Ni–P alloy@carbon nanotubes immobilized on the framework of Ni foam as a 3D hierarchical porous self-supporting electrode for hydrogen evolution reaction

The development of self-supporting electrodes that exhibited both high efficiency and good durability remained a challenge in the field of hydrogen energy utilisation. Here, we designed a self-supporting 3D hierarchical porous electrode by filling carbon nanotubes (CNTs) loaded with Ni–P alloy into the framework of nickel foam (NF). Firstly, CNTs were decorated with a catalytically active Ni–P alloy via electroless plating (Ni–P@CNTs). Then, the Ni–P@CNTs were filled and anchored onto the framework of NF via electroplating to synthesise a self-supporting electrode (Ni–P@CNTs/NF). The Ni–P@CNTs/NF exhibited an excellent catalytic performance toward the hydrogen evolution reaction (HER) in 1 M KOH electrolyte, with an overpotential of 53 mV at 10 mA cm^?2, a small Tafel slope of 101.56 mV dec^?1 and excellent long-term durability. This facile and effective strategy might provide a new path to the design of self-supporting electrodes with enhanced HER catalytic.     

The effect of deposition temperature on the catalytic activity of Ni–P alloys toward the hydrogen reaction

The deposition of Ni–P alloys in the temperature range from 0°C to 60°C has been studied. At low temperatures only Ni was deposited. With increasing temperature the amount of P in the deposited alloy increases. The proposed explanation is based on the known reaction mechanisms for electrodeposition and electroless deposition. The catalytic activity of the deposited alloys towards the hydrogen reaction was determined. The highest activity was found at 25°C.     

Preparation of Ni–P–La alloy as a novel electrocatalysts for hydrogen evolution reaction

Ternary Ni–P–La alloy was synthesized by the co-electrodeposition method on the copper substrate. The energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used for characterization of the synthesized alloy. The electrochemical performance of the novel alloy was investigated based on electrochemical data obtained from steady-state polarization, Tafel curves, linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) in alkaline solution and at ambient temperature. The results showed that the microstructural properties play a vital purpose in determining the electrocatalytic activity of the novel alloys. Also, the HER on investigated alloys was performed via the Volmer-Heyrovsky mechanism and Volmer step as RDS in this work. Ni–P–La catalyst was specified by ƞ₂₅₀ = −139.0 mV, b = −93.0 mV dec⁻¹, and j_o = −181.0 μA cm⁻². The results revealed that the Ni–P–La catalysts have a high potential for HER electrocatalysts in 1M NaOH solution.     

Synergistic Co–P bonding effect on hydrogen evolution reaction activity and supercapacitor applications of CoMoP material

Due to the synergistic effect between transition metals and hetero-atoms, transition metal-phosphide-based composites have been used as electrode materials for electrocatalytic hydrogen evolution reactions (HER) and supercapacitors, but their ideal performance has yet to be achieved. Herein, the binary transition metal phosphides, CoMoP and NiMoP, were grown on Ni-foam using a two-step hydrothermal approach and phosphorus deposition in a tube furnace. Both the CoMoP and NiMoP materials showed promising HER activity, displaying an overpotential of 137 mV and 144 mV @10 mA/cm², respectively. The theoretical studies demonstrated that the ΔG_H1 on CoMoP (?0.28 eV) was closer to zero than on NiMoP (?0.34 eV), due to the synergistic Co–P bonding, making it more accessible for H-adsorption, thereby endowing HER. In addition, the CoMoP and NiMoP materials exhibited 3507 F/g and 930 F/g energy storage capacities, respectively. Moreover, both samples had close to 100% Coulombic efficiency and about 50% capacitance retention. Based on these findings, it looks like CoMoP could be good for both the HER and supercapacitor electrodes.     

In situ growth of Ni0·85Se on graphene as a robust electrocatalyst for hydrogen evolution reaction

Seeking the efficient and robust electrocatalysts necessarily enhances performance of hydrogen evolution reaction (HER). Increasing the surface active sites is a means to improve the performance. Herein, we use the Ni_0·85Se anchored on reduction of graphene oxide (Ni_0·85Se/rGO) hybrid material skillfully established by one-step facile hydrothermal method as a robust and stable electrocatalyst applying to hydrogen evolution reaction (HER). In terms of morphology, Ni_0·85Se nanospheres composed of many nanosheets are uniformly distributed on the graphene sheet layer. We also detailedly analyze its properties. Based on the interaction between Ni_0·85Se and rGO, and the roles of graphene are as a substrate to heighten conductivity, possesses more active surface area by limiting growth of Ni_0·85Se, and increases dispersion for exposing more active surface area and enlarge ion/electron transfer rate. In HER, the Ni_0·85Se/rGO catalyst displays the overpotential of 128 mV with a common current density of 10 mA cm⁻², a small Tafel slope of 91 mV dec⁻¹, an extremely low onset potential of 37 mV, outstanding stability that a high current retention of 97.7% after 1000 cycles and well long-term stability for 18 h, outperforming the capability of Ni_0·85Se nanospheres in alkaline solution for HER. The above results indicate that the Ni_0·85Se/rGO hybrid material is a good HER ability and non-noble metal electrocatalyst has potential value in HER.     

Cu–MoS2/rGO hybrid material for enhanced hydrogen evolution reaction performance

Cu doped MoS₂ (Cu–MoS₂)/reduced graphene oxide (rGO) (Cu–MoS₂/rGO) hybrid material is fabricated by a facile one-step solvothermal method. The X-ray diffraction (XRD) results suggest that the doping of Cu does not alter the crystal structure of MoS₂. X-ray photoelectron spectroscopy (XPS) analysis reveal that the doping of Cu atoms influences the electronic structure of MoS₂, which is favorable to increase active sites of edges. Electrochemical impedance spectroscopy (EIS) results indicate that Cu–MoS₂/rGO performed a faster charge-transfer in comparison to MoS₂/rGO hybrid. In addition, the resultant Cu–MoS₂/rGO catalyst with Cu/Mo mole ratio of 9% exhibits a lower overpotential of 199 mV at 10 mA cm⁻², small Tafel slop of 44 mV dec⁻¹ and cycling stability, indicative of enhanced electrocatalytic activity towards HER. The improved performance is attributed to the increased active sites and a synergistic effect between copper and molybdenum, leading to electronic structure change and charge redistribution of MoS₂.     

Facile one-step fabrication of bimetallic Co–Ni–P hollow nanospheres anchored on reduced graphene oxide as highly efficient electrocatalyst for hydrogen evolution reaction

It is significant but challenging to develop noble-metal-free electrocatalysts exhibiting high activity and long-term stability toward hydrogen evolution reaction (HER) to satisfy the ever-increasing demand for clean and renewable energy. Herein, an environment-friendly and low-temperature electroless deposition method is developed for the synthesis of Co–Ni–P hollow nanospheres anchored on reduced graphene oxide nanosheets (Co–Ni–P/RGO). By optimizing the molar ratio of Ni/Co precursor, composition dependent electrocatalytic performances toward HER of nanostructured Co–Ni–P/RGO electrocatalyst are investigated in 1.0 M KOH solution. The results suggest that when the molar ratio of Ni/Co precursor is 3/7, as-prepared ternary Co–Ni–P/RGO electrocatalyst exhibits a remarkably enhanced HER activity in comparison to binary Ni–P/RGO and Co–P/RGO electrocatalysts, delivering a current density of 10 mA cm⁻² at the overpotential of only 207 mV. The value of Tafel slope for nanostructured Co–Ni–P/RGO electrocatalyst reveals that HER process undergoes Volmer-Heyrovsky mechanism. Besides, nanostructured Co–Ni–P/RGO electrocatalyst features superior stability under alkaline condition. The results suggest that nanostructured composite of Co–Ni–P hollow nanospheres/RGO is a potential candidate for hydrogen production through water splitting.     

One-step potentiostatic electrodeposition of Ni–Se–Mo film on Ni foam for alkaline hydrogen evolution reaction

Exploring efficient, abundant, low-cost and stable materials for hydrogen evolution reaction (HER) is highly desired but still a challenging task. Herein, Ni–Se–Mo electrocatalysts supported on nickel foam (NF) substrate were synthesized by a facile one-step electrodeposition method. The Ni–Se–Mo film presents high electrocatalytic activity and stability toward HER, with a low overpotential of 101 mV to afford a current density of 10 mA cm⁻² in 1.0 M KOH medium. Such excellent HER performance of Ni–Se–Mo film induced by the synergistic effects from Mo-doped Ni–Se film leads to the fast electron transfer. This work provides the validity of interface engineering strategy in preparing highly efficient transition metal chalcogenides based HER electrocatalysts.     

Direct synthesis of binder-free Ni–Fe–S on Ni foam as superior electrocatalysts for hydrogen evolution reaction

Designing the efficient, low-cost and stable electrocatalyst is of great significance for storage and conversion of the renewable energy to hydrogen. Herein, the binder-free Ni–Fe–S electrocatalysts were directly electrodeposited on Ni foam, which exhibited the excellent hydrogen evolution reaction performance with the overpotential of 51.4 mV at the current density of 10 mA cm^?2. Based on the analysis and results of as-synthesized Ni, Ni–Fe and Ni–S, the boosted electrocatalytic activity can be attributed to the composite effect between Ni and the introduced Fe and S. Additionally, the Ni–Fe–S electrocatalysts also displayed the low cell voltage (1.59 V at 10 mA cm^?2), remarkable durability and high Faraday efficiency in overall water electrocatalysis. Moreover, the water electrolysis device with Ni–Fe–S bi-electrodes can be driven by a small wind power generation and producing 4 mL H₂ in 39 min, indicating the prepared Ni–Fe–S electrocatalyst has the great potentials in producing hydrogen via renewable energy.     

Effect of carbon content on Ni–Fe–C electrodes for hydrogen evolution reaction in seawater

Hydrogen evolution reaction (HER) on the Ni–Fe–C electrodes electrodeposited at current density ranging from 100 to 300 A/m², as well as their electrochemical properties in 3.5% NaCl solution at 90 °C and pH = 12, had been investigated by polarization measurements, EIS technique. It was shown that the carbon content and grain size of Ni–Fe–C coatings are affected by current density. In addition, the hydrogen evolution overpotential of Ni–Fe–C electrodes was related with carbon content and grain size. The Ni–Fe–C electrodes with optimum catalytic activity for the HER were found to contain the maximum carbon content 1.59% and the minimum grain size 3.4 nm. The results of a comparative analysis between carbon content and intrinsic activity are that carbon content plays an important role in intrinsic activity of Ni–Fe–C electrodes.     

Potentiostatic electrodeposited of Ni–Fe–Sn on Ni foam served as an excellent electrocatalyst for hydrogen evolution reaction

Ni–Fe–Sn electrocatalyst supported on nickel foam (Ni–Fe–Sn/NF) with high efficiency of hydrogen evolution reaction (HER) has been successfully fabricated through one-step potentiostatic electrodeposition route. The optimized Ni–Fe–Sn/NF displayed an extremely low overpotential of, respectively, 144 and 180 mV at 50 and 100 mA cm^?2 for HER in alkaline condition. Moreover, it could retain its superior stability for at least 12 h. The remarkable electrocatalytic activity of our electrocatalyst is ascribed to the high conductivity originated from synergistic effects between Ni, Fe, and Sn during HER process.     

Tuning of electrocatalytic activity of Mn–O–Co composite for alkaline hydrogen evolution reaction

We report the enhancement in electrocatalytic activity of Mn–O–Co composite electrode developed through chemical reduction method. The Mn–O–Co composite electrode exhibits high catalytic activity with a low Tafel slope of 123 mV dec⁻¹ and a low overpotential of 117 mV at a current density of 10 mA cm⁻². The enhancement in electrocatalytic activity of Mn–O–Co composite electrode is due to the synergistic activity of MnO and CoO with the NiP matrix. The intermetallic interaction among the half-filled orbitals of manganese with the fully occupied orbitals of cobalt and nickel leads to an effective electron delocalization in the catalytic system which enhances the HER performance of the coating. The C_dl value of the composite electrode is in the order of 254 μF, which is approximately ten fold higher than the bare NiP coating, due to the enhancement in interaction between the Mn–O–Co composite electrode and the reactive species in the HER medium. The Mn–O–Co composite electrode shows promising characteristics as an electrocatalyst with long term stability and remarkable competency with the commercially available electrodes.     

Lead cathodes functionalized with magnetite particles with enhanced electrocatalytic activity for hydrogen evolution reaction in sulfuric acid solutions

The generation of molecular hydrogen through the electrochemical water splitting process has been extensively studied, due to the potential application of hydrogen to produce green energy with fuel cells. Researchers have been focused in the synthesis of electrocatalysts for the hydrogen evolution. The accumulative roll bonding (ARB) is a promising method which can process a large quantity of an electrode for industrial demand. In this research the ARB process is employed to synthesize lead base electrodes functionalized with magnetite particles (Fe₃O₄) to evaluate their electrocatalytic properties on the hydrogen evolution reaction (HER) in sulfuric acid solutions. SEM, EDS and FESEM techniques are used to characterize the functionalized lead cathodes. The effect of rolling passes, magnetite concentration, and suspended magnetite particles on the HER kinetics is studied using linear voltammetry, Tafel plots, and electrochemical impedance spectroscopy (EIS). The results revealed that lead cathodes functionalized with magnetite present great advantages over lead cathodes, such as: a decrease of 0.37 V in HER over-potential, an increase of 84.3 times in the exchange current density, a decrease in the charge transfer resistance of 98%. From a mechanistic viewpoint, HER is catalyzed by the presence of Fe²⁺ adsorbed on the lead cathode; ferrous ions are produced from the reductive dissolution of magnetite particles. Long-term electrolysis and multiple cyclic voltammetry tests (800 polarization cycles) revealed that the catalytic effect is maintained during 44 h of operation. According to the Tafel curves and EIS results, the Volmer reaction is the rate determining step of the HER on these functionalized cathodes.     

Boosting activity and stability by coupling Pt–Ni nanoparticles with La-modified flexible carbon nanofibers for hydrogen evolution reaction

Platinum (Pt) is considered as the most efficient catalyst for hydrogen evolution reaction (HER) with a nearly zero overpotential, but it is limited by the high cost and poor stability. Herein, we report an efficient electrocatalyst of Pt–Ni alloy nanoparticles (NPs) supported on the La-modified flexible carbon nanocomposite fibers (PtNi@La-CNFs) for HER. The rare earth metal oxide in the catalyst has a structure-effect relationship with the carbon fibers to form a flexible fiber membrane. Experimental results show that the macroscopic and microscopic properties of carbon nanocomposite fibers can be optimized by doping La₂O₃, and the Pt–Ni NPs can be anchored effectively. The Pt₁Ni₁@La-CNFs electrocatalyst exhibits a small overpotential of 32 mV to achieve current density of 10 mA cm^?2 with a low Tafel slope of 51 mV dec^?1 in alkaline medium, outperforming that of Pt@La-CNFs and the commercial Pt/C catalyst. This study reveals that the multiple coupling effect of rare earth compound, precious metal, and transition metal in composite catalyst can tailor its the electronic configuration, and results in an enhanced HER performance. This work opens up a novel approach to design high active and low cost Pt-based HER catalysts.     

Potentiostatic electrodeposition of cost-effective and efficient Ni–Fe electrocatalysts on Ni foam for the alkaline hydrogen evolution reaction

The hydrogen evolution reaction (HER) using earth-abundant noble-metal-free catalysts has gained substantial interest in electrocatalytic water splitting technologies, particularly in water-alkali electrolyzers. The development of highly-efficiency and durable inexpensive electrocatalysts to accelerate the kinetics of HER is still a formidable challenge. In this study, nickel–iron (Ni–Fe) electrocatalyst directly grown on backbones of Ni foam (NF) substrate was facile prepared via one-step potentiostatic electrodeposition method. The obtained Ni–Fe electrocatalyst exhibits a film-like structure. Owing to high electrical conductivity and composition optimization, the synthesized Ni–Fe electrocatalyst with Ni/Fe atomic ratio of c.a. 65:35 possesses an attractive electrocatalytic activity with low overpotentials of 142, 205, and 239 mV at 10, 50, and 100 mA·cm^?2 in alkaline electrolyte, respectively.     

Effect of microstructure on the electrocatalytic activity for hydrogen evolution of amorphous and nanocrystalline Zr–Ni alloys

Rapidly quenched Zr₂Ni amorphous and nanocrystalline ribbons were studied as electrocatalysts for hydrogen evolution in 6 M KOH. Linear polarization, potentiostatic hydrogen charge/discharge and EIS measurements at various potentials were carried out for the Zr alloys with different microstructure with the aim to extract information about the mechanism of hydrogen evolution and absorption and estimate the kinetic parameters of the hydrogen evolution reaction (HER). Though the melt-spun Zr₆₇Ni₃₃ alloys with varying microstructure do not show substantially different catalytic activity for HER, it could be clearly demonstrated that the nanocrystalline material reveals better catalytic performance than the entirely amorphous and nano-/amorphous alloys with the same chemical composition. It was found that all studied Zr–Ni alloys absorb hydrogen under the conditions of the hydrogen evolution experiments, as the amount of the absorbed hydrogen depends to a large degree on the alloys microstructure as well as on the applied potential during the HER experiment. The diffusion coefficient of hydrogen into the amorphous Zr₆₇Ni₃₃ alloy, as well as the thickness of the hydrided layer were found to be noticeably larger than those of the nanocrystalline alloy at the same conditions of hydrogen charging. Therefore the improved electrocatalytic properties of the nanocrystalline alloy could only be explained by its favorable microstructure (e.g. higher density of defects) and weaker hydrogen absorption into the nanostructured material under the conditions of the HER.     

A low-cost platinum-free electrocatalyst based on carbon quantum dots decorated Ni–Cu hierarchical nanocomposites for hydrogen evolution reaction

The effective Ni–Cu bimetallic nanocomposite was deposited on a glassy carbon electrode, GCE, that modified with carbon quantum dots, CQDs. The deposition process was done by one-step and controllable electrochemical method in an electrolyte of nickel and copper sulfate. The structural properties of composite studied by techniques such as X-ray diffraction, XRD, energy dispersive X-ray analysis, EDX, field emission scanning electron microscopy, FESEM, and transmission electron microscopy, TEM. Ni–Cu/RCQDs nanocomposite was applied as a cathode for catalysis of hydrogen evolution reaction, HER, in acidic media by cyclic voltammetry, CV, linear sweep voltammetry, LSV, chronoamperometry, CA, and electrochemical impedance spectroscopy, EIS. The onset potential, E_onset, for the evolution of hydrogen at the current density of −10 mA cm⁻² for Ni–Cu/RCQDs was −230 mV vs. SHE that had a 100 mV shift to positive voltages in comparison with Ni–Cu catalyst. It can be related to the synergistic effect between metallic nanoparticles. V. dec⁻¹, respectively.     

A novel Ni–La-Nd-Y flim on Ni foam to enhance hydrogen evolution reaction in alkaline media

The exploration of non-precious metal catalysts has always been a hot topic. Here, a new type of Ni–La-Nd-Y film was electrodeposited on nickel foam (NF). The Ni–La-Nd-Y film shows outstanding HER activity and stability under alkaline conditions. La₂NiO₄ makes the electrode surface present a regular layered structure, which greatly increases the number of electrochemically active sites. Ni–La-Nd-Y only needs 46 mV overpotential driving current density of 10  mA cm^?2 in 1MKOH solution, which is very close to the HER performance of metal Pt. By doping rare earth elements and taking advantage of the shrinkage characteristics of lanthanides, this work took advantage of the shrinkage characteristics of the lanthanide series and found new ideas for improving catalysts through the combination of different rare earth elements.     

Electrochemical performance of hydrogen evolution reaction of Ni–Mo electrodes obtained by mechanical alloying

Electro active Ni–Mo electrodes have been prepared by mechanical alloying and pressure-less sintering $\text{(1173}\text{K}\text{)}$ Ni and Mo powders. The electrochemical performance of obtained electrodes has been evaluated in KOH 30% at $\text{343}\text{K}$ as a function of the milling time, applied pressure for green compaction as well as the effect conferred by the addition of a process control agent (PCA). Cathodic slope of the best specimen is $\text{279}\text{mV}\text{/}\text{dec}$. Faster reaction kinetics is observed for the specimens treated with PCA addition. The longer milling time and applied pressure on the specimens the better cathodic response. The activation overpotential, i.e. cathodic-Tafel slopes found at high overvoltages are in the range of 274–$\text{481}\text{mV}\text{/}\text{dec}$, whereas the exchange current density for the hydrogen evolution reaction ranged from 27.3 to $\text{1.4}\text{mA}\text{/}\text{cm}{}^2$.     

Kinetics of hydrogen evolution reaction on stabilized Ni,Pt and Ni–Pt nanoparticles obtained by an organometallic approach

Both (Ni, Pt) and bimetallic (Ni_xPt; x = 1, 2, 3) nanoparticles have been synthesized by hydrogenation of Ni(cod)₂ ad Pt₂(dba)₃ in the presence of a weak coordinating ligand, hexadecylamine (CH₃(CH₂)₁₅NH_2, HDA). These nanostructures were characterized by different techniques (Fourier Transform-Infrared Spectroscopy (FT-IR), High-Resolution Transmission Electron Microscopy (HRTEM)), and were evaluated as Hydrogen Evolution Reaction electrocatalysts in 0.5 M sulfuric acid. The effects of varying the platinum amount during the synthesis were systematically studied by Cyclic Voltammetry (CV), polarization measurements and electrochemical impedance spectroscopy (EIS) techniques. HRTEM shows that the bimetallic nanostructures display a different morphology compared to that observed for pure Ni and Pt ones. The process of hydrogen adsorption–desorption in the as-prepared electrodes seems to occur in (110) and (100) facets. It was found that the increase in the activity for the HER is due to an increased electrochemical active surface area (ECSA) and/or stabilization in the case of elemental electrode materials; and to the effect of Pt amount in the case of the Ni–Pt nanostructures (synergistic effect leads to lower overpotential). It has been established that the main pathway for the HER is Volmer–Heyrovsky.