In-situ grown of Ni2P nanoparticles on 2D black phosphorus as a novel hybrid catalyst for hydrogen evolution

Nickel phosphide-based nanomaterials have been acted as efficient catalysts for the hydrogen evolution reaction (HER), however, the design of novel and high performance HER catalyst is still a challenge. Herein, we report a novel 2D material black phosphorus (BP) as support for constructing Ni₂P-based hybrid catalyst by a one-pot thermal decomposition approach. TEM results indicated that the monodispersed Ni₂P nanoparticles with small size and good dispersion supported on the surface of layered BP, which implied that more catalytic active sites may be exposed for HER. The as-synthesized Ni₂P/BP hybrid exhibits high HER electrocatalytic performance with low onset overpotential (70 mV), small Tafel slope (81 mV dec^?1), large double-layer capacitance (1.24 mF cm^?2), high conductivity and good stability, which can be assigned to the strong synergistic effect between Ni₂P and BP. Therefore, BP may be a suitable support for constructing excellent catalysts in electrocatalysis.     

Highly efficient and stable bifunctional electrocatalyst for water splitting on Fe–Co3O4/carbon nanotubes

Replacement of precious platinum (Pt) or ruthenium oxide (RuO₂) catalysts with efficient, cheap and durable electrocatalysts from earth-abundant elements bifunctional alternatives would be significantly beneficial for key renewable energy technologies including overall water splitting and hydrogen fuel cells. Despite tremendous efforts, developing bifunctional catalysts with high activity at low cost still remain a great challenge. Here, we report a nanomaterial consisting of core-shell-shaped Fe–Co₃O₄ grown on carbon nanotubes (Fe–Co₃O₄/CNTs) and employed as a bifunctional catalyst for the simultaneous electrocatalysts on oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The Fe–Co₃O₄/CNTs electrocatalyst outperforms the commercial RuO₂ catalyst in activity and stability for OER and approaches the performance of Pt/C for HER. Particularly, it shows superior electrocatalytic activity with lowering overpotentials of 120 mV at 10 mA cm^?2 for HER and of 300 mV at 10 mA cm^?2 for OER in 1 M KOH solution. The superior catalytic activity arises from unique core-shell structure of Fe–Co₃O₄ and the synergetic chemical coupling effects between Fe–Co₃O₄ and CNTs.     

Cobalt based nanostructured alloys: Versatile high performance robust hydrogen evolution reaction electro-catalysts for electrolytic and photo-electrochemical water splitting

Engineering reduced noble metal containing electro-catalysts exhibiting superior electrochemical performance is important for efficient and economic production of hydrogen from electrolytic and photoelectrochemical (PEC) water splitting reactions. In this study, nanostructured Co–Ir solid solution alloys, Co_1?x(Ir_x) (x = 0.2, 0.3, 0.4) have been studied as electro-catalysts for hydrogen evolution reaction (HER). Co_1?x(Ir_x) (x = 0.3, 0.4) exhibit similar onset over-potential to Pt/C and lower over-potential required for Co_1?x(Ir_x) (x = 0.3, 0.4) than Pt/C in acidic, neutral as well as basic media, suggesting excellent electrochemical activity of Co–Ir alloys, further studied using theoretical first principles density functional theory calculations. Co_1?x(Ir_x) exhibit excellent electrochemical stability in acidic media similar to that of Pt/C. The applied bias photon-to-current efficiency obtained using Co_1?x(Ir_x) (x = 0.3, 0.4) electro-catalysts and (Sn_0.95Nb_0.05)O₂:N-600 NTs as photoanode in H-type cell is ～5.74% and ～7.92%, respectively which is ～40% and ～93% higher than Pt/C (～4.1%) indicating considerable promise of the system.     

Highly efficient electrocatalytic hydrogen production via MoSx/3D-graphene as hybrid electrode

Molybdenum sulfide (MoS_x) has recently emerged as a promising catalyst for the hydrogen evolution reaction (HER) in water splitting that may replace the noble metal, such as platinum, as a cost-effective and high catalytic materials. It has been reported that two-dimensional structured MoS_x exhibit significant amount of exposed S-edge, which can be an active electrocatalytic catalyst for hydrogen production. However, the current reports mainly focusing on the planar electrode, where the catalyst utilization and the number of active sites are limited due to the lower exposed specific surface area (SSA) of supporting electrodes. In this work, we utilize the freeze-drying method to produce a porous three-dimensional (3D) structure assembled by graphene flakes. The as-prepared 3D graphene scaffold shows high surface area, high porosity while low density, which makes it as an ideal conductive electrode for supporting of MoS_x catalysts. Moreover, it was found out that the crystallinity of MoS_x, controlled by thermolysis temperature of thiosalts precursor ((NH₄)₂MoS₄), shows significantly influence the performance of HER. The optimized annealing temperature for the designed hybrid electrodes (MoS_x/3D-graphene) was found to create a lot of active sites, which facilitate the electrocatalytic performance for water splitting (overpotential of 163 mV @10 mA/cm² and a Tafel slope of 41 mV/dec). The study provides a potential material, which could pave the way for future applications of hydrogen energy.     

Nanoscale engineering MoP/Fe2P/RGO toward efficient electrocatalyst for hydrogen evolution reaction

The preparation of hydrogen evolution reaction (HER) electrocatalyst with high catalytic performance is a huge challenge. In this work, we develop a MoP/Fe₂P/RGO composite as a electrocatalyst for HER. The MoP/Fe₂P/RGO exhibits excellent electrocatalytic performance with a Tafel slope and an onset overpotential of 51 mV/dec and 105 mV, respectively. To drive 10 mA/cm², it only requires a small over-potential of 156 mV. The high electrocatalytic HER activity is mainly due to the synergistic effect of MoP and Fe₂P. In addition, the introduction of RGO not only prevents particle aggregation and coalescence during high temperature phosphating, but also improves the conductivity of the catalyst.     

Spherical Co/Co9S8 as electrocatalyst for hydrogen production from alkaline solution and alkaline seawater

Cobalt-based sulfide catalysts are considered as potential materials for electrocatalytic hydrogen production from seawater. Here, we have successfully prepared a Co/Co₉S₈ electrocatalyst with hollow spherical structure. As-prepared material exhibited excellent electrocatalytic activity in hydrogen evolution reaction (HER) in alkaline seawater. The overpotentials for Co/Co₉S₈ in alkaline seawater were measured as low as 136.2 mV, when reached a current density of 10 mA cm^{− 2}. It also had good stability and could be maintained for 24 h in 1.0 M KOH and alkaline seawater. The results of SEM and TEM confirmed that the catalyst had excellent reaction structure. Due to the hollow structure, Co/Co₉S₈ showed remarkable catalytic performance for HER. The construction method of Co/Co₉S₈ hollow structure is an effective strategy to improve the performance of HER for seawater splitting.     

Trimetallic NiFeCo selenides nanoparticles supported on carbon fiber cloth as efficient electrocatalyst for oxygen evolution reaction

Trimetallic NiFeCo selenides (NiFeCoSe_x) anchored on carbon fiber cloth (CFC) as efficient electrocatalyst for oxygen evolution reaction (OER) in alkaline medium have been synthesized via a facile two-step method. Firstly, trimetallic NiFeCo (oxy) hydroxides have been electrodeposited on CFC support (NiFeCo/CFC). Secondly, a solvothermal selenization process has been used to convert NiFeCo/CFC into NiFeCoSe_x/CFC using N, N-dimethylformamide (DMF) as solvent. The composition and homogeneous distribution of NiFeCoSe_x/CFC nanoparticles are determined by XRD, XPS, SEM elemental mapping and EDX images. Furthermore, SEM images reveal that NiFeCoSe_x/CFC has volcano-shaped morphology with rough surface and homogenously distributed on the surface of CFC, which may provide more active sites for OER. The electrochemical measurements show that trimetallic NiFeCoSe_x/CFC possesses the better electrocatalytic activity with the lower overpotential (150 mV at 10 mA cm^?2), Tafel slope (85 mV dec^?1), larger double-layer capacitance (200 mF cm^?2) and long-term stability than unary or binary metal selenides. The enhanced activity of NiFeCoSe_x/CFC may be attributed to the trimetallic NiFeCo selenides and selenides-CFC synergistic interaction. It may offer a promising way to design transition multimetallic selenides supported on conductive support as electrocatalysts for OER.     

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.     

Efficient hydrogen evolution electrocatalysts from LixMoS2 nanoparticles on three-dimensional substrate

Molybdenum disulfide (MoS₂), as a promising catalyst, has been widely investigated for hydrogen evolution reaction (HER). But the low density and poor reactivity of active sites, poor electrical transport, and inefficient electrical contact to the catalyst, leads to the modest performance. In this work, we demonstrate an effective route to overcome those issues by decorating the conductive Li_xMoS₂ nanoparticles on the three-dimensional carbon fiber paper (CFP) through combining hydrothermal method and lithium intercalation. Thus, the dense Li_xMoS₂ nanoparticles of the surface can provide the large number of exposed active sites, the highly-conductive Li_xMoS₂ nanoparticles and CFP substrate can facilitate the transfer of electron not only between the Li_xMoS₂ nanoparticles and CFP, but also between the whole sample and current collector, and the porous networked structure can enable the diffusion and penetration of electrolyte. Prompted by those advantage, the as-prepared samples exhibit outstanding HER catalytic activity with the small Tafel slope of 62 mv dec^?1 and the low overpotential of ?115.6 mV vs RHE at an electrocatalytic current density of 10 mA cm^?2. Chronoamperometric current test for 10 h confirms the long-term stability of the catalyst.     

Mixed-metal MOF-derived Co-doped Ni3C/Ni NPs embedded in carbon matrix as an efficient electrocatalyst for oxygen evolution reaction

The exploration of electrocatalysts with high oxygen evolution reaction (OER) activity is highly desirable and remains a significant challenge. Transition metal carbides (TMCs) have been investigated as remarkable hydrogen evolution reaction (HER) electrocatalysts but few used as oxygen evolution reaction (OER) electrocatalysts. Herein, a Co doped Ni₃C/Ni uniformly dispersed in a graphitic carbon matrix was prepared by pyrolysis of a metal organic framework (Co/Ni-MOF) under a flow of Ar/H₂ at 350 °C, and Ni₃C/Ni@C was also prepared for comparison. The various characterization techniques confirmed the successful preparation of the heteroatom doped TMCs-based catalysts by pyrolysis of MOFs. Co doped Ni₃C/Ni@C exhibited superior electrocatalytic properties for OER. For example, Co–Ni₃C/Ni@C depicts a lower overpotential and smaller Tafel slope than Ni₃C/Ni@C and IrO₂ during the OER in 1 M KOH solution, additionally, it shows a higher active surface area than Ni₃C/Ni@C. The outstanding electrocatalytic performance of Co-doped Ni₃C/Ni@C in the OER was mainly ascribed to the synergistic effect of the Co and Ni₃C/Ni active sites.     

Partial phosphorization of porous Co–Ni–B for efficient hydrogen evolution electrocatalysis

Design of cost-effective and high-efficient electrocatalysts for hydrogen evolution reaction (HER) is of vital significance for the current renewable energy devices — fuel cells. Herein, we report a facile strategy to prepare partial phosphorization of Co–Ni–B material with porous structure via a water-bath boronizing and subsequent phosphorization process at moderate temperature. The optimal atomic proportion of Co to Ni is investigated via physical and electrochemical characterization. As a result, Co₉–Ni₁–B–P exhibits the best HER activity, which require an lower overpotential of ~192 mV to deliver a current density value of 10 mA cm⁻² and a smaller Tafel slope of 94 mV dec⁻¹ in alkaline media, relative to P-free Co–Ni–B catalysts, Co₉–Ni₁–B–P with other Co: Ni proportion and mono metallic borides The excellent electrocatalytic performance of Co₉–Ni₁–B–P is mainly ascribed to the three-dimensional (3D) porous structure and the coordinate functionalization between the borides and phosphides. This work provides a promising strategy for the exploration of quaternary composites as efficient and cost-effective electrocatalysts for HER.     

One-step electrodeposition of cauliflower-like CozNiySx@polypyrrole electrocatalysts on carbon fiber paper for hydrogen evolution reaction

Transition-metal chalcogenides as the promising alternatives to noble-metal-based electrocatalysts for hydrogen evolution reaction (HER) with high activity and durability in water splitting have attracted extensive attention in recent years. Herein, Co_zNi_yS_x@PPy composites with three-dimensional (3D) cauliflower-like were firstly prepared on carbon fiber paper (CFP) via a simple and efficient electrochemical reduction of elemental sulfur in the precursor of S@PPy composite coated on CFP to react with Co and Ni ions in the electrolyte. The optimum electrode, i.e., Co_zNi_yS_x@PPy/CFP-6 (A-6) prepared by using an electrolyte with a Co/Ni molar ratio of 0/6, showed excellent catalytic activity (with an overpotential of 185 mV@10 mA cm⁻² and a small Tafel slope of 78.13 mV dec⁻¹) as well as long-term stability (at least 100 h) in 1 M KOH solutions. This work provides a novel way to fabricate effective and non-noble-metal electrodes for HER in water splitting.     

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.     

Facile synthesis of NiS2 nanowires and its efficient electrocatalytic performance for hydrogen evolution reaction

Recently, the first-row transition metal dichalcogenides MX₂ (M = Fe, Co, Ni; X = S, Se) have been widely reported as promising catalysts for hydrogen evolution reaction (HER) because of its excellent catalytic activity and earth-abundance. The rational nanostructure designs have been proved as an effective way to improve their catalytic performance. However, the reported one dimension (1D) NiS₂ nanowires for HER suffer from a large Tafel slope. Here, we report a facile synthesis of 1D NiS₂ nanowires and its high efficient catalytic activity in HER. This nanowire structure with large surface area and active sites enables highly efficient electrocatalytic performance in HER with a much smaller Tafel slope (83.5 mV/dec) compared to that of bulk NiS₂ (136 mV/dec) as well as long-term stability. Our work builds up a structure–performance relationship and enriches the synthetic strategy to other efficient catalysts such as first-row transition metal dichalcogenides or transition metal phosphide.     

Controlled synthesis of NiCoM (M=P,S, Se,O)–Ni3S2–MoS2 hybrid material as environmentally friendly water splitting catalyst

The study of high efficiency and low cost catalysts is of great significance to the overall development of electrochemistry. In this paper, NiCoM (M = P, S, Se, O)–Ni₃S₂–MoS₂ hybrid material was prepared by hydrothermal, calcination and hydrothermal three-step reaction method, and its hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline environment were studied and compared. The experimental results showed that at 10 mA cm^?2, the overpotential of NiCoP–Ni₃S₂–MoS₂ was only 140 mV for HER, while the overpotential of NiCoSe–Ni₃S₂–MoS₂ was only 160 mV for OER. Compared with other catalysts, the activity of NiCoP–Ni₃S₂–MoS₂ and NiCoSe–Ni₃S₂–MoS₂ was higher, and the chemical reagents needed for preparation were cheap and low cost. What is noteworthy is that the morphology of NiCoP–Ni₃S₂–MoS₂ material change after long time stability test for hydrogen evolution reaction, the change makes the performance of the samples toward a better direction. A series of characterization found that the surface of the NiCoP–Ni₃S₂–MoS₂ samples increased more holes and more active site, and did not produce new material after other characterization. Density functional theory calculation shows that the presence of this MoS₂ material accelerates the kinetics of hydrogen production and this Co₂P material enhances the conductivity of the material. Their synergistic effect makes the NiCoP–Ni₃S₂–MoS₂ catalyst exhibit enhanced hydrogen production activity. The bramble structure of NiCoSe–Ni₃S₂–MoS₂ allows the sample to have more active sites and higher electrocatalytic activity during the OER process. This experiment provides new insights into the preparation of robust water splitting catalysts by simple methods.     

Ni and N co-doped MoCx as efficient electrocatalysts for hydrogen evolution reaction at all-pH values

To achieve sustainable production of H₂ fuel through water splitting, noble-metal-free catalysts have been extensively studied for hydrogen evolution reaction (HER), especially molybdenum-based catalysts. Herein, we report the Ni, N-codoped MoC_x (Ni–N–MoC_x) nanoparticles synthesized from NiMoO₄ precursor by oily-solvent-assisted strategy, following the calcination with dicyandiamide. As-obtained Ni–N–MoC_x in different magnified SEM images shows grainy structure, MoC_x nanoparticles uniformly disperse in carbon substrate. The obtained electrocatalysts can also efficiently electrocatalytic HER in a wide pH value. Ni–N–MoC_x shows an onset potential of ?74 mV, an overpotential of 163 mV to reach a current density of 10 mA/cm² in acid media, an onset potential of ?37 mV and overpotential of 124 mV to reach 10 mA/cm² in alkaline media. The present study provides some guidelines for preparing the uniformly doped electrocatalysts from multiple compounds with devolatilization characteristics.     

Hollow ZnxCo1-xSe2 microcubes derived from Metal–Organic framework as efficient bifunctional electrocatalysts for hydrogen evolution and oxygen evolution reactions

Herein, we designed a simple and universal method to prepare cobalt-based bimetallic Zn_xCo_1-x-MOFs precursors, which were used as templates to synthesize effective bifunctional electrocatalyst hollow porous Zn_xCo_1-xSe₂ microcubes by one-step hydrothermal method. The cubic morphology of the Zn_xCo_1-x-MOFs precursors was well inherited. Particularly, the Zn_0.1Co_0.9Se₂ exhibited superior HER and OER performance in acidic solution and alkaline solution, respectively. Benefiting from the hollow porous structure, the synergistic effect of Zn–Co–Se and the incorporation of a small number of zinc atoms.

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In situ growth of MoS2 on carbon nanofibers with enhanced electrochemical catalytic activity for the hydrogen evolution

Developing an effective and facile method to achieve mass production of MoS₂ nanostructures with abundant of edges may be the feasible way to meet the increasing demand for hydrogen evolution electrocatalysts. We developed a facile glucose-assisted hydrothermal method to in-situ grow MoS₂ nanosheets on the commercial carbon nanofibers (CNFs). The controlled growth of MoS₂ on CNFs (MoS₂@CNFs) is leveraged to reveal mass ratio- and structure-dependent catalytic activity in the hydrogen evolution reaction (HER). Due to the unique shell structure, abundant edges of the MoS₂ layer are exposed as active site, as well as the underlying CNFs effectively improves the conductivity, the resulting MoS₂@CNFs hybrid exhibited high electrocatalytic activity in HER. The catalyst demonstrated the lowest overpotential of 52 mV, the highest current density of 101.49 mA cm^?2 at ～200 mV overpotential and the smallest Tafel slope of 49 mV/decade, suggesting the Volmer–Heyrovsky mechanism for the MoS₂-catalyzed HER.     

Preparation of mesoporous Ni2P nanobelts with high performance for electrocatalytic hydrogen evolution and supercapacitor

The development of bifunctional electrochemically-active materials for both hydrogen evolution reaction (HER) and supercapacitors enables the possibility to integrate energy storage and production into one single system. Here, we report a novel bifunctional mesoporous Ni₂P nanobelt-like architecture prepared via the hydrothermal synthesis of Ni(SO₄)_0.3(OH)_1.4 nanobelt precursor and subsequent low temperature phosphorization process under Ar atmosphere. Composed of numerous cross-linked Ni₂P nanoparticles, the as-obtained Ni₂P nanobelts exhibit a two dimensional leaf-like morphology, allowing remarkable enhancement of mesoporosity as well as active surface area. The HER electrocatalytic test in acid medium show a current density of 16 mA cm^?2 at an overpotential of 187 mV, Tafel slope of 62 mV dec^?1 and long-term durability. Investigation of this Ni₂P nanobelts as supercapacitor materials in 2M KOH electrolyte display a high specific capacity ranging from 1074 F g^?1 at 0.625 A g^?1 to 554 F g^?1 at 25 A g^?1, and notable cycling life with 86.7% retention after 3000 cycles at 10 A g^?1. With the simplicity of the synthetic routine and the outstanding performance as both HER catalysts and supercapacitors, the Ni₂P nanobelts provide promising potential for energy devices.     

Application of Co3O4-based materials in electrocatalytic hydrogen evolution reaction: A review

Environmental pollution and energy shortage make the development of clean energy more and more urgent. As a kind of clean renewable energy, hydrogen have attracted great attentions in recent years. Recently, Co₃O₄-based materials have emerged as promising candidates for electrocatalytic hydrogen evolution reaction (HER), due to their attractive electrocatalytic activity, low cost as well as the electrochemical durability, which make it attract widely attentions. In this review, we summarize the application of Co₃O₄-based materials in electrocatalytic HER, including pure Co₃O₄, the doped Co₃O₄ and the Co₃O₄-based composite materials. Furthermore, the strategies to enhance their electrocatalytic performance are summarized and discussed, such as morphological engineering, doping, as well as compositing with other materials. Finally, the limitation and challenges of Co₃O₄-based materials for HER, as well as their prospects for future research, are proposed. We believe that this review will be helpful for scientists to seek promising HER electrocatalytic materials.