Ru/MoO2 decorated on CNT networks as an efficient electrocatalyst for boosting hydrogen evolution reaction

Generally, electrochemical hydrogen evolution reaction (HER) is hampered by slow kinetics and low round-trip efficiency. Electrocatalysts with a hierarchical structure and large surface area are expected to overcome these problems. Herein, we prepared a Ru/MoO₂/carbon nanotubes (RMC) hybrid with a hierarchical structure by a convenient solid-phase reaction (SPR) method, and studied the electrochemical activity for HER. After annealing as-prepared RuO₂/MoO₂/carbon nanotubes (ROMC) precursor in a tubular furnace under Ar atmosphere, RuO₂ and MoS₂ were in-situ transformed into Ru metal and MoO₂ phase by the redox SPR. Through various tests, we have confirmed that the new formed Ru metal and MoO₂ phase are combined and uniformly coated on the outer surface of CNTs. Interestingly, the RMC-500 exhibits the best HER performance with a low overpotential of 16 mV at l0 mA cm^?2, small Tafel slope of 45 mV dec^?1, higher electrochemical active surface area, and long-time durability in alkaline electrolyte.     

3d transitional-metal single atom catalysis toward hydrogen evolution reaction on MXenes supports

Single atom catalysis involving atomically dispersed metal active sites on the appropriate supports is the effective way to magnify the catalytic efficiency and reduce the cost. By performing the first-principles calculations, we studied the anchoring of 3d transitional-metal single atoms M (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) on the surfaces of MXenes Cr₂CO₂ and Mo₂CO₂ and the catalytic activity of the single atom sites for hydrogen evolution reaction (HER). Sixteen single atom sites, M-Cr₂CO₂ (M = Sc, Ti, V, Cr, Mn, Fe, Co, Cu and Zn) and M-Mo₂CO₂ (M = Sc, Ti, V, Cr, Mn, Fe and Zn) have been chosen via examining the energetical and thermal stability of the isolated M atoms on the substrates. More importantly, we have calculated the Gibbs free energy change (ΔG_H) of H adsorption on the surface of M anchored Cr₂CO₂ and Mo₂CO₂ and find that Cr, Fe, Zn on Cr₂CO₂ and Sc, V on Mo₂CO₂ are the promising single atom active sites toward HER. Additionally, our results show that M atoms adsorbing turns the nearby sites to be active for catalyzing HER. MXenes Cr₂CO₂ and Mo₂CO₂, in terms of the supporting not only stabilize but also works together with the anchored single atom M as active catalyst toward HER.     

The hydrogen evolution reaction on single crystal gold electrode

As one of the important candidate of power sources for the future, the research and production of hydrogen gas has a significant importance. In this article, the emphasis is on the influence of impurities on hydrogen evolution reaction, i.e., the influence of an addition of decacyclene, C₁₂H₃₅C₆H₄SO₄Na, CH₃CH₂OH, chromanone, H₂SO₄, HNO₃, 4,4′-biphenediol and 1,2,3,4-tetraphenyl-1,3-cyclopentadiene was studied by electrochemical impedance technique. The adsorption structure for some organics was measured by scanning tunneling spectroscopy techniques. Superstructure of adsorbed decacyclene on Au(111) surface was captured. The ordered adsorption structure of 4,4′-biphenyldiol on Au(111) and (100) was also observed. The addition of decacyclene has shown an opposite effects on hydrogen evolution for Au(111) and (100) surface, i.e., it inhibits the reaction at Au(100) but enhances the one at Au(111). The results show that the addition of C₁₂H₃₅C₆H₄SO₄Na and HNO₃, especially the latter, can improve the hydrogen evolution. In the article the adsorption structure and hydrogen evolution reaction have been studied in order to give some useful information about the relation between the adsorption structure and the properties. The purpose of this article is to attempt to find the relation between electrochemical performance and the adsorption structure, and to explore the effect of some additives.     

Ultra-fine Ru nanoparticles decorated V2O3 as a pH-universal electrocatalyst for efficient hydrogen evolution reaction

Developing high-efficiency electrocatalysts viable for pH-universal hydrogen evolution reaction (HER) has attracted great interest because hydrogen is a promising renewable energy carrier for replacing fossil fuels. Herein, we present a facile strategy for fabricating ultra-fine Ru nanoparticles (NPs) decorated V₂O₃ on the carbon cloth substrates as efficient and stable pH-universal catalysts for HER. Benefiting from the metallic property and electronic conductivity of V₂O₃ matrix, the optimized hybrid (Ru/V₂O₃-CC) exhibits excellent HER activities in a wide pH range, achieving lower overpotentials of 184, 219, and 221 mV at 100 mA cm⁻² in 0.5 M H₂SO₄, 1.0 M KOH and 1.0 M phosphate-buffered saline, respectively. Moreover, the electrode remains superior stability with negligible degradation after 5000 cyclic voltammetry scanning whether in acidic, alkaline or neutral media. Experimental results, combined with theoretical calculations, demonstrate that the interaction between Ru NPs and the support V₂O₃ induces the local electronic density diversity, allowing optimization of the adsorption energy of Ru towards hydrogen intermediate H1, thus favoring the HER process.     

Redox active MoO3-Polyaniline hybrid composite for hydrogen evolution reaction and supercapacitor application

A simple oxidative polymerization approach has been used to synthesize MoO₃/PANI hybrid composite for energy conversion and storage application. In this carbon-free energy conversion process, as-developed electrocatalyst (MoO₃/PANI hybrid composite) has significantly improved the molecular hydrogen generation via electro-reduction of protons. The hydrogen evolution kinetics parameters, overpotential at 10 mA cm⁻² is ∼110 mV and Tafel slope 132 mV/dec have been obtained for the as-developed catalyst which suggests the reaction is controlled by Volmer-limited reaction step. Further the as-developed material has been tested for energy storage application and exhibited specific capacitance of 680 F. g⁻¹.     

Nickel phosphide decorated Pt nanocatalyst with enhanced electrocatalytic properties toward common small organic molecule oxidation and hydrogen evolution reaction: A strengthened composite supporting effect

In this paper, well-dispersed Ni₂P-NiP₂-Pt/CNTs catalyst promoted by nickel-phosphorus compounds was readily synthesized by a two-step hydrothermal process. The as-synthesized Ni₂P-NiP₂-Pt/CNTs displayed improved electrocatalytic properties towards electro-oxidation of common small organic fuels such as methanol, ethanol and formic acid in contrast with Pt/CNTs and Pt/CNPs in acidic electrolytes. Meanwhile, the Ni₂P-NiP₂-Pt/CNTs catalyst also exhibited the excellent performance toward hydrogen evolution reaction with a more negative onset potential (?15 mV) and a smaller Tafel slope (29.8 mV dec^?1) when compared with Pt/CNTs (?29 mV, 30.6 mV dec^?1) and Pt/CNPs (?32 mV, 31.3 mV dec^?1) in 1.0 M H₂SO₄ solution. The catalytic activity enhancement possibly derives from the induced large specific surface area of carbon nanotubes as well as the strengthened synergistic effect between multiple supporting interactions.     

Flower-like CoS2/MoS2 nanocomposite with enhanced electrocatalytic activity for hydrogen evolution reaction

Molybdenum sulfide (MoS₂) has received tremendous attracts for its promising performance in the aspects of hydrogen evolution reaction (HER). To improve the HER activity of MoS₂, we designed a flower-shaped CoS₂/MoS₂ nanocomposite with enhanced HER electroactivity compared with MoS₂ nanosheets by a simple one-step hydrothermal method. The facile approach brings about distinct transformation of the morphology from nanosheets to nanoflower structures. The introduction of Co element into MoS₂ results in the larger active surface area, more edge-terminated structures, and higher conductivity of the CoS₂/MoS₂ nanocomposite, which are good for improving the HER electroactivity. In brief, the optimized catalyst exhibits the low overpotential of 154 mV at 10 mA cm^?2, small Tafel slope of 61 mV dec^?1, and excellent stability in acidic solution.     

Biomass-derived carbon nanosheets coupled with MoO2/Mo2C electrocatalyst for hydrogen evolution reaction

Transition metal carbide such as molybdenum carbide has been widely used in electrolytic water for hydrogen production due to its potential catalytic property. The synthesis of molybdenum carbide-based high-efficient catalysts by simple process remains great challenges. Herein, Mo oxide/carbide material with hybrid morphology was synthesized by carbonizing mixture of lotus roots and Mo salt. The as-obtained material consists of MoO₂/Mo₂C (MOMC) anchored on biomass-derived nitrogen-doped carbon (NC) matrix. The results show that as-prepared material displays leaf-like and belt-like nanosheets, and the MOMC/NC catalyst with optimal Mo contents exhibits an excellent activity with a low overpotential of 138 mV to drive 10 mA cm^?2 and Tafel slope is 56.7 mV dec^?1 in alkaline medium, indicating that as-prepared catalyst will have promising application in the field of catalysis.     

Ni-W nanostructure well-marked by Ni selective etching for enhanced hydrogen evolution reaction

Designing active, stable and affordable electrocatalysts is a promising pathway for fulfilling the mankind's dream of preserving unsustainable fuel sources. Herein, the facile utilization of Romanesco-like and arrow-like nanostructures of Ni-W samples is introduced. Exclusive emphasis is placed on achievement of the unique nanostructure through cost-effective, repeatable and readily accessible two-step techniques, i.e. Ni-W electrodeposition approach followed by etching treatment. Microscopic study was fully utilized for surface morphology and structural investigation. The electrochemical analysis was used to evaluate the electrocatalytic activity and stability. The surface roughness of the Ni-W film electrodeposited by D.C = 90% and etched via acidic solution was up to 93.85, considerably higher than that of the Ni-W electrodeposited by D.C = 20% and without etched Ni-W films (55.36 and 41.51 respectively). Therefore, HER activity was improved with η₁₀ and η₂₀ of 169 and 226 mV vs. RHE, respectively, due to higher effective active surface for H⁺ adsorption. The Tafel slope analysis suggests Volmer mechanism as the HER rate-determining step. The electrochemically active surface area was also enhanced from roughly 2 to 10 cm². In addition, wettability was investigated by a contact angle of less than 65°, which indicates high penetration of electrolyte to the nanostructure. Rapid separation of bubbles on the arrow-like nanostructure of Ni-W films exhibited unstable H₂ bubbles on surface of the electrode.     

Synthesis of nitrogen-doped MoSe2 nanosheets with enhanced electrocatalytic activity for hydrogen evolution reaction

Benefiting from improved electrical conductivity, the N-doped MoSe₂ nanosheets show substantially enhanced HER activity with a lower onset overpotential of approximately ?135 mV and a smaller Tafel slope of 62 mV dec^?1, which exhibiting enhanced catalytic performance compared with that of pure MoSe₂. The success of improving the HER performance via the introduction of N dopant offers a new opportunity in the development of high performance MoSe₂-based electrocatalyst.     

Copper induced phosphide for enhanced electrochemical hydrogen evolution reaction

Research on highly efficient catalysts for electrochemical hydrogen evolution reaction (HER) remains a challenge. In this work, we successfully wrap copper (Cu) inside of copper phosphide (Cu₃P) nanoparticle to form a copper/copper phosphide (Cu/Cu₃P) core/shell structure attached on carbon nanotubes (CNTs) for enhanced HER activity in acid. The average size of the core/shell particles is around 25 nm, with about 5 nm of Cu₃P as the outer layer. The catalytic activity of the core/shell structure is significantly promoted compared to the metallic Cu and Cu₃P pure phases nanoparticles on CNTs, requiring overpotentials of 84 and 161 mV to achieve 10 and 100 mA cm⁻² of current density, respectively. The core/shell structure also presents high HER durability and stability, with the polarization curve overlapped after 5000 cycles of CVs and steady current density at 25 mA cm⁻² for as long as 10 h. To account for the promoted HER performance, the Cu/Cu₃P structure is fully investigated by physical and electrochemical characterizations and density functional theory (DFT) calculations. The DFT results depict that the neutralized the adsorption Gibbs free energy of hydrogen atoms (ΔG_H1) is induced by the electronic interactions between metallic Cu and phosphide phase.     

Quasi zero-dimensional MoS2 quantum dots decorated 2D Ti3C2Tx MXene as advanced electrocatalysts for hydrogen evolution reaction

Developing advanced noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) is still a great challenge. Herein, a novel HER catalyst with quasi zero-dimensional (0D) MoS₂ quantum dots (QDs) supported on two-dimensional (2D) Ti₃C₂T_x MXene nanosheets is facilely synthesized. The MoS₂ QDs/Ti₃C₂T_x nanohybrid retains the unique layer structure, and the MoS₂ QDs are in situ formed and distributed uniformly. The obtained MoS₂ QDs/Ti₃C₂T_x catalyst exhibits superior electrocatalytic activity due to its excellent conductivity, abundant of active sites exposed and a high percentage of 1T metallic phase (～76%) of MoS₂ QDs. Remarkably, an early HER overpotential of 220 mV at 10 mA cm^?2 and a small Tafel slope of 72 mV dec^?1 of MoS₂ QDs/Ti₃C₂T_x are achieved in 0.5 M H₂SO₄ solution. In addition, the exchange current density of MoS₂ QDs/Ti₃C₂T_x is ～5 times larger compared with pure MoS₂, thus demonstrating an accelerated charge transfer during the electrocatalytic process.     

Vapor-assisted engineering heterostructure of 1D Mo3N2 nanorod decorated with nitrogen-doped carbon for rapid pH-Universal hydrogen evolution reaction

Reasonable construction of heterostructure is of significance yet a great challenge towards efficient pH-universal catalysts for hydrogen evolution reaction (HER). Herein, a facial strategy coupling gas-phase nitridation with simultaneous heterogenization has been developed to synthesize heterostructure of one-dimensional (1D) Mo₃N₂ nanorod decorated with ultrathin nitrogen-doped carbon layer (Mo₃N₂@NC NR). Thereinto, the collaborative interface of Mo₃N₂ and NC is conducive to accomplish rapid electron transfer for reaction kinetics and weaken the Mo–H_ads bond for boosting the intrinsic activity of catalysts. As expected, Mo₃N₂@NC NR delivers an excellent catalytic activity for HER with low overpotentials of 85, 129, and 162 mV to achieve a current density of 10 mA cm^?2 in alkaline, acidic, and neutral electrolytes, respectively, and favorable long-term stability over a broad pH range. As for practical application in electrocatalytic water splitting (EWS) under alkaline, Mo₃N₂@NC NR || NiFe-LDH-based EWS also exhibits a low cell voltage of 1.55 V and favorable durability at a current density of 10 mA cm^?2, even surpassing the Pt/C || RuO₂-based EWS (1.60 V). Consequently, the proposed suitable methodology here may accelerate the development of Mo-based electrocatalysts in pH-universal non-noble metal materials for energy conversion.     

Nickel nanocones as efficient and stable catalyst for electrochemical hydrogen evolution reaction

In this work, nickel nanocones (NNCs) were fabricated by single-step electrodeposition method. The NNCs were used as hydrogen evolution electrode and their electrocatalytic activity was compared with pure nickel film. Linear Sweep Voltammetry (LSV), Tafel polarization, Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV) and chronopotentiometry in 1 M KOH were used for study of the electrocatalytic activity for hydrogen evolution reaction (HER). The active surface area was increased by formation of NNCs and hence, the electrocatalytic activity of nickel electrode was improved. Results indicate that the current density corresponding to the amount of evolved hydrogen of NNCs is five times more than pure nickel film formed in the Watts bath.     

Tailoring the hydrophilic and hydrophobic reaction fields of the electrode interface on single crystal Pt electrodes for hydrogen evolution/oxidation reactions

Interfacial hydrophobic/hydrophilic reaction fields significantly affect various reactions at the electrode surface. The hydrogen evolution reaction (HER) and the hydrogen oxidation reaction (HOR) have been investigated on single crystal Pt electrodes modified with hydrophobic/hydrophilic cations and anion-exchange copolymers in alkaline solutions. In alkali metal hydroxide solutions, Pt (110) exhibits the highest HER/HOR activity in the low-index planes of Pt. On the low-index planes of Pt, the hydrophilicity of the alkali metal cation in the supporting electrolyte activates the HER/HOR depending on its hydration energy. Hydrophilic cations at the interface facilitate the extraction of hydrogen from the hydrated water. The modification of anion-exchange copolymers with a hydrophobic skeleton on Pt (110) further enhanced the HER/HOR activity. The hydrogen bonding network formed around the hydrophobic species facilitated the mobility of water molecules and the OH⁻ as the reactant/product of the HER/HOR. Appropriately forming hydrophilic and hydrophobic reaction fields at the interface improved the HER/HOR activity.     

P-doped 3D graphene network supporting uniformly vertical MoS2 nanosheets for enhanced hydrogen evolution reaction

In order to optimize the conductivity of molybdenum disulfide (MoS₂) and promote its large-scale application as a catalyst for hydrogen evolution, MoS₂ is usually used to form composites with conductive materials, but these hybrid materials suffer from scare active sites, overlapping and complicate process. In this work, phosphoric acid is used as a builder of stereoscopic structures, which can not only twist graphene sheets into a P-doped three-dimensional (3D) graphene network but also promote surface electron transport between graphene sheets. Without adding additional framework materials such as carbon nanotubes or nickel foam, stereoscopic MoS₂/graphene structures are formed with a large number of twisted graphene sheets to support the vertical growth of MoS₂ and expose the edge sites of MoS₂, showing a low Tafel slope about 35 mV dec⁻¹, a high current density of 900 mA cm⁻² at about 300 mV and a robust stability over 2000 cycles. Thus, this work shows a possibility to synthesize an efficient catalyst on a large-scale for hydrogen evolution reaction, which can promote the realization of hydrogen economy.     

Tailoring CoNi alloy embedded carbon nano-fibers by thiourea for enhanced hydrogen evolution reaction

Toward the evolution of structure and composition of transition-metal based catalysts for hydrogen evolution reaction (HER), thiourea is utilized to tailor the size and distribution of CoNi alloy nanoparticles embedded in electrospinning carbon nanofibers (CoNi@CNFs). When adding appreciate dose of thiourea in the electrospinning precursor, the average grain size of CoNi nanoparticles reduces from 19.4 to 10.2 nm by the steric barrier effect of thiourea. Meanwhile, thiourea controls the favorable growth of CoNi on the surface of CoNi@CNFs. The surface CoNi alloy content increases from 25.1 to 34.6 wt %. The refining and well-dispersed CoNi nanoparticles improve the graphitization degree of carbon substrates. Furthermore, Thiourea provides S doping in CoNi alloy as well as the S, N doping in carbon substrates. The evolution of the structure and composition of CoNi@CNFs catalyst boosts the electronical performances by effectively modulating the electronic structure of the active sites, enlarge the exposure of active sites, and facilitate the electron transfer and mass diffusion. As a result, the optimized CoNi@CNFs (Thu-1.0) shows remarkable low overpotential (116 mV, 10 mA cm^?2@1.0 mol KOH), outstanding hydrogen production rate (24.5 μmol/h, 20 mA cm^?2@1.0 mol KOH), and superior stability (7.8% overpotential enlargement after 5000 continuous linear voltammetric cycles), when used as a catalyst material for HER application.     

CoS2/MoS2 decorated with nitrogen doped reduced graphene oxide and multiwalled carbon nanotube 3D hybrid as efficient electrocatalyst for hydrogen evolution reaction

Designing an efficient and stable electrocatalyst made of earth abundant elements to take over expensive noble metal based for Hydrogen Evolution Reaction (HER) have been focused. Cobalt disulfide-molybdenum disulfide nanocomposite supported by nitrogen doped reduced graphene oxide and multiwalled carbon nanotubes (CoS₂/MoS₂@NrGO-MWCNT) is reported as an efficient electrocatalyst for HER. CoS₂/MoS₂@N-rGO-MWCNT and ternary hybrids composed of CoS₂, MoS₂ and N-rGO/MWCNT have been investigated. The catalysts were prepared by facile hydrothermal method, and the optimal doping ratio referred to date cobalt to molybdenum as 2:1 was chosen. It is found that co-existence of CoS₂, MoS₂ brings abundant active sites and incorporation of MWCNT offered stability. Good dispersion of CoS₂ nanoparticles on graphene and MoS₂ sheets is observed. Additionally nitrogen doping on rGO sheets has been carried out to boost up the electronegativity of the catalyst as a support to enhance the catalytic activity of CoS₂/MoS₂ for refine structure and better electrical conductance. Precisely, CoS2/MoS2@N-rGO-MWCNT exhibited smaller tafel slope 73 mV dec^?1 at overpotential 281 mV for current density 10 mA cm^?2 and the substantial stability of 14 h is recorded in 0.5 M H₂SO₄ medium, results suggest that catalyst is viable alternate for HER.     

Nano P zeolite modified with Au/Cu bimetallic nanoparticles for enhanced hydrogen evolution reaction

In the present study, the excellent catalytic performance of Au/Cu bimetallic nanoparticles based on nano P zeolite modified carbon paste electrode (Au/Cu-NPZ-CPE) as one of the most promising electrocatalyst toward hydrogen production is introduced. Herein, nano P zeolite is synthesized by using agriculture residues, stem sweep ash with purity approximately 80.205 wt% of SiO₂ which provides attractive economically silica source for the preparation of inexpensive zeolite. For the preparation of Au/Cu-NPZ-CPE, ion exchange protocol followed by galvanic replacement reaction was employed to result Au/Cu embedded zeolite framework. By evaluating the electrocatalytic activity of proposed catalyst with linear sweep voltammetry and Tafel polarization, a low overpotential of 100 mV and high exchange current density (2.51 mA cm⁻²) are demonstrated which compares favorably to most previously reported electrocatalysts for hydrogen evolution reaction. Owing to the inherent porosity of synthesized nano P zeolite, it successfully prevents the aggregation of bimetallic nanoparticles which promotes the hydrogen evolution reaction. Particularly, low Tafel slope for offered catalyst (33 mV dec⁻¹) demonstrates the acceleration of hydrogen evolution reaction kinetics owing to the increase in the number of accessible active sites. Tafel slope of Au/Cu-NPZ-CPE is 3, 5, 6, 6.5 and 7 times lower than that for Au-NPZ-CPE, Cu-NPZ-CPE, Au/Cu-CPE, NPZ-CPE and CPE, respectively, which shows the best electrocatalytic activity among other modified carbon paste electrodes. Furthermore, the corresponding long term stability test by chronoamperometry method indicates that the current density reaches to nearly 91% of its primary value (after 5500 s) which provides the favorable practical demands of the catalyst in hydrogen production.     

Fabrication of phosphorus-mediated MoS2 nanosheets on carbon cloth for enhanced hydrogen evolution reaction

Molybdenum sulfide (MoS₂) as a graphene-like sheet material has attracted wide attention owing to the potential for hydrogen evolution reaction (HER). However, the large-scale application of MoS₂ is still difficult due to the inherent poor conductivity and insufficient active edge sites. Herein, we develop a simple method to grow P-doped MoS₂ nanosheets on carbon cloth for high efficiency HER. The 2D carbon cloth can prevent the stacking of MoS₂ nanosheets and improve the conductivity with the doping of P atoms. As a result, the P–MoS₂/CC-300 shows the excellent electrocatalytic activity with an overpotential of 81 mV at 10 mA cm^?2 and the lower Tafel slope of 98 mV/dec. Furthermore, it also shows the good electrocatalytic durability for 15 h. This work provides an opportunity for the design of excellent and robust MoS₂-based catalyst via structural engineering and doping method.