CoSe2 nanoparticles grown on carbon nanofibers derived from bacterial cellulose as an efficient electrocatalyst for hydrogen evolution reaction

Exploration of high-efficiency and inexpensive Pt-free electrochemical catalysts for hydrogen evolution reaction (HER) is highly significative for carbon dioxide free energy conversion systems. In this work, we described the development of CoSe₂ nanoparticles grown on the carbon nanofibers (CNFs) derived from bacterial cellulose (CNFs/CoSe₂) through a facile one-step hydrothermal preparation, which not only showed a three-dimensional (3D) porous network structure, but also possessed large surface area. This rationally designed architecture realizes the uniform distribution of CoSe₂ nanoparticles to provide with fully exposed active edges and the unique conductive interwoven carbon nanofibers facilitates the charge transportation in HER process, thus leading to remarkable HER activity. As expected, the CNFs/CoSe₂ shows a low onset overpotential of ?85 mV, low overpotential (η₁₀ = 119 mV) for reaching a current density of ?10 mA cm^?2 and smaller Tafel slope of 54 mV dec^?1 as well as good cycling stability in acidic electrolyte.     

Porous CoS2 nanostructures based on ZIF-9 supported on reduced graphene oxide: Favourable electrocatalysis for hydrogen evolution reaction

The research and developments of porous, highly active non-noble metal cathode materials are the current hot spots. In our work, ZIF-9 (Zeolitic imidazolate framework-9) as a cobalt source provide porous structure, we have sulfurized the ZIF-9 into CoS₂ by a simple hydrothermal method. Ultimately, the porous CoS₂/RGO cathode material was obtained. Through a series of characterization analyses (powder X-ray diffraction, X-ray photoelectron spectroscopy), it is confirmed that the CoS₂/RGO composite was successfully formed. Furthermore, electrochemical tests demonstrated that the pursued catalyst exhibited remarkable hydrogen evolution reaction (HER) activities with a favorable overpotential (only 180 mV for 10 mA cm^?2 vs reversible hydrogen electrode), a low Tafel slopes (75 mV decade^?1) and high stability in acidic condition (more than 18 h).     

Mo incorporated W18O49 nanofibers as robust electrocatalysts for high-efficiency hydrogen evolution

Creation of robust and stable electrocatalysts is a persistent objective for high-efficiency hydrogen evolution by water splitting. We present here the experimental realization of one-dimensional Mo incorporated W₁₈O₄₉ nanofibers (NFs) by a template-free solvothermal method. When utilized as electrocatalysts for hydrogen evolution through water splitting, the preliminary results demonstrate that the optimized catalytic electrode from 1 at% Mo doped W₁₈O₄₉ NFs yields an onset overpotential of 89 mV and Tafel slope of 49 mV dec^?1 as well as maximal exchange current density up to 1.60 × 10^?2 mA cm^?2. An overpotential as low as 462 mV is required to attain current density of 50 mA cm^?2 in comparison with 587 mV for pristine W₁₈O₄₉ NFs. Moreover, the Mo doped W₁₈O₄₉ NFs display relative stability by applying a potential of 503 mV and a current density of 80 mA cm^?2 over 24 h in 0.5 M H₂SO₄ aqueous solution, making them promising in practical applications.     

A high active hydrogen evolution reaction electrocatalyst from ionic liquids-originated cobalt phosphide/carbon nanotubes

Ionic liquid/carbon nanotubes (IL/CNTs) composite was applied as the precursor to prepare CNTs-supported cobalt phosphide via low-temperature phosphidation. CoP_(MBMG)/CNTs, generated from N,N-bis(4-(methoxycarbonyl)benzyl)-N-methyl-d-glucaminium dibromodichlorocobaltate(II) (MBMG)₂-CoCl₂Br₂), exhibits the best catalytic activity toward hydrogen evolution reaction with an onset overpotential of 55 mV, a Tafel slope of 58 mV dec^?1, 95% Faradaic efficiency (FE), current densities of 10 and 20 mA cm^?2 at overpotentials of 135 and 160 mV, and it can maintain the catalytic activity for at least 27 h. FT-IR, Raman spectroscopy, XPS and XRD were utilized to investigate the phosphidation process. All experimental results confirmed that anion from (MBMG)₂-CoCl₂Br₂ can form CoP and glucaminium-based cation can become amorphous carbon after phosphidation to obtain the high HER activity of CoP_(MBMG)/CNTs.     

Hierarchical molybdenum carbide/N-doped carbon as efficient electrocatalyst for hydrogen evolution reaction in alkaline solution

Development of highly-active and noble-metal-free electrocatalysts for hydrogen evolution reaction (HER) is of critical challenge for water splitting, and optimizing the structure and the composition of the relative materials is very necessary to obtain the high-quality catalysts. Herein, a novel molybdenum carbide/N-doped carbon (Mo₂C/NC) hybrid is fabricated by using the hierarchical polyaniline tube network as a carbon source and a reactive template, and the as-fabricated Mo₂C/NC hybrid possesses a uniform hierarchical tube structure. The coupling of the ultrafine Mo₂C nanoparticles and the N-doped carbon substrate provides the abundant active sites and accelerates the charge transfer process. The final Mo₂C/NC catalyst gives the excellent catalytic activity for HER in alkaline condition, which shows a lower overpotential of 142 mV at 10 mA cm^?2 and a small Tafel slope of 61 mV decade^?1 in 1 M KOH.     

Improving the electrocatalytic property of CoP for hydrogen evolution by constructing porous ternary CeO2-CoP-C hybrid nanostructure via ionic exchange of MOF

Developing cheaper but efficient electrocatalysts toward hydrogen evolution reaction (HER) are highly desirable for the sustainable energy conversion techniques. The nanostructured CoP has been proved to be one of the most efficient non-noble metal HER catalyst. However, to further improve their performance in hydrogen evolution reaction (HER) is still a challenging task. In the present work, we prepare the nanohybrid CeO₂-CoP-C catalyst with high porosity through a co-ionic-exchange with Co and Ce ions using the metal-organic frameworks (MOFs) as template followed with a low-temperature phosphorization route. The high porosity of the catalysts is conductive to the diffusion and mass transfer of the reactants on the catalyst surface. Meanwhile, the doping of rare earth (RE) element modulates the electronic structure of the CoP nanoparticles, and the carbon skeleton left over from the annealed MOF is beneficial to the electronic conduction in the catalyst. Electrochemical tests showed that the ternary CeO₂-CoP-C/CC hybrid nanostructure presented overpotential of 71 mV at 10 mV cm^?2 (η₁₀), which is much higher than that of the binary CoP-C/CC catalysts (i.e., 132 mV). In addition, the ternary catalyst also presented a superior long-term durability in an acidic electrolyte. This work opens up a potential strategy for designing more efficient CoP-based catalysts toward electrochemical water splitting.     

M (Co,Ni), N and S tridoped carbon nanoplates as multifunctional catalysts for rechargeable Zn-air batteries and water electrolyzers

Exploration of multifunctional non-precious metal catalysts towards oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is very important for many clean energy technologies. Here, two trifunctional catalysts based on M (Co, Ni), N and S tridoped carbon nanoplates (Co/N/S-CNPs and Ni/N/S-CNPs) are reported. Due to the relatively higher catalytic site content, graphitization degree and smaller charge-transfer resistance, the Co/N/S-CNPs catalyst shows higher activity and stability for ORR (onset potential of 0.99 V and half-wave potential of 0.87 V vs. RHE (reversible hydrogen electrode)), OER (overpotential at 10 mA cm^?2 of 0.37 V) and HER than the Ni/N/S-CNPs catalyst. Furthermore, when constructed with the Co/N/S-CNPs and commercial 20 wt% Pt/C + Ir/C cathodes, respectively, Zn-air battery (ZnAB) based on the Co/N/S-CNPs cathode displays better performance, including a higher power density of 96.0 mW cm^?2 and cycling stability at 5 mA cm^?2. In addition, an alkaline electrolyzer assembled with the Co/N/S-CNPs catalyst as a bifunctional catalyst can reach 10 mA cm^?2 at 1.65 V for overall water splitting and maintain excellent stability even after cycling for 12 h. The present work proves the potential of the Co/N/S-CNPs catalyst for many clean energy devices.     

Defect-rich MoS2 nanosheets vertically grown on graphene-protected Ni foams for high efficient electrocatalytic hydrogen evolution

Defect-rich MoS₂ nanosheets are vertically grown on graphene-protected Ni foam by a facial hydrothermal route. The vertically aligned MoS₂ nanosheets with defects such as cracks, amorphousness and oxygen-incorporated disorders endow these as-synthesized catalysts with rich active sites, high conductivity and good stability. The graphene deposited on Ni foam increases its stability in acid. The optimized catalyst exhibits high activity for hydrogen evolution with a quite low overpotential of 140 mV at 10 mA cm^?2, a small Tafel slope of 42 mV decade^?1, and a large exchange current density of 63 μA/cm², as well as excellent stability. This performance is superior to most of its analogue MoS₂ and many transition metal sulfides. This work will broaden the vision to improve the activity of self-supported electrocatalysts by carefully designing the anchored catalysts.     

Phosphorus-doped nickel sulfides/nickel foam as electrode materials for electrocatalytic water splitting

Hydrogen production from electrocatalytic water splitting is viewed as one of the most promising methods to generate the clean energy. In this work, we successfully prepared an electrode material by growing phosphorus-doped Ni₃S₂ (PNi₃S₂) on nickel foam substrate (NF) under hydrothermal conditions. The phosphorus-doping has an obvious effect on the morphology of Ni₃S₂ on the surface of the nickel foam, which probably results in more active sites, higher electrical conductivity and faster mass transfer. The resulting electrode material displays excellent electrocatalytic activities and stability towards both OER (oxygen evolution reaction) and HER (hydrogen evolution reaction). A relatively low overpotential of 306 mV is required to reach the current density of 100 mA cm^?2 for OER and 137 mV at 10 mA cm^?2 for HER in 1 M KOH solution. When PNi₃S₂/NF was used in an electrolyzer for full water splitting, it can generate a current density of 10 mA cm^?2 at 1.47 V with excellent stability for more than 20 h.     

One-step synthesis of amorphous Ni–Fe–P alloy as bifunctional electrocatalyst for overall water splitting in alkaline medium

Design of inexpensive and highly efficient bifunctional electrocatalyst is paramount for overall water splitting. In this study, amorphous Ni–Fe–P alloy was successfully synthesized by one-step direct-current electrodeposition method. The performance of Ni–Fe–P alloy as a bifunctional electrocatalyst toward both hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) was evaluated in 30 wt% KOH solution. It was found that Ni–Fe–P alloy exhibits excellent HER and OER performances, which delivers a current density of 10 mA cm^?2 at overpotential of ～335 mV for HER and ～309 mV for OER with Tafel slopes of 63.7 and 79.4 mV dec^?1, respectively. Moreover, the electrolyzer only needs a cell voltage of ～1.62 V to achieve 10 mA cm^?2 for overall water splitting. The excellent electrocatalytic performance of Ni–Fe–P alloy is attributed to its electrochemically active constituents, amorphous structure, and the conductive Cu Foil.     

Cobalt-molybdenum carbide@graphitic carbon nanocomposites: Metallic cobalt promotes the electrochemical hydrogen evolution reaction

In this work, a series of metallic cobalt-molybdenum carbide@graphitic carbon (CoMo(x:y)-T@GC) nanocomposites for the electrochemical hydrogen evolution reaction (HER) were synthesized by a sol-gel method. In the as-prepared nanocomposites, β-Mo₂C and metallic Co coexisted and were encapsulated by graphitic carbon. The presence of metallic Co effectively enhanced the crystallinity of β-Mo₂C, charge transfer efficiency and electrochemical active surface area (ECSA), thus resulting in the improved HER catalytic activities of the CoMo(x:y)-T@GC nanocomposites. The optimized electrocatalyst CoMo(0.5:0.5)-800@GC required the lowest overpotential of ～165 mV to deliver a current density of 10 mA cm^?2 in 0.1 M KOH, which was at the forefront compared with recently reported Mo₂C-based electrocatalysts.     

Novel strongly coupled tungsten-carbon-nitrogen complex for efficient hydrogen evolution reaction

Alternatives to noble metal based electrocatalysts are vitally necessary to produce hydrogen from water at low overpotentials. Earlier research on tungsten based electrocatalyst has been mainly concentrated towards tungsten carbide (WC) and tungsten nitride (WN) as the potential electrocatalysts for hydrogen evolution reaction (HER), whereas tungsten carbide (W₂C) has been least focused upon. Herein, we report a highly active novel strongly coupled tungsten-carbon-nitrogen complex (W₂C-NC-WN complex) prepared by in situ carbonization method. This W₂C-NC-WN complex exhibits a remarkable electrochemical performance for HER with a small onset potential of 33 mV vs. RHE and requires an overpotential (η) of 145 mV vs. RHE to render ?10 mA cm^?2 current density. The Tafel analysis demonstrates a slope of 96 mV dec^?1 which is much better than WN (109.6 mV dec^?1) and WC (142.4 mV dec^?1). The strong coupling of W₂C and WN within N-doped carbon (NC) framework brings about a significant enhancement in HER kinetics and faster electron transport due to the remarkable reduction in charge transfer resistance. The facile synthetic approach reported here, provides a powerful tool for the structurally controlled modification of the catalyst while simultaneously introducing active species.     

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.     

Ni–MoS2 composite coatings as efficient hydrogen evolution reaction catalysts in alkaline solution

It remains an important project for the development of water splitting electrolyze to design and synthesis of more efficient non-noble metal catalyst. In this work, a structured Ni–MoS₂ composite coating has been synthesized under supergravity fields with nickel sulphamate bath containing suspended MoS₂ submicro-flakes. X-ray diffraction patterns indicate that the MoS₂ submicro-flakes have been successfully incorporated into the Ni matrix. Additionally, SEM shows that the prepared Ni–MoS₂ composite coatings display finer grain size than the pure Ni coatings, which can increase the electrochemistry surface area and the active site of hydrogen evolution reaction. Therefore, due to the synergistic effect of molybdenum disulfide and nickel, the Ni–MoS₂ composite coatings are directly used as binder-free electrode, which exhibits outstanding electrocatalytic activity for HER in 1.0 M NaOH solution at room temperature. The Ni–MoS₂ composite coatings demonstrated an outstanding performance toward the electrocatalytic hydrogen production with low overpotential (100 mA cm^?2 at η = 207 mV), a Tafel slope as small as 65 mV dec^?1, and stable cycling performance (1200 cycles). The preeminent HER performance of this catalyst suggests that it may hold great promise for practical applications.     

MoS2 supported on MOF-derived carbon with core-shell structure as efficient electrocatalysts for hydrogen evolution reaction

In this work, the porous carbon polyhedra were firstly obtained by carbonizing the zeolite imidazole framework (ZIF-8). Then the carbon polyhedra and precursors of MoS₂ were successfully combined by a hydrothermal reaction, forming the C-MoS₂ composites with different carbon contents. The well-tuned C-MoS₂ sample possesses a core-shell morphology, in which the carbon substrate is well decorated by vertically aligned MoS₂ ultrathin nanosheets. The resulting composites can be used as electrocatalysts of hydrogen evolution reaction (HER), displaying significantly superior activities to pure MoS₂ and carbon. It's found that the carbon content largely affects the architectures and HER behaviors of catalysts. In particular, the optimized catalyst yields the best catalytic activity with the lowest onset potential (35 mV), smallest Tafel slope (53 mv dec^?1), lowest overpotential (200 mV at 10 mA cm^?2), as well as extraordinary long-term stability in H₂SO₄. The enhanced HER activity can be attributed to the unique core-shell structure, where abundant active edge sites of MoS₂ are exposed and the underlying carbon substrate effectively improves the conductivity of the electrode.     

Ultrafine Co6Mo6C nanocrystals on reduced graphene oxide as efficient and highly stable electrocatalyst for hydrogen generation

Up to now, it is still a great challenge to develop active, durable and low-cost non-precious metal catalysts toward hydrogen evolution reaction (HER). In this paper, we synthesized ultrafine Co₆Mo₆C nanocrystals on reduced graphene oxide (RGO) support (Co₆Mo₆C/RGO). The Co₆Mo₆C/RGO shows Pt-like HER performance, which exhibits almost zero onset overpotential, and very small overpotential of 64 mV at 10 mA cm^?2. In addition, the Co₆Mo₆C/RGO has a very small Tafel slope of 44 mV dec^?1 and a high exchange current density of 0.402 mA cm^?2, suggesting fast reaction kinetics. Furthermore, the Co₆Mo₆C/RGO demonstrates superior durability in acid electrolyte. The distinguished HER performance makes Co₆Mo₆C/RGO the promising candidate as non-precious metal catalyst for HER in acid electrolyte.     

Synthesis of lawn-like NiS2 nanowires on carbon fiber paper as bifunctional electrode for water splitting

a low-cost electrode with lawn-like NiS₂ nanowire arrays on flexible carbon fiber paper was synthesized, for the first time, via sulfurization of Ni₂(CO₃)(OH)₂ precursor. And the performance of this electrode as a bifunctional electrocatalyst toward both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) was evaluated. It shows that NiS₂ NWs/CFP requires small overpotentials of 165 mV for HER and 246 mV for OER, respectively, to deliver the current density of 10 mA cm^?2 in 1.0 M KOH. The corresponding symmetric two-electrode alkaline water electrolyzer only needs a cell voltage of 1.59 V to afford 10 mA cm^?2 water-splitting current density.     

Syntheses of nickel sulfides from 1,2-bis(diphenylphosphino)ethane nickel(II)dithiolates and their application in the oxygen evolution reaction

In this work, four heteroleptic Ni(II)dppe dithiolates complexes, [Ni(NED)(dppe)] (Ni-NED), [Ni(ecda)(dppe)] (Ni-ecda), [Ni(i-mnt)(dppe)] (Ni-i-mnt) and [Ni(cdc)(dppe)] (Ni-cdc) (dppe = 1,2-bis(diphenylphosphino)ethane; NED = 1-nitroethylene-2,2-dithiolate; ecda = 1-ethoxycarbonyl-1-cyanoethyelene-2,2-dithiolate; i-mnt = 1,1-dicyanoethylene-2,2-dithiolate and cdc = cyanodithioimidocarbonate), have been synthesized and characterized by analytical and spectroscopic techniques (Elemental analysis, vibrational, electronic absorption and multinuclear NMR spectroscopy). Structural characterization of all the four complexes by single crystal X-ray diffraction study suggests distortion in regular square planar geometry at Ni(II) center by coordination with two phosphorus of the dppe and two sulfur of the dithiolate ligands, respectively. The decomposition of all four complexes have been done to produce nickel sulfides and the resulting nickel sulfides have been utilized for electrocatalytic oxygen evolution reaction (OER). The nickel sulfide obtained by decomposing Ni-cdc shows best activity with overpotential η = 222 mV at j = 10 mA cm^?2 and a Tafel slope of 44.2 mV dec^?1 while other catalysts shows η > 470 mV at j = 5 mA cm^?2 and η > 600 mV at j = 10 mA cm^?2 at loading of 1.3 mg cm^?2.     

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.     

Nickel selenide nanostructures as an electrocatalyst for hydrogen evolution reaction

Electrochemical water splitting has gained momentum for the development of alternative energy sources. Herein, we report the synthesis of two different nickel selenide nanostructures of different morphology and composition employing hydrothermal method. NiSe₂ nanosheets were obtained by the anion-exchange reaction of Ni(OH)₂ with Se ions for 15 h. On the other hand, NiSe nanoflakes were synthesized by the direct selenization of nickel surface with the reaction time of 2 h. Tested as an electrocatalyst for hydrogen evolution reaction, NiSe₂ nanosheets and NiSe nanoflakes can afford a geometric current density of 10 mA cm^?2 at an overpotential of 198 mV and 217 mV respectively. The measured Tafel slope values of NiSe nanoflakes are 28.6 mV dec^?1, which is three times lower as compared with NiSe₂ nanosheets (72.1 mV dec^?1). These results indicates the HER kinetics of NiSe nanoflakes are at par with the state-of-the-art Pt/C catalyst and also complimented with the short synthesis time of 2 h. Further, both nickel selenides exhibit ultra-long term stability for 30 h as evident from constant current chronopotentiometry and electrochemical impedance spectroscopy results.