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.     

Significantly enhanced electrocatalytic activity of copper for hydrogen evolution reaction through femtosecond laser blackening

In this work, we report on the creation of a black copper via femtosecond laser processing and its application as a novel electrode material. We show that the black copper exhibits an excellent electrocatalytic activity for hydrogen evolution reaction (HER) in alkaline solution. The laser processing results in a unique microstructure: microparticles covered by finer nanoparticles on top. Electrochemical measurements demonstrate that the kinetics of the HER is significantly accelerated after bare copper is treated and turned black. At ?0.325 V (v.s. RHE) in 1 M KOH aqueous solution, the calculated area-specific charge transfer resistance of the electrode decreases sharply from 159 Ω cm² for the untreated copper to 1 Ω cm² for the black copper. The electrochemical surface area of the black copper is measured to be only 2.4 times that of the untreated copper and therefore, the significantly enhanced electrocatalytic activity of the black copper for HER is mostly a result of its unique microstructure that favors the formation and enrichment of protons on the surface of copper. This work provides a new strategy for developing high-efficient electrodes for hydrogen generation.     

Facile synthesis of carbon encapsulated RuO2 nanorods for supercapacitor and electrocatalytic hydrogen evolution reaction

In this work, carbon encapsulated RuO₂ nanorods (RuO₂ NRs/C) has been synthesized by thermolysis of ruthenium chloride and Punica granatum (P. granatum) peel under N₂ atmosphere. The synthesized RuO₂ NRs/C was characterized using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction method (XRD), field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) with energy dispersive spectroscopy (EDS) analyses. The FT-IR results suggested that the organic constituents of P. granatum have been carbonized and encapsulated over RuO₂ nanorods (RuO₂ NRs). The XRD pattern of RuO₂ NRs/C revealed its crystalline nature and carbon encapsulation. The synthesized RuO₂ NRs/C has been well dispersed with the average width of 20 nm, exposed from the FE-SEM and HR-TEM images. The EDS results of RuO₂ NRs/C showed the existence of three elements viz., Ru, O and C. Further, the supercapacitor and electrocatalytic hydrogen evolution reaction (HER) activities of RuO₂ NRs/C were studied using standard electrochemical methods. The synthesized RuO₂ NRs/C offered a maximum specific capacitance of 151.3 F g⁻¹ at a scan rate of 5 mV s⁻¹, obtained from the cyclic voltammetry results. The onset over potential and Tafel slope of synthesized RuO₂ NRs/C for HER were −0.099 V_RHE and −99.4 mV dec⁻¹, respectively. The present study revealed that RuO₂ NRs/C as a better candidate for supercapacitor and HER.     

MoS2/Mo2TiC2Tx supported Pd nanoparticles as an efficient electrocatalyst for hydrogen evolution reaction in both acidic and alkaline media

Development of electrocatalytic hydrogen production technology is the key to solving environmental and energy problems. Two-dimensional material Mo₂TiC₂T_x (T_x = –OH, –F) has shown great potential in electrocatalytic hydrogen evolution because of its excellent conductivity and hydrophilicity. However, due to the lack of sufficient active sites of Mo₂TiC₂T_x itself, its practical applications in electrocatalytic hydrogen evolution are limited. In this work, a highly-efficient hydrogen evolution electrocatalyst, namely Pd@MoS₂/Mo₂TiC₂T_x, is prepared through a simple pyrolysis method. In such a composite, the MoS₂ nanoflowers hybridized with the ammonia-treated Mo₂TiC₂T_x (MoS₂/Mo₂TiC₂T_x) are used as a substrate for loading a small number of Pd nanoparticles (4.27 at.%). Notably, the introduction of Pd nanoparticles into MoS₂/Mo₂TiC₂T_x provides abundant active sites for the hydrogen evolution reaction, improves the conductivity of the electrocatalyst, speeds up the adsorption and desorption of hydrogen, and induces a synergistic effect with the MoS₂. As a result, the Pd@MoS₂/Mo₂TiC₂T_x catalyst exhibits excellent electrocatalytic performance and remarkable stability in both acidic and alkaline media. In a 0.5 mol/L H₂SO₄ electrolyte, the overpotential of Pd@MoS₂/Mo₂TiC₂T_x was 92 mV with a Tafel slope of 60 mV/dec at a current density of 10 mA/cm². Meanwhile, the catalyst displayed an overpotential of 100 mV associated with a Tafel slope of 80 mV/dec at the current density of 10 mA/cm² in a 1 mol/L KOH electrolyte. This work shows the great potential of using Mo₂TiC₂T_x-based material in the field of electrocatalysis.     

Nitrogen-doped cobalt sulfide as an efficient electrocatalyst for hydrogen evolution reaction in alkaline and acidic media

The enhancement in intrinsic catalytic activity and material conductivity of an electrocatalyst can leads to promoting HER activity. Herein, a successful nitrogenation of CoS₂ (N–CoS₂) catalyst has been investigated through the facile hydrothermal process followed by N₂ annealing treatment. An optimized N–CoS₂ catalyst reveals an outstanding hydrogen evolution reaction (HER) performance in alkaline as well as acidic electrolyte media, exhibiting an infinitesimal overpotential of ?0.137 and ?0.097 V at a current density of ?10 mA/cm² (?0.309 and ?0.275 V at ?300 mA/cm²), corresponding respectively, with a modest Tafel slope of 117 and 101 mV/dec. Moreover, a static voltage response was observed at low and high current rates (?10 to ?100 mA/cm²) along with an excellent endurance up to 50 h even at ?100 mA/cm². The excellent catalytic HER performance is ascribed to improved electronic conductivity and enhanced electrochemically active sites, which is aroused from the synergy and mutual interaction between heteroatoms that might have varied the surface chemistry of an active catalyst.     

Hierarchical MoS2 nanosheets integrated Ti3C2 MXenes for electrocatalytic hydrogen evolution

In this study, conductive Ti₃C₂ MXenes were used as a promoter to accelerate charger transfer of MoS₂, realizing highly efficient HER electrocatalysis. A facile hydrothermal strategy is demonstrated to be effective for in situ growth of MoS₂ nanosheets vertically standing on planar Ti₃C₂ nanosheets to form hierarchical heterostructures. Beneficial from the opened layer structures and strong interfacial coupling effect, the resulting MoS₂/Ti₃C₂ heterostructures achieve a giant enhancement in HER activity compared with pristine MoS₂ nanosheets. More specifically, the catalytic current density induced by MoS₂/Ti₃C₂ heterostructures at an overpotential of ∼400 mV is nearly 6.2 times as high as that of the pristine MoS₂ nanosheets. This work uncovers that the Ti₃C₂ nanosheets are ideal candidates for construction of highly active electrocatalysts for water splitting.     

CuFe electrocatalyst for hydrogen evolution reaction in alkaline electrolysis

The development of high performance, stable catalyst with non-precious metals for electrochemical hydrogen evolution reaction for alkaline electrolysis is in demand. Here-in, we report the synthesis of CuFe layered double hydroxide (LDH) electrocatalyst on nickel foam via facile hydrothermal method. In alkaline electrolysis with 1 M NaOH electrolyte, CuFe LDH as cathode requires an overpotential of 159 mV to generate current density of 10 mA cm⁻². Which is ca. 51 mV and 7 mV lower than NiFe LDH and NiRu LDH. CuFe LDH exhibits significant electrocatalytic activity for HER. The higher catalytic activity of CuFe LDH compared to NiFe LDH may be achieved with higher proton adsorption by Cu compared to Ni. Also, the efficient charge transfer with interconnected LDH layers, favourable three dimensional structure facilitating easy electrolyte transfer to the active sites and hydrogen gas diffusion. This work may help in developing low cost and efficient hydroxide catalyst.     

Mechanism of transition metal cluster catalysts for hydrogen evolution reaction

Studying the hydrogen evolution reaction (HER) catalyst is important for the global energy crisis. Clusters have many special characteristics due to quantum size effect and super high specific surface area, including optical performance, catalytic performance, etc. In this work, the structures of transition metal cluster TM_n (TM = Co, Ni, Cu, Pd, Pt, n = 4–10) were searched and optimized by quantum chemistry methods. To search for non-precious metal catalysts, we calculated the Gibbs free energies for HER process on different clusters. Furthermore, the electronic structures of clusters before and after the reaction with H were analyzed, including the molecular surface electron distribution, the frontier molecular orbital, and the charge transfer properties, which dominated the HER processes. The results show that the Cu clusters have excellent HER catalytic properties due to its suitable surface electron distribution and HOMO/LUMO levels, especially Cu₄, Cu₇ and Cu₉, which even comparable to Pt catalysts. These results can help us better understand the mechanism of clusters catalyze HER process.     

MoS2 supported CoS2 on carbon cloth as a high-performance electrode for hydrogen evolution reaction

Here we report a strategy to prepare electrocatalysts for hydrogen generation based on MoS₂ grown on highly conductive CoS₂ decorated carbon cloth (MoS₂/CoS₂/CC) through a two-step method. The rational design of sandwich structure of MoS₂/CoS₂/CC electrode was significant for homogenously dispersing MoS₂ on the carbon substrate, tuning the properties of the MoS₂ and improving long-term durability. Benefiting from the sandwich structure with highly exposed edges, fast electron transport and additional active sites brought by interfacial sulfur of MoSCo, the resulting MoS₂/CoS₂/CC electrode exhibited superior HER activity and excellent stability in acid solution including an overpotential of 118 and 159 mV at current density of 10 and 100 mA/cm², respectively, a Tafel slope of 37 mV per decade and excellent cycling stability in acid solution. The high catalytic performance and simplicity of the preparation method suggest applicability of the MoS₂/CoS₂/CC electrode for large-scale practical applications.     

Metal-organic frameworks derived N,S,O-doped carbon sheets coated CoP/Co3S4 hybrids for enhanced electrocatalytic hydrogen evolution reaction

Evidence shows that embedding metal-based hybrid into carbon matrix is an up-and-coming method to improve the efficiency and decrease the cost of electrocatalysts. Herein, by using a metal-organic framework (MOF) with 4,4-bipyridine and 2,5-thiophenedicarboxylic acid as a precursor, a CoP/Co₃S₄ hybrid embedded into N, S, O-doped carbon sheets (CoP/Co₃S₄@NSOC) was constructed through pyrolysis and phosphorization processes. The lamellar morphology, hetero-atom doping, and graphite carbon were favorable for fast electron and mass transfer. Moreover, the strong intrinsic activities of CoP and Co₃S₄ promoted electrocatalytic performance. In the electrochemical experiments, CoP/Co₃S₄@NSOC showed the lowest overpotential of 132 mV@10 mA cm^?2 for hydrogen evolution reaction (HER) among all the precursors. In addition, the electrocatalytic activity and structure of CoP/Co₃S₄@NSOC exhibited long-term stability over 60 h. The present work provides a feasible strategy for the construction of robust MOF-derived electrocatalysts.     

Interfaces engineering of MoNi-based sulfides electrocatalysts for hydrogen evolution reaction in both acid and alkaline media

Searching for efficiently noble-metal-free hydrogen evolution catalysts is critical to the development of hydrogen energy. In this work, we report an in-situ growing defect-rich heterointerfaces structure MoNi-based sulfides on carbon cloth via a facile and controllable hydrothermal process. The interface structure in MoNiS@NiS/CC can not only provide suffcient channel for transportation of electrolyte, but also release of produced gases in the catalytic process, thence enhance the sluggish hydrogen evolution efficiency. Furthermore, the defects in MoNiS@NiS/CC have significant impacts on hydrogen evolution behavior. Therefore, the as-synthesied MoNiS@NiS/CC shows a low overpotential of 33 mV to deliver a current density of 10 mAcm⁻² and a small tafel slope of 80 mVdec⁻¹, and also exhibits an excellent long-term stability in 0.5 M H₂SO₄. Additionaly, the MoNiS@NiS/CC offers outstanding hydrogen evolution reaction performances in 1 M KOH.     

Effect of copper addition on cobalt-molybdenum electrodeposited coatings for the hydrogen evolution reaction in alkaline medium

Co–Mo materials have been reported as electrocatalysts that present good performance in alkaline electrolytes. In this paper, the addition of copper into Co–Mo catalysts was evaluated for the hydrogen evolution reaction (HER). It was observed that the electrochemical activity of the Co–Mo for the HER benefited from the addition of copper. The overpotentials required to reach a current density of −10 mA cm⁻² were of −156 mV and −119 mV for Co₆₇Mo₃₃ and Co₅₆Mo₂₁Cu₂₃, respectively. Besides the increased surface area resulting from the addition of copper, it was observed that the improved intrinsic activity for Co₆₁Mo₃₂Cu₇, compared to Co₆₇Mo₃₃, is related to a thermodynamic favoring of the hydrogen adsorption and desorption stages. Large quantities of copper do not favor the HER; therefore, the increased catalytic activity depends on a balance between the intrinsic catalytic activity and the increase of the electroactive area.     

Phytic acid-coated titanium as electrocatalyst of hydrogen evolution reaction in alkaline electrolyte

The phytic acid-coated titanium (IP6/Ti) electrode was prepared through a simple drop-drying process, with an aim of improving electrocatalytic activity toward the hydrogen evolution reaction (HER). Scanning electron microscope and X-ray photoelectron spectroscopy showed that the IP6 coated the substrate surface uniformly and completely. Evaluation of the electrode activity was carried out in 1.0 M NaOH by linear polarization, electrochemical impedance spectroscopy (EIS) and chronopotentiometry. The kinetic parameters obtained from Tafel curves reveal that the IP6 coating can enhance the exchange current density of the HER by 489 times compared to the bare Ti, and reduce the HER activation energy by nearly 50%. The EIS data prove that the charge transfer resistance of the HER was considerably reduced due to the IP6 coating, with a decrease in real surface area of the electrode. The catalytic effect of IP6 is due to an improvement in the charge transfer kinetics of the HER. This work indicates that IP6 may be a potent candidate as a catalyst for hydrogen energy production.     

Facile in-situ formation of high efficiency nanocarbon supported tungsten carbide nanocatalysts for hydrogen evolution reaction

Electrochemical hydrogen evolution reaction (HER) is one of the key techniques for hydrogen production. Much great effort has been made so far to develop highly efficient HER catalysts to replace expensive precious metals (e.g. Pt). Unfortunately, the synthesis processes were generally not cost-effective and/or scalable. So it is highly desirable to develop a facile technique to enhance HER activity of conventional inexpensive but less active materials. In this work, monodispersed tungsten carbide (WC) nanoparticles (<5 nm) were in-situ formed/anchored on nanosized carbon black (CB) and carbon nanotube (CNT) via a simple low temperature molten salt synthesis technique. Owing to this special hybrid structure, both the exposed surface area of active species and the electrical conductivity of the catalysts were increased effectively, making the catalysts perform considerably better in HER than pure WC and WC based catalysts prepared via other conventional routes. WC nanocrystals in-situ formed/anchored on CNTs showed small onset overpotential (90 mV), low Tafel slope (69 mV dec^?1), high current density (93.4 and 28 mA cm^?2 at 200 and 300 mV, respectively) and excellent stability (remaining stable even after 3000 cycles). Such a performance is one of the best among those of WC based electrocatalysts developed to date. We demonstrate here significantly improved HER performances of inexpensive tailored WC materials, along with a facile synthesis strategy which could be also readily extended to prepare a range of other types of mono-dispersed nanocatalysts for more potential applications.     

High-performance alkaline hydrogen evolution of NiMoP2 nanowire boosted by bimetallic synergic effect

Hydrogen evolution reaction (HER) in alkaline conditions usually requires a higher overpotential compared with acidic conditions due to the extra energy barrier originating from the additional water dissociation step. In this work, the theoretical calculation has confirmed that this challenge can be solved by the bimetallic synergic effect on binary transition metal catalysts. We report a simple method to synthesize NiMoP₂ nanowires with (100) plane which can precisely expose Ni and Mo atom. The synthesized NiMoP₂ nanowires exhibit a small overpotential of 87 mV to reach 10 mA cm⁻² with a low Tafel slope of 66 mV dec⁻¹ and long-term stability in alkaline solutions.     

Synthesis of Co2FeAl alloys as highly efficient electrocatalysts for alkaline hydrogen evolution reaction

The development of cost-effective non-precious metal electrocatalysts is a major challenge for water splitting applications, but it is important for the realization of renewable energy systems. Alloying has proved an effective way to design metal-based electrocatalysts, and by controlling the annealing temperature, the surface morphology and crystallinity of the alloy can be tuned to control the hydrogen evolution reaction (HER) performance. In this work, with a simple coprecipitation method, we have prepared Co₂FeAl alloys at different annealing temperatures (550 °C–670 °C), which exhibit excellent crystallinity and electrocatalytic performance for HER in alkaline solution. Among all conditions, the Co₂FeAl alloys prepared at 620 °C shows the better crystallinity and the higher purity, and it could achieve a low overpotential of 149 mV at 10 mA cm^?2 in alkaline solution. The overpotential demonstrates persistent stability with only 3 mV change after over 1000 cycles. Both density functional theory (DFT) calculations and experimental results revealed that alloying optimizes the electronic structure near the Fermi surface of the system, improving the electron transport efficiency and enhancing the catalytic activity. These Co₂FeAl alloys are appealing candidates for high-performance alkaline HER electrocatalytic electrodes in water electrolysis due to their outstanding electrocatalytic properties.     

Facile and large-scale preparation of Co/Ni-MoO2 composite as high-performance electrocatalyst for hydrogen evolution reaction

Facile fabrication of high-performance catalyst based on low-cost metals for sustainable hydrogen evolution is still a matter of cardinal significance. However, synthetic approaches for electrocatalyst are usually complicated and the yields are often low. Herein, we report a one-step simple method for the large-scale synthesis of Co/Ni-MoO₂ composite as efficient and stable hydrogen evolution reaction (HER) electrocatalyst to drive 10 mA cm^?2 current density with a low overpotential of 103 mV in basic media. Co-MoO₂ and Ni-MoO₂ were also prepared using this method with overpotential of 137 and 130 mV, respectively, to gain the same current density. These results indicate that this facile synthesis approach is of great practical importance as it can be easily used for large-scale preparation of electrocatalysts in industry.     

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.     

Application of transition metal high entropy boride in electrocatalytic hydrogen evolution reaction

For the growth of hydrogen energy, it is essential to create electrocatalysts that are affordable, effective, and stable. The transition metal high-entropy boride electrocatalyst is synthesized with the molten salt-assisted boron thermal reduction method. It discusses the influence of element composition, temperature, and the ratio of salt to material on electrocatalytic hydrogen evolution. The results show that WMoVNbMnB synthesized at the ratio of salt to material of 15:1 and sintering temperature of 1000 °C has nano-flake structure. The overpotential at a current density of 10 mA cm⁻² at 1 M KOH is as low as 115 mV, with the Tafel slope of 92 mV·dec⁻¹. According to theoretical study, the transition metals (V, Mo, and Mn) are a considerable contributor to the electron around the Fermi level. Under the synergistic effect of multiple components, the V 3d orbit possesses excellent polarization, which thus improves the migration ability of the carrier. In the process of water decomposition, WMoVNbMnB electrocatalyst only needs to cross the 0.24 eV energy barrier to successfully dissociation, with the excellent properties of a glass carbon catalyst. It offers a workable reference for creating water electrolysis technology because of its highly effective catalytic activity.