Highly efficient and durable phosphine reduced iron-doped tungsten oxide/reduced graphene oxide nanocomposites for the hydrogen evolution reaction

The design and development of inexpensive and highly efficient electrocatalysts for hydrogen production from water splitting are highly crucial for green energy and the hydrogen economy. Herein, we report phosphine reduced an iron-doped tungsten oxide nanoplate/reduced graphene oxide nanocomposite (Fe-WOxP/rGO) as an excellent electrocatalyst for the hydrogen evolution reaction. This electrocatalyst was synthesized using a hydrothermal method, followed by reduction with phosphine (PH₃), which was generated from sodium hypophosphite. The catalyst onset potential, Tafel slope, and stability were investigated. Accordingly, Fe-WOxP/rGO exhibited impressively high electrocatalytic activity with a low overpotential of 54.60 mV, which is required to achieve a current density of 10 mAcm^?2. The Tafel slope of 41.99 mV dec^?1and the linear sweep voltammetry curve is almost the same as 2000 cycles and electrolysis under static overpotential (54.60 mV) is remain for more than 24 h in 0.5 M H₂SO₄. The catalytic activity and conductivity of Fe-WOxP/rGO were higher than WO_XP, Fe-WOxP and WOxP/rGO. Such an outstanding performance of the Fe-WOxP/rGO nanocomposite is attributed to the coupled synergic effect between high oxygen vacancies formation on tungsten oxide in the nanoplate-like structure of Fe-WOxP and rGO nanosheet, making it as an excellent electrocatalyst for hydrogen evolution reaction.     

Porous CoP nanostructure electrocatalyst derived from DUT-58 for hydrogen evolution reaction

The development of efficient, non-precious metal catalysts for preparing hydrogen by water decomposition, which is a perfect alternative for increasingly serious environmental pollution and energy needs. In this work, we report that a porous CoP-350 nanostructure material was prepared using Co-based metal organic frameworks (DUT-58) as the precursor by pyrolysis and low temperature phosphating. The porous CoP-350 nanostructure electrocatalyst in this report exhibits excellent performance with a small Tafel slope of 64 mV dec^?1, long-term durability and an overpotential of 126 mV at current density 10 mA cm^?2 in 0.5 M H₂SO₄ for the hydrogen evolution reaction (HER). All in all, this work provides an approach to synthesize porous CoP nanostructure as the transition metal phosphides catalyst.     

Three-dimensional structure of WS2/graphene/Ni as a binder-free electrocatalytic electrode for highly effective and stable hydrogen evolution reaction

Tungsten disulfide (WS₂) has attracted much attention as the promising electrocatalyst for hydrogen evolution reaction (HER). Herein, the three-dimensional (3D) structure electrode composed of WS₂ and graphene/Ni foam has been demonstrated as the binder-free electrode for highly effective and stable HER. The overpotential of 3D WS₂/graphene/Ni is 87 mV at 10 mA cm^?2, and the current density is 119.1 mA cm^?2 at 250 mV overpotential, indicating very high HER activity. Moreover, the current density of 3D WS₂/graphene/Ni at 250 mV only decreases from 119.1 to 110.1 mA cm^?2 even after 3000 cycles, indicating a good stability. The high HER performance of 3D WS₂/graphene/Ni binder-free electrode is superior than mostly previously reported WS₂-based catalysts, which is attributed to the unique graphene-based porous and conductive 3D structure, the high loading of WS₂ catalysts and the robust contact between WS₂ and 3D graphene/Ni backbones. This work is expected to be beneficial to the fundamental understanding of both the electrocatalytic mechanisms and, more significantly, the potential applications in hydrogen economy for WS₂.     

Mass production of Nickel@Carbon nanoparticles attached on single-walled carbon nanotube networks as highly efficient water splitting electrocatalyst

Herein, we develop a direct current arc discharge method which enables large-scale synthesis of nickel@carbon attached single-walled carbon nanotube networks as an electrocatalyst for highly efficient water splitting. Mass amount of Ni@C/SCN (～80 g) could be easily obtained. After optimization, the catalyst exhibits a superior performance of electrochemical water splitting, which allows a current density of 10 mA cm^?2, with an overpotential of only 260 mV for OER and 198 mV for HER. The electrolyzer can achieve a current density of 10 mA cm^?2 at 1.8 V.     

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.     

Large surface and pore structure of mesoporous WS2 and RGO nanosheets with small amount of Pt as a highly efficient electrocatalyst for hydrogen evolution

In this work, mesoporous WS₂ with high surface area was prepared by hard template method. First, a one-step nanocasting generates metal precursor@mesoporous silica SBA-15 composites. A hydrothermal method is subsequently adopted to convert the precursors to sulfides in the confined nanochannels. After etching silica SBA-15, mesoporous layered metal sulfide crystals were obtained as the products. Then, we have put forward a new catalyst based on mesoporous WS_2, RGO nanosheets and Pt nanoparticles as a highly efficient electrocatalyst for hydrogen evolution. The Pt/WG-2 nanostructure electrocatalyst in this report exhibits excellent performance with a small Tafel slope of 47 mV dec^?1, long-term durability and an overpotential of 95 mV in 0.5 M H₂SO₄ for the hydrogen evolution reaction (HER).     

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.     

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.     

Nickel decorated MoO3 single crystal microflakes with multi-site functionality for enhanced hydrogen evolution reaction

Role of hybrid material with metal-oxide interface has been explored by coating 2 nm nickel on α-MoO₃ single crystals for hydrogen evolution reaction (HER). The investigated aspects reveal that α-MoO₃/Ni hybrid exhibits a remarkable performance in HER showing +6 mV onset potential and 37 mV overpotential at 10 mA/cm² current density along with Tafel slope of 47 mV/dec. The single crystalline-stepped CVD-grown MoO₃ microflakes having the advantage of higher hydrogen binding energy of Ni exhibits the enhanced catalytic performance due to strong electronic coupling at the metal-oxide interface and hydrogen spill over effect. Similar hybrid material composed of Cu-MoO₃ does show improvement but not as good as Ni-MoO₃. A decrease of ~36% is observed in the overpotential for Ni-coated MoO₃ compared to pure MoO₃ crystals indicating the positive contribution of Ni-coating. The hybrid Ni-MoO₃ shows the new route to develop alternate transition metal oxide-based hybrid catalyst towards production of hydrogen fuel.     

Nanoengineered Zn-modified Nickel Sulfide (NiS) as a bifunctional electrocatalyst for overall water splitting

Developing an efficient and inexpensive electrocatalyst is of paramount importance for realizing the green hydrogen economy through electrocatalytic water splitting. Here, we demonstrated a facile large-scale, industrially viable binder-free synthesis of Zn-doped NiS electrocatalyst on bare nickel foam (NF) through a hydrothermal technique. The present catalyst, i.e., nickel sulfide (NiS) nanosheets on nickel foam with optimized doping of Zn atom (Zn–NiS-3), displays excellent catalytic efficacy for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). It requires an overpotential of 320 mV for OER at a current density of 50 mA cm⁻² and an overpotential of 208 mV for HER at a current density of 10 mA cm⁻². The water electrolyser device having Zn–NiS-3 electrocatalyst as both cathode and anode show excellent performance, requiring a cell voltage of only 1.71 V to reach a current density of 10 mA cm⁻² in an alkaline media. The density functional theory (DFT) based calculations showed enhanced density of states near Fermi energy after Zn doping in NiS and attributed to the enhanced catalytic activities. Thus, the present study demonstrates that Zn–NiS-3@NF can be coined as a viable electrocatalyst for green hydrogen production.     

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.     

MOF-derived cobalt manganese phosphide as highly efficient electrocatalysts for hydrogen evolution reaction

Hydrogen is considered as a viable alternative to traditional fossil fuels. Hydrogen evolution reaction (HER) by electrochemical water splitting is the most reliable and effective way for the sustainable production of pure hydrogen. The design and synthesis of highly active and stable non-noble-metal-based electrocatalysts is the core of the large-scale application of this technology. Herein, peony petal-like CoMnP/NF nanomaterials growing on nickel foam (NF) are prepared via facile hydrothermal and phosphorization methods. The results showed that CoMnP/NF had excellent HER activity in acidic and alkaline media. In 0.5 M H₂SO₄, CoMnP/NF only needed 66.6 mV overpotential to drive the current density of 10 mA cm^?2, with a Tafel slope of 38.8 mV dec^?1. In addition, a particularly low overpotential of 53.9 mV and Tafel slope of 63 mV dec^?1 are required to achieve the same current density in the 1 M KOH electrolyte. Meanwhile, the electrocatalyst showed good stability after 1000 cyclic voltammetry tests and 12 h I-T tests. In the 1 M KOH electrolyte, the current density of 10 mA cm^?2 achieved with only 1.70 V battery voltage, and the electrocatalyst showed excellent stability. The performance of CoMnP/NF can be attributed to the synergistic effect between Co and Mn atoms and the high electrochemical surface area (ECSA). This study provides a valuable strategy for the synthesis of non-precious metals and high-performance catalytic materials.     

One-pot solvothermal synthesis of Co2P nanoparticles: An efficient HER and OER electrocatalysts

Development of an inexpensive electrocatalyst for hydrogen evolution (HER) and oxygen evolution reactions (OER) receives much traction recently. Herein, we report a facile one-pot ethyleneglycol (EG) mediated solvothermal synthesis of orthorhombic Co₂P with particle size ~20–30 nm as an efficient HER and OER catalysts. Synthesis parameters like various solvents, temperatures, precursors ratios, and reaction time influences the formation of phase pure Co₂P. Investigation of Co₂P as an electrocatalyst for HER in acidic (0.5 M H₂SO₄) and alkaline medium (1.0 M KOH), furnishes low overpotential of 178 mV and 190 mV, respectively to achieve a 10 mA cm^?2 current density with a long term stability and durability. As an OER catalyst in 1.0 M KOH, Co₂P shows an overpotential of 364 mV at 10 mA cm^?2 current density. Investigation of Co₂P NP by XPS analysis after OER stability test under alkaline medium confirms the formation of amorphous cobalt oxyhydroxide (CoOOH) as an intermediate during OER process.     

Flower-like HEA/MoS2/MoP heterostructure based on interface engineering for efficient overall water splitting

The development of cheap, efficient, and active non-noble metal electrocatalysts for total hydrolysis of water (oxygen evolution reaction (OER) and hydrogen evolution reaction (HER)) is of great significance to promote the application of water splitting. Herein, a heterogeneous structured electrode based on FeAlCrMoV high-entropy alloy (HEA) was synthesized as a cost-effective electrocatalyst for hydrogen and oxygen evolution reactions in alkaline media. In combination of the interfacial synergistic effect and the high-entropy coordination environment, flower-like HEA/MoS₂/MoP exhibited the excellent HER and OER electrocatalytic performance. It showed a low overpotential of 230 mV at the current density of 10 mA cm⁻² for OER and 148 mV for HER in alkaline electrolyte, respectively. Furthermore, HEA/MoS₂/MoP as both anode and cathode also exhibited an overpotential of 1.60 V for overall water splitting. This work provides a new strategy for heterogeneous structure construction and overall water splitting based on high-entropy alloys.     

Facile construction of porous and heterostructured molybdenum nitride/carbide nanobelt arrays for large current hydrogen evolution reaction

The development of cost-effective, highly efficient and stable electrocatalysts for alkaline water electrolysis at a large current density has attracted considerable attention. Herein, we reported a one-dimensional (1D) porous Mo₂C/Mo₂N heterostructured electrocatalyst on carbon cloth as robust electrode for large current hydrogen evolution reaction (HER). The MoO₃ nanobelt arrays and urea were used as the metal and non-metal sources to fabricate the electrocatalyst by one-step thermal reaction. Due to the in-situ formed abundant high active interfaces and porous structure, the Mo₂C/Mo₂N electrocatalyst shows enhanced HER activity and kinetics, as exemplified by low overpotentials of 54, 73, and 96 mV at a current density of 10 mA cm^?2 and small Tafel slopes of 48, 59 and 60 mV dec^?1 in alkaline, neutral and acid media, respectively. Furthermore, the optimal Mo₂C/Mo₂N catalyst only requires a low overpotential of 290 mV to reach a large current density of 500 mA cm^?2 in alkaline media, which is superior to commercial Pt/C catalyst (368 mV) and better than those of recently reported Mo-based electrocatalysts. This work paves a facile strategy to construct highly efficient and low-cost electrocatalyst for water splitting, which could be extended to fabricate other heterostructured electrocatalyst for electrocatalysis and energy conversion.     

Porous carbon incorporated β-Mo2C hollow sphere: An efficient electrocatalyst for hydrogen evolution reaction

Hydrogen is undoubtedly considered as the cleanest energy source and hence the urgency for production of H₂ is a concern to the scientific community. The major bottleneck for electrocatalytic hydrogen production is still exists as the reported catalysts, mainly noble metal based, are extremely costly. Thus the fabrication of cheap and noble metal free electrocatalyst for Hydrogen Evolution Reaction (HER) is still seeking. Here, a simplistic method is developed for the synthesis of carbon assimilated molybdenum carbide (β-Mo₂C) hollow sphere which showed effective electrocatalysis for HER. The synthesis of desired β-Mo₂CC hollow sphere is based on high temperature carbothermal reduction (800 °C in 10%-H₂/N₂ atmosphere) of carbon incorporated MoO₂ spheres. The synthesized β-Mo₂C with an optimal carbon loading reaches 10 mA/cm^?2 current density at a low overpotential of 146 mV with a small tafel slope of 90 mV dec^?1 for the electrochemical hydrogen evolution (HER) in 0.5 M H₂SO₄. The improved catalytic performance, long-term stability make β-Mo₂CC hollow sphere an auspicious HER electrocatalyst.     

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.     

Homogeneous core–shell NiCo2S4 nanorods as flexible electrode for overall water splitting

Exploring low-cost and highly efficient Water splitting electrocatalyst has been recognized as one of the most challenging and promising ways. NiCo₂S₄ core-shell nanorods supported on nickel foam (NF) have been fabricated by a facile hydrothermal method. The electrochemical performance of NiCo₂S₄@NiCo₂S₄ for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is studied. NiCo₂S₄@NiCo₂S₄/NF exhibits a significantly improved OER and HER performance with an overpotential of 200 mV at 40 mA/cm² and an overpotential of 190 mV at 10 mA/cm². The combination of low charge-transfer resistance, enhanced interaction and charge transport as well as large electrochemical double-layer capacitance enables superior OER and HER. The NiCo₂S₄@NiCo₂S₄/NF nanorod electrode shows excellent electrocatalytic activity with a low voltage 1.57 V and stability with long hour electrolysis, which is highly satisfactory for a prospective bifunctional electrocatalyst.     

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.     

Synthesis of nest-like porous MnCo–P electrocatalyst by electrodeposition on nickel foam for hydrogen evolution reaction

It is very important to develop hydrogen evolution catalyst with high activity and low cost to solve energy crisis. The abundant non-precious metals and phosphides have attracted much attention and are expected to replace platinum catalysts. Herein, we report an approach to prepare nest-like porous MnCo–P electrocatalyst on the nickel foam by two-step electrodeposition. The prepared bimetallic phosphide MnCo–P₃/NF has excellent hydrogen catalytic activity. In the 1 M NaOH solution, the current density of 10 mA cm^?2 required overpotential is only 47 mV, its Tafel slope is 56.4 mV dec^?1, and the higher current density 100 mA cm^?2 required overpotential is only 112 mV. More importantly, the MnCo–P₃/NF catalyst has a long-term stability of electrocatalytic hydrogen evolution. After 24 h catalytic hydrogen evolution test at a constant current density of 20 mA cm^?2, its potential basically does not change. Furthermore, the current density only changes slightly after 1500 cycles of CV test. All these well prove that the prepared MnCo–P₃/NF catalyst has a long-term hydrogen evolution stability. According to performance testing and morphological characterization, the MnCo–P₃/NF has a high hydrogen catalytic activity and stability are due to its larger active area, lower interface charge transfer resistance and stronger mechanical stability. In summary, the study explores a method of preparing bimetallic phosphides as an efficient and stable hydrogen evolution catalyst.