improved catalytic performance. The as-synthesized bimetallic Au(2)Pd(1)/MIL-101(Cr) with 2 : 1 Au : Pd mole ratio showed the best balance between the activity and butene selectivity in the selective 1,3-butadiene hydrogenation. The Au–Pd bimetallic-supported catalysts can be reused in at least three runs. The work affords a reference on the utilization of a MOF and alloy nanoparticles to develop high-efficiency catalysts.

Bimetallic Au–Pd alloy particles stabilized by MIL-101(Cr) showed high activity and butene selectivity for 1,3-butadiene hydrogenation reaction.

Synthesis of Mo2C and W2C Nanoparticle Electrocatalysts for the Efficient Hydrogen Evolution Reaction in Alkali and Acid Electrolytes

The synthesis of low cost, high efficacy, and durable hydrogen evolution electrocatalysts from the non-noble metal group is a major challenge. Herein, we establish a simple and inexpensive chemical reduction method for producing molybdenum carbide (Mo2C) and tungsten carbide (W2C) nanoparticles that are efficient electrocatalysts in alkali and acid electrolytes for hydrogen evolution reactions (HER). Mo2C exhibits outstanding electrocatalytic behavior with an overpotential of -134 mV in acid medium and of -116 mV in alkaline medium, while W2C nanoparticles require an overpotential of -173 mV in acidic medium and -130 mV in alkaline medium to attain a current density of 10 mA cm-2. The observed results prove the capability of high- and low-pH active electrocatalysts of Mo2C and W2C nanoparticles to be efficient systems for hydrogen production through HER water electrolysis.

Facile preparation of molybdenum carbide (Mo2C) nanoparticles and its effective utilization in electrochemical sensing of folic acid via imprinting

Herein, we propose a facile chemical reduction method to synthesize the molybdenum carbide (Mo₂C) nanoparticles and its application for the electrochemical detection of folic acid (FA) through imprinting technique. Raman scattering, photoelectron spectroscopy and electron microscopy techniques were employed to study the properties of Mo₂C nanoparticles. FA imprinting was carried out in the presence of pyrrole monomer over Mo₂C modified glassy carbon electrode (GCE). The proposed sensor showed the detection behavior for wide range of FA concentrations from 0.01 μM to 120 μM with an excellent LOD value of 4 nM and good selectivity toward FA as compared to other co-existing species in real samples. The fabricated MIP-Mo₂C/GCE sensors were able to be replicated with ∼1.9% RSD, and their reproduced sensor offered good repeatability (RSD; 1.6%) and stability.

Janus CoN/Co cocatalyst in porous N-doped carbon: toward enhanced catalytic activity for hydrogen evolution

Using earth abundant transition metal-based compounds to replace noble metal catalysts towards hydrogen evolution from water splitting seems to have great importance worldwide.