Direct-current electrodeposition of Ni–S–Fe alloy for hydrogen evolution reaction in alkaline solution

Ni–S–Fe alloy has been successfully fabricated on a copper foil substrate through direct-current electrodeposition as an electrocatalyst for hydrogen evolution reaction (HER) in alkaline solution. The Ni–S–Fe alloy is characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The electrocatalytic performance of Ni–S–Fe alloy for HER is studied in 30 wt% KOH solution. The results show that the Ni–S–Fe alloy exhibits much higher catalytic activity for HER relative to Ni–S alloy, as manifested by smaller overpotential of 222 mV at 10 mA cm^?2 and higher exchange current density of 1.60 × 10^?2 mA cm^?2. The Tafel slope of 84.5 mV·dec^?1 implies an underlying Volmer-Heyrovsky mechanism. The outstanding catalytic performance of the Ni–S–Fe alloy may originate from the synergistic effects of Ni and Fe, refined grain, and enlarged surface area of Ni–S–Fe alloy upon Fe doping. In addition, the Ni–S–Fe alloy has better anti-corrosion property than Ni–S alloy as a result of the poorer crystallinity of Ni–S–Fe alloy.     

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.     

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.     

One-step electrodeposition of cauliflower-like Ni–Fe–Sn particles as a highly-efficient electrocatalyst for the hydrogen evolution reaction

Herein, a Ni–Fe–Sn coating was synthesized in-situ on Ni mesh by one-step electrodeposition at different durations. The Ni–Fe–Sn60 electrode obtained after 1 h deposition exhibits cauliflower-like morphology and the best electrocatalytic properties for the hydrogen evolution reaction (HER) compared to other electrodes. The electrode requires an overpotential of 43 mV at a current density of 10 mA cm⁻² and a small Tafel slope of 70 mV dec⁻¹ in a 1 M KOH solution. Moreover, the electrode shows outstanding stability in prolonged electrolysis and overall water splitting performance, generating a current density of 93 mA cm⁻² at 1.8 V, which is thrice that of an industry electrode. This electrocatalytic activity is ascribed to the high active surface area produced by the cauliflower-like Ni–Fe–Sn particles and the synergistic interaction of Ni, Fe and Sn. The simple synthesis method and excellent performance endow this electrode with great potential for large-scale applications.     

Solidification microstructure-dependent hydrogen generation behavior of Al–Sn and Al–Fe alloys in alkaline medium

This work deals with the development of quantitative correlations of hydrogen evolution performance with solidification microstructural and thermal parameters in Al–1Sn, Al–2Sn, Al–1Fe, and Al-1.5Fe [wt.%] alloys. The cellular growth as a function of growth and cooling rates is evaluated using power type experimental laws, which allow determining representative intervals of microstructure length scale for comparison purposes with the results of immersion tests in 5 wt%NaOH solution. For both Al alloys systems, hydrogen evolution becomes slower as the alloy solute content increased. However, for a given alloy composition, whereas a more homogeneous distribution of Sn-rich particles promotes faster hydrogen generation using Al–Sn alloys, coarsening of Al₆Fe IMCs (intermetallic compounds) fibers favors hydrogen production using Al–Fe alloys. When solidification conditions that result in a range of cellular spacings within 16 and 19 μm are considered, the specific hydrogen production of the Al-1wt.%Fe alloy is higher than that of the other studied alloys.     

Fabrication of Mg–Ni–Sn alloys for fast hydrogen generation in seawater

Mg-2.7Ni-x wt.% Sn(x = 0–2) alloys were fabricated to promote hydrogen generation kinetics of Mg-2.7Ni alloy. The Sn in Mg-2.7Ni-Sn alloys exists as Mg₂Sn phase at the grain boundary and solid solution at the Mg matrix. The Mg₂Sn at the grain boundary acts as the initiation site for pitting corrosion and the dissolved Sn in the alloy causes pitting corrosion by locally breaking the surface oxide film in the Mg matrix in seawater. The Mg-2.7Ni-1Sn alloy showed an excellent hydrogen generation rate of 28.71 ml min^?1 g^?1, which is 1700 times faster than that of pure Mg due to the combined action of galvanic and intergranular corrosion as well as pitting corrosion in seawater. As the solution temperature was increased from 30 to 70 °C, the hydrogen generation rate from the hydrolysis of the Mg-2.7Ni-1Sn alloy was dramatically increased from 34 to 257.3 ml min^?1 g^?1. The activation energy for the hydrolysis of Mg was calculated to be 43.13 kJ mol^?1.     

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.     

Efficient and stable Ni–Co–Fe–P nanosheet arrays on Ni foam for alkaline and neutral hydrogen evolution

The development of highly efficient and superior durability electrocatalysts is vital to expedite hydrogen evolution reaction (HER). Herein, a mixed amorphous and nano-crystalline Ni–Co–Fe–P alloy on Ni foam after 75 s dealloying in 3 M HCl (Ni–Co–Fe–P/NF-3-75) is synthesized by the preparation strategy of two-step method consisting of electroless deposition and dealloying process. Ni–Co–Fe–P/NF-3-75 shows an excellent HER performance and high durability in both alkaline and neutral conditions by optimizing the composition of the catalysts, acid concentration, and the time of dealloying. Benefitting from the high conductivity of Ni foam carrier, coordination between polymetallic phases, and the large exposure of defects, the as-prepared Ni–Co–Fe–P/NF-3-75 requires only a low overpotential of 56 mV and 104 mV to reach the current density of 10 mA cm⁻² in 1.0 M KOH and 1.0 M phosphate buffer (PBS), respectively. Remarkably, the Ni–Co–Fe–P/NF-3-75 electrode exhibits superior cycling stability and long-term robust durability without obvious overpotential decline. The successful preparation of the Ni–Co–Fe–P/NF-3-75 catalyst indicates that this method provides an efficient way to synthesize polymetallic phosphides for hydrogen evolution reaction.     

Properties of mechanically alloyed Mg–Ni–Ti ternary hydrogen storage alloys for Ni-MH batteries

MgNiTi_x, Mg_1−xTi_xNi and MgNi_1−xTi_x (with x varying from 0 to 0.5) alloys have been prepared by high energy ball milling and tested as hydrogen storage electrodes. The initial discharge capacities of the Mg–Ni–Ti ternary alloys are inferior to the MgNi electrode capacity. However, an exception is observed with MgNi_0.95Ti_0.05, which has an initial discharge capacity of 575 mAh/g compared to 522 mAh/g for the MgNi electrode. The Mg–Ni-Ti ternary alloys show improved cycle life compared to Mg–Ni binary alloys with the same Mg/Ni atomic ratio. The best cycle life is observed with Mg_0.5Ti_0.5Ni electrode which retains 75% of initial capacity after 10 cycles in comparison to 39% for MgNi electrodes, in addition to improved high-rate dischargeability (HRD). According to the XPS analysis, the cycle life improvement of the Mg_0.5Ti_0.5Ni electrode can be related to the formation of TiO₂ which limits Mg(OH)₂ formation. The anodic polarization curve of Mg_0.5Ti_0.5Ni electrode shows that the current related to the active/passive transition is much less important and that the passive region is more extended than for the MgNi electrode but the corrosion of the electrode is still significant. This suggests that the cycle life improvement would be also associated with a decrease of the particle pulverization upon cycling.     

In situ activation with Mo of Ni–Co alloys for hydrogen evolution reaction

In this study Ni–Co alloys have been activated during hydrogen electrochemical production by adding Mo ions into the alkaline electrolyte. After dissolving different amounts of sodium molybdate in the Na(OH) electrolyte, Ni–Co alloys were used as cathodes for hydrogen evolution reaction. Afterwards a comparison between hydrogen overvoltage measured on Ni–Co alloys with and without in situ activation has been made. The in situ activation clearly shows an improvement of electrocatalytic properties of Ni–Co alloys for hydrogen evolution reaction. Depending on the alloy the best conditions are reached with different amounts of sodium molybdate in the electrolyte. The values of exchange current density for Ni–Co alloys without Mo, are an average of about 4.1 10⁻⁶ A/cm², while by using in situ activation, these values are about 3.5·10⁻⁴ A/cm². Therefore, exchange current density presents a value nearly one hundred-fold higher when molybdate ions are present in solution. Moreover, two Tafel slope values have been determined for HER on Ni–Co alloys with and without Mo in situ activation. Those Tafel slope values are different, so as their range of both overvoltage and current density, probably highlighting a different kinetic mechanism.     

New La–Fe–B ternary system hydrogen storage alloys

The new La₈Fe₂₈B₂₄-, La₁₅Fe₇₇B₈- and La₁₇Fe₇₆B₇-type alloys have multiphase structures including LaNi₅, La₃Ni₁₃B₂ and (Fe, Ni) phases. The amount of La₃Ni₁₃B₂ phase increased and that of (Fe, Ni) phase decreased with an increasing La/(Fe + B) atomic ratio. The measurement of P–C–I curves revealed that the maximum hydrogen capacity exceeded 1.12 wt% at 313 K in the pressure range of 10⁻³ MPa–2.0 MPa. The alloys exhibited good absorption/desorption kinetics at room temperature, and electrochemical experiments showed that all of the alloy electrodes exhibited good activation characteristics, high-rate dischargeability (HRD) and low-temperature (233 K) dischargeability (LTD).     

Influence of electrodeposition parameters of Ni–W on Ni cathode for alkaline water electrolyser

In this study, different Ni–W coatings, obtained by cheap and technologically simple electrodeposition method, were examined as potential electrocatalysts for the hydrogen evolution reaction (HER). All electrodepositions were done on a Ni mesh substrate from ammoniacal-citrate bath containing different concentrations of Na₂WO₄. The influence of deposition parameters, such as deposition current density, pH and composition of ammoniacal-citrate bath on electrocatalytic activity of obtained Ni–W coatings toward HER was examined by polarization curve measurements in 6 M KOH at room temperature. The morphology and tungsten content of the Ni–W coatings were investigated by means of SEM and EDS analysis. All investigated electrodes have shown high electrocatalytic activity for the HER. The samples obtained at higher deposition current densities had the lowest overvoltage for the HER. It has been shown that the plating bath pH value is very important parameter in obtaining active coatings. Results of the analysis of polarization curves, morphology of deposited Ni–W coatings and the content of tungsten in the coatings, indicate that the surface roughness of the coatings is responsible for their catalytic activity towards HER.     

Electrodeposition of Ni–Fe–Mn ternary nanosheets as affordable and efficient electrocatalyst for both hydrogen and oxygen evolution reactions

The synthesis of high performance and economical electrocatalysts in the process of overall water splitting is very important for the production of hydrogen energy and has become one of the most important challenges. Here, various Ni, Ni–Fe, Ni–Mn nanosheets and Ni–Fe–Mn ternary nanosheets were created using cost-effective, versatile and binder-free electrochemical deposition methods, and the electrocatalytic activity of various electrodes for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) were investigated in an alkaline environment. Due to the high electrochemical active surface area due to the fabrication of nanosheets, the synergistic effect between different elements on the electronic structure, the high wettability due to the formation of nanosheets and the quick detachment of formed gasses from the electrode, the Ni–Fe–Mn nanosheets electrode showed excellent electrocatalytic activity. In order to deliver the 10 mA cm⁻² current density in HER and OER processes, this electrode required values of 64 mV and 230 mV overpotential, respectively. Also, the stability test showed that after 10 h of electrolysis at a current density of 100 mA cm⁻², the overpotential changes was very small (less than 4%), indicating that the electrode was excellent electrostatic stability. Also, when using as a bi-functional electrode in the full water splitting system, it only needed a cell voltage of 1528 V to deliver a current of 10 mA cm⁻². The results of this study indicate a new strategy for the synthesis of active and stable electrocatalysts.     

Nickel-doped MoSe2 nanosheets with Ni–Se bond for alkaline electrocatalytic hydrogen evolution

Molybdenum diselenide (MoSe₂) is a potential catalytic material for the electrocatalytic hydrogen evolution reaction (HER). However, due to the low density of its active sites, MoSe₂ nanosheets feature high overpotential in HER, which limits its practical application. This describes the method of doping the Ni in MoSe₂ nanosheets to increase active sites. The NiO₂ evenly dispersed on MoSe₂ by ethanol solution reduces to ~4 nm Ni nanoclusters under annealing process, which is firmly adhered to MoSe₂ nanosheets with Ni–Se bond. The electrochemical active surface area of Ni-doped MoSe₂ expands, proving that Ni dopants produce more activity sites in MoSe₂ nanosheets. The overpotential of MoSe₂ (at 10 mA cm⁻²) decreases from 335 mV to 181 mV with 4.5 at.% Ni doped in 1 M KOH. The Ni–MoSe₂ also characterizes excellent stability for 12 h with the formation of Ni–Se bond. The study of doping Ni in MoSe₂ nanosheets is of great guiding significance to the design and production of non-noble electrocatalysts for HER in alkaline media.     

Electrodeposition of nickel–copper alloys to use as a cathode for hydrogen evolution in an alkaline media

The electrocatalytic activity of nickel–copper (Ni–Cu) alloy coated electrodes for the hydrogen evolution reaction (HER) in an alkaline media was studied. The Ni–Cu alloys were electrodeposited on a Cu substrate by direct current (DC) and pulse current (PC) electrodeposition in a fixed plating bath. A wide alloy composition range (6–81 mol% Ni) was achieved by controlling the applied current density between 5 and 300 mA cm⁻². It was found that the electrocatalytic activity for the HER depended on the composition of the Ni–Cu alloys, where electrodes having low Ni content gave high electrocatalytic activities. DC electrodeposition resulted in better electrocatalytic performances than PC. Pulse plating parameters other than the magnitude of the applied current density did not substantially influence the electrocatalytic performance of the Ni–Cu alloy electrodes. Ni content was found to have a stronger effect on the electrocatalytic activity for the HER than the deposit morphology.     

Electrodeposition of Ni–Co–Sn alloy from choline chloride-based deep eutectic solvent and characterization as cathode for hydrogen evolution in alkaline solution

The electrodeposition of Ni–Co–Sn alloy were carried out at room temperature from the chlorine chloride (ChCl)–ethylene glycol (EG) deep eutectic solvent (DES). For comparison of properties, Ni–Sn and Co–Sn alloys were also deposited using the same solvent. Deposition mechanism, microstructure, and electrochemical properties of the deposits in 1 M KOH solution were investigated. The deposition of Ni, Co, Sn, Ni–Sn, Co–Sn and Ni–Co–Sn on platinum electrode were also studied using cyclic voltammetry. Interestingly, the electrochemical stability of DES is observed to be increased in the presence of Sn²⁺ ions. The X-ray diffraction (XRD) patterns showed only Ni phases indicating that the other elements get incorporated inside the nickel matrix and the lattice constant have linear relation with Sn content in alloy. The morphologies of Ni–Sn and Ni–Co–Sn alloys were observed to be almost same with fine grains, the XRD studies confirm this. The potentiodynamic polarization measurements showed that the Ni–Co–Sn alloy exhibits the lowest corrosion current density (j_corr), noblest corrosion potential (E_corr) and highest exchange current density (j_c) value than the other two binary alloys, indicating that the ternary alloy is a good candidate for Hydrogen Evolution Reaction (HER).     

Study on Ni–Fe–C cathode for hydrogen evolution from seawater electrolysis

Hydrogen evolution reaction in 3.5 wt% NaCl (simulated seawater) was investigated using Ni–Fe–C cathode, prepared by cathode electrodeposits method on the matrix of A3 steel. The as-prepared Ni–Fe–C cathode coating materials has reached nanometer grade, what is more, the limit of average grain size was about 4.3 nm. As decreasing of the average coating grain sizes, hydrogen evolution overpotential was not decreasing linearly. There was a boundary average coating grain sizes of about 4.3–6.4 nm. The optimal preparation process of Ni–Fe–C cathode was listed as electroplating current density 200 A/m², temperature 30 °C, pH 1.5 and 60 min. The hydrogen overpotential was only about 65 mV, which was tested in the 3.5 wt% NaCl of 90 °C at pH 12.     

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.     

Ni–Cr alloys for effectively enhancing hydrogen evolution processes in phosphate-buffered neutral electrolytes

Significant efforts have been made to develop highly active non-noble metal-based, affordable metallic and stable electro-catalysts for hydrogen evolution reaction (HER). Strong acid and bases are now used in HER operations to achieve large-scale, sustained H₂ fuel production. However, few studies have utilized phosphate-buffered neutral electrolytes (PBS) in the field of neutral electrolyte technology. In this work, a certain alloys with a Ni–Cr basis have been produced as favorable components for the HER under neutral conditions. Additionally, the current investigations are emphasizing on the concentration of buffer phosphate species in the HER activity of various materials. By employing polarization and electrochemical impedance spectroscopy (EIS) in neutral solutions, the electro-catalytic activity of new alloys on HER was evaluated. According to the preliminary findings, the examined Ni–Cr-based alloys show superior HER catalytic activity in neutral electrolytes. Additionally, the Ni–Cr alloy matrix with Fe and Mo added enhances HER electrocatalytic efficiency while lowering interfacial charge transfer resistance. Due to its low overpotential of ?297 mV @ 10 mA cm^?2 and Tafel slope of 94 mV dec^?1 in 1.0 M PBS media, the Ni–Cr–Mo–Fe alloy exhibits an efficient HER, suggesting that the Ni–Cr–Mo–Fe electrode will be a potential noble metal-free electro-catalyst for HER. The Ni–Cr–Mo–Fe cathode is a readily available and affordable material for the production of HER in neutral medium.     

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.