Effect of current change on iron-copper-nickel coating on nickel foam for hydrogen production

Electrochemical iron-copper-nickel coatings on nickel mesh with two electrode technique were performed galvanostatically. The current density and the durations are changed during the coatings and the coatings are applied at different currents but at constant charge. All electrodepositions were applied under the same charge. In this study, different compositions of iron-copper-nickel on nickel foam under the constant charge were prepared electrochemically and characterized in view of their possible applications as electrocatalytic materials for the hydrogen evolution reaction (HER) in the alkaline medium. The HER activity of prepared electrodes has been investigated by using cyclic voltammetry (CV), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques in 1 M KOH solution. As it is seen from the results that the electrode prepared by depositing at a current 4 mA during 1800 s is the most active catalyst for HER.     

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.     

Synthesis and characterization of macroporous Ni,Co and Ni–Co electrocatalytic deposits for hydrogen evolution reaction in alkaline media

In this work, macroporous Ni, Co and Ni–Co electrodes have been developed by co-deposition at high current density on stainless steel (AISI 304) substrates. The obtained materials were characterized both morphologically and chemically by confocal laser scanning microscopy, and SEM coupled with EDX analysis. The activity for hydrogen evolution reaction (HER) on the obtained layers was assessed by using pseudo-steady-state polarization curves and electrochemical impedance spectroscopy (EIS) in alkaline solution (30 wt.% KOH). The electrochemical results show that HER on these electrodes takes place by the Volmer–Heyrovsky mechanism. The synthesized coatings present higher catalytic activity for HER than commercial smooth Ni electrode. As the Co content increases in the electrodeposition bath the obtained structures show lower surface roughness factors. Ni–Co deposit with a Co content of 43 at.% manifests the highest intrinsic activity for HER as a consequence of the synergetic combination of Ni and Co.     

The hydrogen evolution reaction on nickel-polyaniline composite electrodes

The electrolytic codeposition of nickel composite coatings with different amounts of polyaniline particles (PAni) was used to produce electrodes for the catalytic hydrogen evolution reaction (HER). The electrodes produced were imaged by scanning electron microscopy, and their catalytic activities for HER were determined by linear Tafel polarization and electrochemical impedance spectroscopy (EIS) in a 0.5 M H₂SO₄ solution. The electron micrographs showed that the amount of exposed polyaniline surface was directly related to the polyaniline concentration in the solution used for the electrolytic codeposition. The linear Tafel polarizations indicated that the HER was limited by the Volmer step, and the EIS measurements showed that the presence of PAni on the electrode surface affected the HER. Electrodes with higher composite contents exhibited enhanced catalytic activity.     

Ni–CeO2 composite cathode material for hydrogen evolution reaction in alkaline electrolyte

In this work, nickel-based electrodes were prepared using composite electrodeposition technique in a nickel sulphamate bath containing suspended micro- or nano-sized CeO₂ particles. The prepared Ni–CeO₂ composite electrodes exhibit an enhanced high catalytic activity toward hydrogen evolution reaction (HER) in alkaline solutions. X-ray diffraction patterns indicated that the CeO₂ particles have been successfully incorporated into the Ni matrix and altered the texture coefficient (TC) of the Ni layer. The morphology of the obtained coatings was characterized by Scanning Electron Microscopy, and the CeO₂ content was determined by coupled energy dispersive X-ray spectrometry. The thermal stability of the composite electrodes was analyzed by thermogravimetric and differential scanning calorimetry, showing a good thermal stability. The catalytic activity of the composite electrodes for HER was measured by steady-state polarization and electrochemical impedance spectroscopy techniques in 1.0 M NaOH solution at room temperature. The exchange current density of HER on the Ni–CeO₂ composite electrodes was much higher than that on Ni electrode. EIS results suggested that a synergetic effect on HER may exist between CeO₂ particles and Ni matrix. Compared to nano-CeO_2, the micro-CeO₂ derived composite electrodes showed higher electrochemical activity. The possible correlation among particle size, content and catalytic activity is discussed.     

Kinetics of the hydrogen evolution reaction on Ni-(Ebonex-supported Ru) composite coatings in alkaline solution

The hydrogen evolution reaction (HER) was studied on Ni, Ni-Ebonex and Ni-(Ebonex-Ru) coatings in 1 mol dm⁻³ NaOH solution at 25 °C. The composite coatings were electrodeposited from a nickel Watts-type bath containing suspended Ebonex (chemical composition mainly Ti₄O₇) or Ebonex-supported Ru(10 wt.%) particles (0–10 g dm⁻³) onto Ni 40 mesh substrate. The electrodes were investigated by cyclic voltammetry (CV), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) in combination with energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS), electrochemical impedance spectroscopy (EIS) and polarization measurements. These investigations showed that the roughness factor of the Ni-(Ebonex-Ru) and the Ni-Ebonex coating was 29 and 6 times higher than that of a pure Ni coating, respectively. In the whole potential range of the HER only one Tafel slope of about −120 mV was present at the polarization curves of Ni and Ni-Ebonex electrodes, with increased activity of the latter being attributed only to the increase of the electrochemically active surface area. The Ni-(Ebonex-Ru) electrodes exhibited the highest intrinsic catalytic activity with two Tafel slopes, indicating also that the HER takes place exclusively on Ru active sites.     

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.     

Improved 3D porous structures of Ni electrodes prepared by high-pressure cold spray and post annealing for water splitting

For improving the performance of water splitting, high pressure cold spray was applied to prepare Ni electrodes with controlled 3D porous structures. Al was added as pore former to endow the Ni electrodes with porous structures. Heat treatment was performed to improve the adhesion of the prepared coatings and thus boost the durability of the obtained Ni electrodes. The electrochemical results and characterizations revealed that porous Ni electrodes were successfully obtained. The porosity of obtained electrodes was increased with the addition of Al. Alloy phases such as NiAl and Ni₃Al were detected after heat treatment. An oxide layer was found surrounding Ni layers after chemical leaching. The thickness of oxide layer was found increased with heating temperature and Al addition. NiO, Ni(OH)₂ and NiOOH were found in the leached samples. With porous coatings, the electrodes possessed an improved current density of HER/OER. The Tafel slops of HER/OER were about 120mv/dec which indicated that the rate of water splitting was controlled by Volmer step. Due to the existence of oxide layers and unconnected pores, some samples exhibited Warburg diffusion behavior. Benefitting from the loose and porous microstructure, N30A sintered at 400 °C performed the best catalytic activity for HER/OER, and is considered the best sample for water splitting in alkaline condition.     

Enhancement of hydrogen evolution at cobalt-zinc deposited graphite electrode in alkaline solution

Thin Co layers were electrochemically deposited on a graphite electrode at different deposition current densities and thicknesses. After determining the best deposition conditions for hydrogen evolution (deposition current density and thickness), co-deposits of Co with Zn were prepared on the graphite electrode. The binary coatings prepared on the graphite electrode (CoZn) were etched in a concentrated alkaline solution (30% NaOH) to produce a porous and electrocatalytic surface suitable for use in the hydrogen evolution reaction (HER). After the leaching process, a low amount of Pt was deposited onto the etched CoZn deposit in order to further improve the catalytic activity of the electrode for the HER. The HER activity is assessed by recording cathodic current-potential curves, electrochemical impedance spectroscopy (EIS) and electrolysis techniques. Chemical composition of layers after alkaline leaching was determined by energy dispersive X-ray (EDX) analysis. The surface morphologies of coatings were investigated by scanning electron microscopy (SEM). It was found that, the HER activity of coatings depends on the metal ratio of Co and Zn, deposition current density and the thickness of coatings. The alkaline leached CoZn coating has a compact and porous structure as well as good electrocatalytic activity for the HER in alkaline media. Moreover, deposition of a low amount of Pt over the CoZn can further enhance its hydrogen evolution activity.     

Enhancement of hydrogen evolution reaction by Pt nanopillar-array electrode in alkaline media and the effect of nanopillar length on the electrode efficiency

Pt nanopillar-array 3D electrodes with nanopillar length of 150, 450 and 900 nm and nanopillar density of ~10⁹ cm⁻² were fabricated. Their catalytic activity for hydrogen evolution reaction (HER) was evaluated by linear sweep voltammetry and electrochemical impedance spectroscopy. In comparison with straightly electrodeposited black Pt film and forged Pt sheet electrodes, the HER current density has been significantly improved by the nanopillar-array architecture. The overpotential of HER at current density of 10 mA cm-2 at 26 °C is as low as 78 mV, lower than the black Pt film of 107 mV and the Pt sheet of 174 mV. The improvement of HER is ascribed to the low charge transfer resistance of the 3D electrode and the high desorption capability of hydrogen bubbles at the nanotips. Interestingly, the nanopillar-array 3D electrode has an optimal nanopillar length for HER. The mechanisms for the optimal nanopillar length were investigated here.     

Ni/Fe electrodes prepared by electrodeposition method over different substrates for oxygen evolution reaction in alkaline medium

A series of Ni/Fe electrodes have been prepared by electrodeposition of metal salt precursors on different substrates. The surface morphology, chemical composition and electrochemical characteristics of these electrodes were studied by various physico-chemical techniques such as X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM). The electrochemical properties of the electrodes were examined by steady-state polarization curves. First, the influence of features such as Ni/Fe composition and type of substrate for the oxygen evolution reaction (OER) were determined by electrochemical techniques in a conventional 3-electrodes cell. The overpotential for the OER is lower for the electrodes with the higher concentrations of Ni. The electrodes with a Ni/Fe composition of 75/25 wt.% electrodeposited on steel mesh and/or 75/25 and 50/50 wt.% on nickel foam result in the most active configurations for the OER. These electrodes were further tested as anodes for alkaline water electrolysis during at least 70 h. In order to understand their activity and stability, the used electrodes were also characterized by SEM and compared to the fresh electrodes. Among the compositions and substrates examined, the Ni50Fe50-Nf electrode exhibited the lowest overpotential (2.1 V) for the OER and the higher stability as anode in an alkaline water electrolysis cell.     

Nickel-polyaniline composite electrodes for hydrogen evolution reaction in alkaline media

In this work, nickel-based electrodes were prepared using a composite electrodeposition technique in a nickel bath containing suspended polyaniline (PAni) particles. The electrodes were characterized by Raman spectroscopy and scanning electron microscopy. The catalytic activity of the composite electrodes for the hydrogen evolution reaction (HER) was measured by cathodic polarization and electrochemical impedance spectroscopy in KOH and KOH with 1 M sucrose at room temperature. The Ni–PAni electrodes showed a high active surface area that contributed to the increase in the current density of HER and to the decrease in overpotential value as compared to Ni electrodes.     

Double-template fabrication of three-dimensional porous nickel electrodes for hydrogen evolution reaction

Three-dimensional (3D) porous nickel structures were fabricated via a double-template electrochemical deposition process. The construction of the foam structures was achieved by means of a hydrogen bubble dynamic template, prepared from Cu electrodeposition at high current densities. Subsequently, a Ni layer was electrodeposited on the Cu 3D template. During the nickel coating, the typical finger-like microstructure of the Cu foam becomes denser and changes to a cauliflower microstructure. The hydrogen evolution reaction (HER) on these macroporous Ni electrodes was evaluated in 30 wt.% KOH solution by means of polarization curves and electrochemical impedance spectroscopy (EIS). Results demonstrate greater apparent activity of the developed electrodes towards HER in comparison with commercial smooth Ni electrode. The 3D porous Ni electrocatalyst obtained from Cu templates synthesized at the lowest current density and the highest electrodeposition time yielded the best electrochemical activity for HER.     

Performance of nickel electrode for alkaline water electrolysis prepared by high pressure cold spray

To promote Ni electrode performance during water splitting, a novel coating process, High pressure cold spray, is applied to prepare electrodes from blended Ni + Al powder. By controlling Al fraction, electrodes are obtained with varied microstructure. SEM and EDX are implemented to check the micromorphology of electrodes. Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) are performed to estimate the effect of Al addition on electrode performance. Resultantly, significant improvement of electrode performance is achieved by increasing the fraction of Al from 10 vol% to 20 vol%. The obtained coatings are found with numerous pores owing to the removal of Al during the activation. By applying electrochemical test, the HER of all samples are dominated by Volmer step, and sample N20A is found with the highest active surface area. Thus, sample N20A exhibits the highest electro-catalytic activity to HER of alkaline water electrolysis.     

Effect of C-felt supported Ni,Co and NiCo catalysts to produce hydrogen

In this study, the carbon felt (C-felt) is used as the catalyst support for Ni, Co and NiCo coatings. Single Ni, Co and binary NiCo coatings are electrochemically deposited on a C-felt. Surface structure of coatings was characterized by cyclic voltammetry (CV), atomic absorption spectroscopy (AAS) and scanning electron microscopy (SEM). The electrocatalytic activity of the coatings for the hydrogen evolution reaction (HER) was studied in 1.00 M KOH solution using cathodic current-potential curves, electrochemical impedance spectroscopy (EIS) and electrolysis techniques. The results show that since carbon felt has fiber and network structure, and this structure is enhanced the hydrogen evolution. Deposition of nickel, and cobalt on C-felt is enhanced the hydrogen production. Furthermore, NiCo catalyst exhibits much higher activity for HER. Its catalytic activity is related to the fiber and network structure of C-felt, porosity and the loaded NiCo can interact with each other and cooperate on improving the HER activity.     

NiMn composite electrodes as cathode material for hydrogen evolution reaction in alkaline solution

NiMn composite catalysts (C/NiMn, C/NiMnZn, C/NiMnZn–PtRu and C/NiMnZn–PtPd) have been prepared on the graphite substrate (C) by electrochemical deposition as electrocatalytic materials for hydrogen evolution reaction (HER). The NiMnZn coatings were etched in a concentrated alkaline solution (30% NaOH) to produce a porous and electrocatalytic surface suitable for the HER. After the leaching process, a low amount of binary PtPd and PtRu were deposited onto the etched NiMnZn deposit in order to improve the catalytic activity for the HER. Surface morphology and composition of the catalysts were analyzed by scanning electron microscopy (SEM) and energy dispersive analysis of X-ray (EDX).     

Hydrogen discharge on electrodeposited Ni–Mn–Fe coatings in 30 w⧸o koh

The hydrogen evolution reaction (HER) has been investigated on Ni–Mn–Fe electrocoated cathodes in 30 w⧸o KOH at 30°C. Ni–Mn–Fe alloys were electrodeposited on mild steel as thin coatings from sulphate baths with ammonium sulphate as additive. The effects of bath composition and deposition current density have been studied. The cathodes were pre-electrolysed at a cathodic current density i_c of 500 mAcm⁻² for 30 min before the kinetic parameters of the HER were determined. Ni–Mn–Fe coatings plated from Ni-rich electrolytes and at very high current densities showed improved activity towards the HER in 30 w⧸o KOH due to significant increase in the exchange current density. Microstructure examinations indicated that the superior electrocatalytic activity, seen in coatings obtained at high deposition current densities, is due to the presence of multi-textures. The coatings, in which formation of nanocrystalline grains and development of voids at grain interfaces occurs, exhibit the maximum electrocatalytic activity towards the HER.     

Amorphous Ni–S–Mn alloy as hydrogen evolution reaction cathode in alkaline medium

Amorphous Ni–S–Mn alloy electrodes were obtained by electrodeposition. The microstructure, surface morphology and composition of the new Ni–S–Mn alloy on the Ni substrate were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS), scanning electron microscopy (SEM) and energy dispersive analysis of X-ray (EDAX). The electrochemical kinetics and mechanism of the hydrogen evolution reaction (HER) of formed electrodes were studied by measurement of the steady-state polarization. Owing to the larger exchange current densities, the lower standard reaction activity energy and a larger surface roughness, the amorphous Ni–S–Mn alloy electrode performs at a higher electrochemical activity with greater stability for the HER in 30 wt% KOH solution at various temperatures than the Ni–S alloy electrode.     

Investigation of noble metal loading CoWZn electrode for HER

It is important to metal deposition on the electrode surface to increase the electrocatalytic activity of the electrodes. CoWZn coated the graphite rod was used to prepare the cathode electrode. Moreover, then Pt and Ru metals were deposited on the electrode surface. These electrodes were named as CoWZnPt and CoWZnRu. Cyclic voltammetry, electrochemical impedance spectroscopy, and potentiodynamic polarization techniques were used for characterization of electrodes in alkaline media. Hydrogen evolution efficiency was determined by accumulated of hydrogen gas. The catalytic activity for hydrogen evolution reaction of CoWZn, CoWZnPt, and CoWZnRu electrodes was compared. It was reported that modification of the CoWZn electrode with low amounts of Ru enhances the HER activity of the electrodes. The enhancement in the hydrogen evolution activity of the electrodes was attributed to the increase in their real surface area and/or a possible synergistic effect between Co, W, Zn and Ru as well as the well-known intrinsic catalytic activity of Ru.