Molybdenum Carbide‐Embedded Multichannel Hollow Carbon Nanofibers as Bifunctional Catalysts for Water Splitting

With the environmental pollution and non‐renewable fossil fuels, it is imperative to develop eco‐friendly, renewable, and highly efficient electrocatalysts for sustainable energy. Herein, a simple electrospinning process used to synthesis Mo₂C‐embedded multichannel hollow carbon nanofibers (Mo₂C‐MCNFs) and followed by the pyrolysis process. As prepared lotus root‐like nanoarchitecture could offer rich porosity and facilitate the electrolyte infiltration, the Mo₂C‐MCNFs delivered favourable catalytic activity for HER and OER. The resultant catalysts exhibit low overpotentials of 114 mV and 320 mV at a current density of 10 mA cm^?2 for HER and OER, respectively. Furthermore, using the Mo₂C‐MCNFs catalysts as a bifunctional electrode toward overall water splitting, which only needs a small cell voltage of 1.68 V to afford a current density of 10 mA cm^?2 in the home‐made alkaline electrolyzer. This interesting work presents a simple and effective strategy to further fabricating tunable nanostructures for energy‐related applications.     

An Efficient RuTe2/Graphene Catalyst for Electrochemical Hydrogen Evolution Reaction in Acid Electrolyte

Developing efficient powder catalysts for hydrogen evolution reaction (HER) in the acidic electrolyte is significant for hydrogen generation in the proton exchange membrane (PEM) water electrolysis technique. Herein, we demonstrated an efficient catalyst for HER in the acid media based on the graphene supported ruthenium telluride nanoparticles (RuTe₂/Gr). The catalysts were easily fabricated by a facile microwave irradiation/thermal annealing approach, and orthorhombic RuTe₂ crystals were found anchored over the graphene surface. The defective structure was demonstrated in the aberration‐corrected transmission electron microscopy images for RuTe₂ crystals and graphene support. This catalyst required an overpotential of 72 mV to drive 10 mA cm^?2 for HER when loading on the inert glass carbon electrode; Excellent catalytic stability in acidic media was also observed to offer 10 mA cm^?2 for 10 hours. The Volmer‐Tafel mechanism was indicated on RuTe₂/Gr catalyst by Tafel slope of 33 mV dec^?1, similar to that of Pt/C catalysts. The high catalytic performance of RuTe₂/Gr could be attributed to its high dispersion on the graphene surface, high electrical conductivity and low charge transfer resistance. This powder catalyst has potential application in the PEM water electrolysis technique because of its low cost and high stability.     

Molybdenum Carbide‐Oxide Heterostructures: In Situ Surface Reconfiguration toward Efficient Electrocatalytic Hydrogen Evolution

Heterostructured Mo₂C‐MoO_x on carbon cloth (Mo₂C‐MoO_x/CC), as a model of easily oxidized electrocatalysts under ambient conditions, is investigated to uncover surface reconfiguration during the hydrogen evolution reaction (HER). Raman spectroscopy combined with electrochemical tests demonstrates that the Mo^VI oxides on the surface are in situ reduced to Mo^IV, accomplishing promoted HER in acidic condition. As indicated by density functional theoretical calculations, the in situ reduced surface with terminal Mo=O moieties can effectively bring the negative ΔG_H* on bare Mo₂C close to a thermodynamic neutral value, addressing difficult H* desorption toward fast HER kinetics. The optimized Mo₂C‐MoO_x/CC only requires a low overpotential (η₁₀) of 60 mV at ?10 mA cm^?2 in 1.0 m HClO₄, outperforming Mo₂C/CC and most non‐precious electrocatalysts. In situ surface reconfiguration are shown on W₂C‐WO_x, highlighting the significance to boost various metal‐carbides and to identify active sites.     

Molybdenum Carbide-Oxide Heterostructures: In Situ Surface Reconfiguration toward Efficient Electrocatalytic Hydrogen Evolution

Heterostructured Mo₂C-MoO_x on carbon cloth (Mo₂C-MoO_x/CC), as a model of easily oxidized electrocatalysts under ambient conditions, is investigated to uncover surface reconfiguration during the hydrogen evolution reaction (HER). Raman spectroscopy combined with electrochemical tests demonstrates that the Mo^VI oxides on the surface are in situ reduced to Mo^IV, accomplishing promoted HER in acidic condition. As indicated by density functional theoretical calculations, the in situ reduced surface with terminal Mo=O moieties can effectively bring the negative ΔG_H* on bare Mo₂C close to a thermodynamic neutral value, addressing difficult H* desorption toward fast HER kinetics. The optimized Mo₂C-MoO_x/CC only requires a low overpotential (η₁₀) of 60 mV at −10 mA cm⁻² in 1.0 m HClO₄, outperforming Mo₂C/CC and most non-precious electrocatalysts. In situ surface reconfiguration are shown on W₂C-WO_x, highlighting the significance to boost various metal-carbides and to identify active sites.     

Porous Molybdenum Carbide Nanostructures Synthesized on Carbon Cloth by CVD for Efficient Hydrogen Production

Molybdenum carbide (Mo₂C) is a promising noble-metal-free electrocatalyst for the hydrogen evolution reaction (HER), due to its structural and electronic merits, such as high conductivity, metallic band states and wide pH applicability. Here, a simple CVD process was developed for synthesis of a Mo₂C on carbon cloth (Mo₂C@CC) electrode with carbon cloth as carbon source and MoO₃ as the Mo precursor. XRD, Raman, XPS and SEM results of Mo₂C@CC with different amounts of MoO₃ and growth temperatures suggested a two-step synthetic mechanism, and porous Mo₂C nanostructures were obtained on carbon cloth with 50 mg MoO₃ at 850 °C (Mo₂C-850(50)). With the merits of unique porous nanostructures, a low overpotential of 72 mV at current density of 10 mA cm⁻² and a small Tafel slope of 52.8 mV dec⁻¹ was achieved for Mo₂C-850(50) in 1.0 m KOH. The dual role of carbon cloth as electrode and carbon source resulted into intimate adhesion of Mo₂C on carbon cloth, offering fast electron transfer at the interface. Cyclic voltammetry measurements for 5000 cycles revealed that Mo₂C@CC had excellent electrochemical stability. This work provides a novel strategy for synthesizing Mo₂C and other efficient carbide electrocatalysts for HER and other applications, such as supercapacitors and lithium-ion batteries.     

Interfacial coupling of sea urchin-like (Mo4O11-MoS2-VO2) promoted electron redistributions for significantly boosted hydrogen evolution reaction

Developing efficient electrocatalysts for hydrogen evolution reaction (HER) is of great importance in contemporary water electrolysis technology. Here, a novel hierarchically sea urchin-like electrocatalyst (Mo₄O₁₁-MoS₂-VO₂) is synthesized by hydrothermal deposition and post-annealing strategy. The optimized electrocatalyst behaves as a high active hydrogen evolution electrode in 0.5 mol/L H₂SO₄. This electrode needs overpotential of only 43 mV to achieve 10 mA/cm² with a Tafel slope of 37 mV/dec and maintains its catalytic activity for at least 36 h. Better than most previously reported non-noble metal electrocatalysts anchored on carbon cloth. It is worth mentioning that the hierarchical sea urchin-like structure promotes the redistribution of electrons and provides more catalytic active sites. This strategy shows a way for the construction of inexpensive non-noble metal electrocatalysts in the future.     

Enhancement of hydrogen evolution activities of low-cost transition metal electrocatalysts in near-neutral strongly buffered aerobic media

The advantages of hydrogen evolution reaction (HER) in strongly buffered neutral pH are manifold including enhanced stability of the electrocatalysts, oxygen tolerance, safer and environmental friendly devices, etc., yet, not much research effort has been devoted on the subject. HER activities of several low-cost electrocatalysts like Mo₂C, MoS₂, CoSe₂ and NiSe₂ have been studied in sodium phosphate buffer solution of pH 5. An optimal buffer concentration of 1.75 M was observed for the electrocatalysts. Compared to un-buffered electrolyte, a reduction of about 100 mV in the onset overpotential has been achieved. The electrocatalysts are highly oxygen tolerant with more than 90% HER selectivities. Furthermore, electrochemical surface area of Mo₂C was evaluated by capacitance and surface oxidation methods to obtain an insight on the specific adsorption of buffer electrolytes.     

Hierarchical β‐Mo2C Nanotubes Organized by Ultrathin Nanosheets as a Highly Efficient Electrocatalyst for Hydrogen Production

Production of hydrogen by electrochemical water splitting has been hindered by the high cost of precious metal catalysts, such as Pt, for the hydrogen evolution reaction (HER). In this work, novel hierarchical β‐Mo₂C nanotubes constructed from porous nanosheets have been fabricated and investigated as a high‐performance and low‐cost electrocatalyst for HER. An unusual template‐engaged strategy has been utilized to controllably synthesize Mo‐polydopamine nanotubes, which are further converted into hierarchical β‐Mo₂C nanotubes by direct carburization at high temperature. Benefitting from several structural advantages including ultrafine primary nanocrystallites, large exposed surface, fast charge transfer, and unique tubular structure, the as‐prepared hierarchical β‐Mo₂C nanotubes exhibit excellent electrocatalytic performance for HER with small overpotential in both acidic and basic conditions, as well as remarkable stability.     

An insight to catalytic synergic effect of Pd-MoS2 nanorods for highly efficient hydrogen evolution reaction

The electrocatalytic hydrogen evolution reaction (HER) is a sustainable energy production route using green chemistry. Transition metal dichalcogenides' application in catalytic hydrogen production is limited due to a lack of solutions that simultaneously address intrinsic activity, increased surface area, electrical conductivity, and stability problems. Herein we address these issues simultaneously by modifying the electronic structure of molybdenum disulfide (MoS₂) nanorods using a low content of Pd (1 wt% and 2 wt%) dopant via a facile colloidal solvothermal route. The resulting MoS₂ nanorods doped with (1 and 2 wt%) palladium demonstrate current density of 100 mA/cm² at quit lower over-potentials of 137 mV and 119 mV than 273 mV for pure MoS₂ nanorods, accompanied by high stability. This research proposes a strategy for designing high-performance HER electrocatalysts that work in acidic medium. In addition, the Tafel slop calculated for MoS₂ is 112 mV/dec whereas for 1 and 2 wt% Pd-MoS₂, the Tafel slopes are 70 mV/dec and 46 mV/dec.     

Boron‐Dependency of Molybdenum Boride Electrocatalysts for the Hydrogen Evolution Reaction

Molybdenum‐based materials have been considered as alternative catalysts to noble metals, such as platinum, for the hydrogen evolution reaction (HER). We have synthesized four binary bulk molybdenum borides Mo₂B, α‐MoB, β‐MoB, and MoB₂ by arc‐melting. All four phases were tested for their electrocatalytic activity (linear sweep voltammetry) and stability (cyclic voltammetry) with respect to the HER in acidic conditions. Three of these phases were studied for their HER activity and by X‐ray photoelectron spectroscopy (XPS) for the first time; MoB₂ and β‐MoB show excellent activity in the same range as the recently reported α‐MoB and β‐Mo₂C phases, while the molybdenum richest phase Mo₂B show significantly lower HER activity, indicating a strong boron‐dependency of these borides for the HER. In addition, MoB₂ and β‐MoB show long‐term cycle stability in acidic solution.     

Optimization of the Hydrogen-Adsorption Free Energy of Ru-Based Catalysts towards High-Efficiency Hydrogen Evolution Reaction at all pH

The utilization of noble-metal catalysts for the hydrogen evolution reaction (HER) provides an efficient strategy for hydrogen acquisition. However, exploring catalysts with suitable hydrogen binding strength for the HER process is always of great importance, but extremely challenging. In this work, sulfur and phosphor as electron-withdrawing elements were incorporated into carbon nanotube (CNT)-supported Ru catalysts, which were prepared through a facile solution reduction reaction and post thermo treatment. Owing to the suitable electronegativity provided by P and synergistic effects of the carbon nanotubes, the RuP₂/CNT achieved a high catalytic performance as a HER electrocatalyst. This may result from the modulation effect of the electronic properties and the depressed adsorption free energy of RuP₂. Electrochemical tests present that the RuP₂/CNT composite exhibit a small overpotential of 58 mV at 10 mA cm⁻² in acidic electrolyte. In a neutral or alkaline environment, the overpotential is 82 and 40 mV, respectively. The RuP₂/CNT electrode also possesses stable durability for long-time cycling, suggesting its remarkable property as promising all-pH HER catalyst.     

Nanoporous Graphene with Single‐Atom Nickel Dopants: An Efficient and Stable Catalyst for Electrochemical Hydrogen Production

Single‐atom nickel dopants anchored to three‐dimensional nanoporous graphene can be used as catalysts of the hydrogen evolution reaction (HER) in acidic solutions. In contrast to conventional nickel‐based catalysts and graphene, this material shows superior HER catalysis with a low overpotential of approximately 50 mV and a Tafel slope of 45 mV dec^?1 in 0.5 M H₂SO₄ solution, together with excellent cycling stability. Experimental and theoretical investigations suggest that the unusual catalytic performance of this catalyst is due to sp–d orbital charge transfer between the Ni dopants and the surrounding carbon atoms. The resultant local structure with empty C–Ni hybrid orbitals is catalytically active and electrochemically stable.     

Multiple Phases of Molybdenum Carbide as Electrocatalysts for the Hydrogen Evolution Reaction

Molybdenum carbide has been proposed as a possible alternative to platinum for catalyzing the hydrogen evolution reaction (HER). Previous studies were limited to only one phase, β‐Mo₂C with an Fe₂N structure. Here, four phases of Mo‐C were synthesized and investigated for their electrocatalytic activity and stability for HER in acidic solution. All four phases were synthesized from a unique amine–metal oxide composite material including γ‐MoC with a WC type structure which was stabilized for the first time as a phase pure nanomaterial. X‐ray photoelectron spectroscopy (XPS) and valence band studies were also used for the first time on γ‐MoC. γ‐MoC exhibits the second highest HER activity among all four phases of molybdenum carbide, and is exceedingly stable in acidic solution.     

二硫化钼纳米片/碳纳米纤维杂化材料的制备及其析氢性能

以碳纳米纤维（CNFs）作为负载基体和反应器采用静电纺丝技术和碳化工艺生长和调控二硫化钼（MoS₂）纳米片。通过改变前驱体溶液浓度来调控纳米片的形貌和结构,利用MoS₂纳米片的高催化活性和CNFs高比表面积、良好的稳定性以及高电导率的协同作用,研究不同形貌和结构的杂化纳米材料在电催化析氢方面的应用,探索杂化材料形貌与性能之间的潜在规律。运用多种分析测试技术对制备得到的纳米杂化材料进行表征,并对所制备的MoS₂/CNFs杂化材料的电催化析氢性能（HER）进行研究,研究表明近似皮芯结构的MoS₂/CNFs-10杂化材料的电催化析氢性能最好,初始析氢过电位在220 mV,Tafel斜率为110 mV·dec^-1。     

二硫化钼纳米片/碳纳米纤维杂化材料的制备及其析氢性能

以碳纳米纤维(CNFs)作为负载基体和反应器采用静电纺丝技术和碳化工艺生长和调控二硫化钼(MoS_2)纳米片。通过改变前驱体溶液浓度来调控纳米片的形貌和结构,利用MoS_2纳米片的高催化活性和CNFs高比表面积、良好的稳定性以及高电导率的协同作用,研究不同形貌和结构的杂化纳米材料在电催化析氢方面的应用,探索杂化材料形貌与性能之间的潜在规律。运用多种分析测试技术对制备得到的纳米杂化材料进行表征,并对所制备的MoS_2/CNFs杂化材料的电催化析氢性能(HER)进行研究,研究表明近似皮芯结构的MoS_2/CNFs-10杂化材料的电催化析氢性能最好,初始析氢过电位在220 mV,Tafel斜率为110m V·dec~(-1)。     

TiO2 nanorods based self-supported electrode of 1T/2H MoS2 nanosheets decorated by Ag nano-particles for efficient hydrogen evolution reaction

Molybdenum disulfide (MoS₂) has shown significant promise as an economic hydrogen evolution reaction (HER) catalyst for hydrogen generation, but its catalytic performance is still lower than noble metal-based catalysists. Herein, a silver nanoparticles (Ag NPs)-decorated 1T/2H phase layered MoS₂ electrocatalyst grown on titanium dioxide nanorod arrays (Ag NPs/1T(2H) MoS₂/TNRs) was prepared through acid-tunable ammonium ion intercalation. Taking advantage of MoS₂ layered structure and crystal phase controllability, as-prepared Ag NPs/1T(2H) MoS₂/TNRs exhibited ultrahigh HER activity. As-proposed strategy combines facile hydrogen desorption (Ag NPs) with efficient hydrogen adsorption (1T/2H MoS₂) effectively circumventes the kinetic limitation of hydrogen desorption by 1T/2H MoS₂. The as-prepared Ag NPs/1T(2H) MoS₂/TNRs electrocatalyst exhibited excellent HER activity in 0.5 mol/L H₂SO₄ with low overpotential (118 mV vs. reversible hydrogen electrode (RHE)) and small Tafel slope (38.61 mV/dec). The overpotential exhibts no obvious attenuation after 10 h of constant current flow. First-principles calculation demonstrates that as-prepared 1T/2H MoS₂ exhibit a large capacity to store protons. These protons can be subsequently transferred to Ag NPs, which significantly increases the hydrogen coverage on the surface of Ag NPs in HER process and thus change the rate-determining step of HER on Ag NPs from water dissociation to hydrogen recombination. This study provides a unique strategy to improve the catalytic activity and stability for MoS₂-based electrocatalyst.     

Ultrafine Molybdenum Carbide Nanoparticles Composited with Carbon as a Highly Active Hydrogen‐Evolution Electrocatalyst

The replacement of platinum with non‐precious‐metal electrocatalysts with high efficiency and superior stability for the hydrogen‐evolution reaction (HER) remains a great challenge. Herein, we report the one‐step synthesis of uniform, ultrafine molybdenum carbide (Mo₂C) nanoparticles (NPs) within a carbon matrix from inexpensive starting materials (dicyanamide and ammonium molybdate). The optimized catalyst consisting of Mo₂C NPs with sizes lower than 3 nm encapsulated by ultrathin graphene shells (ca. 1–3 layers) showed superior HER activity in acidic media, with a very low onset potential of ?6 mV, a small Tafel slope of 41 mV dec^?1, and a large exchange current density of 0.179 mA cm^?2, as well as good stability during operation for 12 h. These excellent properties are similar to those of state‐of‐the‐art 20 % Pt/C and make the catalyst one of the most active acid‐stable electrocatalysts ever reported for HER.     

Boron-Dependency of Molybdenum Boride Electrocatalysts for the Hydrogen Evolution Reaction

Molybdenum-based materials have been considered as alternative catalysts to noble metals, such as platinum, for the hydrogen evolution reaction (HER). We have synthesized four binary bulk molybdenum borides Mo₂B, α-MoB, β-MoB, and MoB₂ by arc-melting. All four phases were tested for their electrocatalytic activity (linear sweep voltammetry) and stability (cyclic voltammetry) with respect to the HER in acidic conditions. Three of these phases were studied for their HER activity and by X-ray photoelectron spectroscopy (XPS) for the first time; MoB₂ and β-MoB show excellent activity in the same range as the recently reported α-MoB and β-Mo₂C phases, while the molybdenum richest phase Mo₂B show significantly lower HER activity, indicating a strong boron-dependency of these borides for the HER. In addition, MoB₂ and β-MoB show long-term cycle stability in acidic solution.     

Defect-enriched heterointerfaces N–MoO2–Mo2C supported Pd nanocomposite as a novel multifunctional electrocatalyst for oxygen reduction reaction and overall water splitting

Developing highly efficient, cost-saving, and durable multifunctional electrocatalysts for oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER) continues to be a significant challenge in the energy field. In this work, we decide to prepare an unusual multifunctional electrocatalyst, such as icosahedral palladium nanocrystals (PdNCs) encapsulating on N–MoO₂–Mo₂C half-hollow nanotube (HHNT) heterointerface, using an in-situ chemical reaction and following sonic probe irradiation method. All the experiments demonstrate that special defect-enriched heterointerfaces N–MoO₂–Mo₂C supported Pd nanocomposite can greatly improve the ORR activity (E_onset = 1.01 V and E_1/2 = 0.90 V) with good stability, outstanding HER (η₁₀ = 65 mV) and OER (η₁₀ = 180 mV) performances than those of commercial precious electrocatalysts (Platinum on carbon [Pt/C] and ruthenium oxide [RuO₂]). The overall water splitting electrolyzer fabricates by Pd/N–MoO₂–Mo₂C as both anode and cathode electrodes to achieve a current density of 10 Ma/cm² at a cell voltage of 1.56 V, which surpasses the most recent reported electrocatalysts.     

Coupling Mo2C with Nitrogen‐Rich Nanocarbon Leads to Efficient Hydrogen‐Evolution Electrocatalytic Sites

In our efforts to obtain electrocatalysts with improved activity for water splitting, meticulous design and synthesis of the active sites of the electrocatalysts and deciphering how exactly they catalyze the reaction are vitally necessary. Herein, we report a one‐step facile synthesis of a novel precious‐metal‐free hydrogen‐evolution nanoelectrocatalyst, dubbed Mo₂C@NC that is composed of ultrasmall molybdenum carbide (Mo₂C) nanoparticles embedded within nitrogen‐rich carbon (NC) nanolayers. The Mo₂C@NC hybrid nanoelectrocatalyst shows remarkable catalytic activity, has great durability, and gives about 100 % Faradaic yield toward the hydrogen‐evolution reaction (HER) over a wide pH range (pH 0–14). Theoretical calculations show that the Mo₂C and N dopants in the material synergistically co‐activate adjacent C atoms on the carbon nanolayers, creating superactive nonmetallic catalytic sites for HER that are more active than those in the constituents.