Electrochemical preparation and characterization of C/Ni–NiIr composite electrodes as novel cathode materials for alkaline water electrolysis

The binary NiIr coatings as novel and effective catalysts were electrochemically prepared on a Ni-modified carbon felt electrode (C/Ni–NiIr) in view of their possible application as cathode materials for the alkaline water electrolysis. The surface morphology and chemical composition of the electrodes were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques. Their hydrogen evolution activity was assessed by electrochemical techniques. It was found that, the preparation of NiIr co-deposits on the Ni-modified C substrate enhances the hydrogen evolution activity. The electrodes have wide space, which is an advantage for diffusion of ions and hydrogen bubbles through inner zones and reduction of diffusion resistance. The high hydrogen evolution activity of the C/Ni–NiIr electrode was mainly attributed to the finer surface structure, high surface area and the higher numbers of the catalytically active centers.     

Electrocatalytic behavior of the Pd-modified electrocatalyst for hydrogen evolution

The hydrogen evolution behavior of C/CoSn, C/CoSnZn and C/CoSnZn–Pd catalysts which were prepared on a graphite substrate (C) by electrochemical deposition, as well as their electrochemical properties in the KOH solutions, have been investigated by the polarization measurements, cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and electrolysis techniques. C/CoSnZn catalyst was etched in caustic to leach out zinc and to produce the Raney-type, porous electrocatalytic surface for hydrogen evolution. In order to further improve the catalytic activity of the C/CoSnZn catalyst for the hydrogen evolution reaction (HER), this catalyst was modified by loading a small amount of Pd. Results showed that the modification of C/CoSnZn catalyst by deposition of a small amount of Pd can render cathode material very active in hydrogen evolution. High catalytic activity of the C/CoSnZn–Pd catalyst depends on the surface porosity, large specific surface area and well known intrinsic catalytic activity of Pd.     

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.     

Fabrication of Mo-modified carbon felt as candidate substrate for electrolysis: Optimization of pH,current and metal amount

Mo was electrochemically deposited over a carbon felt (C) support in order to enhance hydrogen evolution activity of the support and make it a candidate for further modifications. For this aim, the effects of pH of deposition bath solution, deposition current and amount of deposited Mo were studied and optimized. Hydrogen evolution activity of the electrodes was evaluated in 1 M KOH solution with the help of electrochemical techniques. Surface structures of the electrodes were examined by scanning electron microscopy (SEM). It was found that 1 g Mo/g C modified electrode at pH 6 and 50 mA current exhibits the best hydrogen releasing performance. The enhanced current density at this electrode under ?1.60 V(Ag/AgCl) was 59.6% with respect to the bare support, which demonstrates that modifying the support by a thin Mo layer favors the hydrogen evolution reaction (HER) and reduces the energy requirement. The high hydrogen evolution performance of this modified substrate was assigned to its excellent structure, large surface area as well as high intrinsic catalytic activity of Mo. According to experimental findings, the Mo-modified C substrate was suggested for preparation of further modified electrode materials, especially with trace amounts of precious metals.     

Fabrication and characterization of NiCoZn-M (M: Ag, Pd and Pt) electrocatalysts as cathode materials for electrochemical hydrogen production

Ag, Pd and Pt-modified alkaline leached NiCoZn composite coatings were prepared on a copper specimen by electrochemical technique. The chemical composition of layers before and after leaching as well as after noble metal modification was determined by energy dispersive X-ray spectroscopy (EDX). The surface morphologies of the composite coatings were examined with the help of scanning electron microscopy (SEM). The hydrogen evolution activity of the electrodes was studied in 1 M KOH solution. For this purpose, cathodic current-potential curves and electrochemical impedance spectroscopy (EIS) techniques were used. Furthermore, the change of hydrogen evolution activity of the electrodes as a function of operation time in alkaline solution was also investigated. Surface morphologies showed that the composite coatings prepared to have compact and porous surface. EDX analysis confirmed the presence of Ag, Pd and Pt metals over the NiCoZn layer. The co-deposition of nickel, cobalt and zinc on copper surface and subsequently alkaline leaching of zinc rendered cathode material very active in hydrogen evolution. The modification of alkaline leached NiCoZn ternary coating by deposition of small amounts of Ag, Pd and Pt can further enhance the hydrogen evolution performance of this Raney-type electrode when compared to NiCoZn individually. The order of hydrogen evolution activity of catalysts studied is Ni < NiCoZn < NiCoZn-Pd < NiCoZn-Ag < NiCoZn-Pt. The long-term electrolysis tests showed that the Pt-modified electrode has the better time stability than the others. The superiority of Pt-modified catalyst explained by well known intrinsic catalytic activity of Pt.     

Electrochemical performance of porous Ni3Al electrodes for hydrogen evolution reaction

Porous Ni₃Al intermetallic material with a mean pore diameter of around 1 μm was prepared by step sintering Ni and Al powder pressed compacts in vacuum furnace at 900 °C. The electrocatalytic activity of the as-fabricated porous Ni₃Al material as an electrode for hydrogen evolution reaction (HER) in alkaline solutions was investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) techniques. It is found that the onset potential of porous Ni₃Al for HER shifted in the positive direction favoring hydrogen generation with lower overpotential, compared with foam Ni and dense Ni electrodes. Effects of electrolyte concentration and temperature on HER as well as the electrochemical stability in alkaline solution were investigated and the electrochemical activation energy was determined for the porous Ni₃Al. The increased activity for HER was attributed to the high porosity, an increased electrochemical surface area and the nanostructure of porous Ni₃Al electrode. The corrosion tests showed that the corrosion resistance of porous Ni₃Al electrode changed during the immersion process due to the formation of passive film layers.     

NiGa modified carbon-felt cathode for hydrogen production

In this study, known electrocatalytic active metal nickel and low amount of gallium were electrodeposited on carbon felt electrode for hydrogen evolution reaction in alkali medium. Morphological and structural analyses of prepared electrodes were determined by scanning electron microscopy and energy dispersive X-ray spectroscopy. The electrocatalytic activity of obtained electrodes for hydrogen evolution reaction was determined with cathodic polarization curves, electrochemical impedance spectroscopy, discharge potential measurements, hydrogen volume measurements at constant potential and durability tests. It was found that the electrodeposition of low amount of gallium over the nickel coated carbon felt electrode increases the hydrogen evolution reaction activity and decreases the overpotential for hydrogen region. The electrocatalytic activity of nickel and gallium deposited on carbon felt electrode was explained with active sites of surface and synergistic effect of nickel and gallium created by high surface area of carbon felt.     

The stability of NiCoZn electrocatalyst for hydrogen evolution activity in alkaline solution during long-term electrolysis

The long-term stability of NiCoZn coating for hydrogen evolution reaction (HER) was investigated in 1 M KOH solution under 100 mA cm⁻² current density at room temperature. The effect of electrolysis on the corrosion behavior of NiCoZn coating was also studied. The alloy prepared on a copper electrode (Cu/NiCoZn) was etched in a concentrated alkaline solution (30% NaOH) to produce a porous and electrocatalytic surface suitable for use in the HER. The bulk and surface compositions of coating before and after alkaline leaching were determined by atomic absorption spectroscopy (AAS) and energy dispersive X-ray (EDX) analysis. The surface morphologies of freshly prepared and aged electrodes were investigated by scanning electron microscopy (SEM). Their catalytic activity towards the HER was assessed by recording cathodic current–potential curves and electrochemical impedance spectroscopy (EIS) techniques. It was found that the NiCoZn coating has a compact and porous structure. The long-term operation at 100 mA cm⁻² current density showed that the electrochemical activity of Cu/NiCoZn electrode increased slightly with increasing electrolysis time. The activation of electrode related to the removal of any existing corrosion products and accumulations from the pores and formation of cracks during hydrogen gas evolution. The corrosion tests showed that the corrosion resistance of Cu/NiCoZn electrode changed after electrolysis.     

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.     

Synthesis and electrocatalytic hydrogen evolution performance of Ni–Mo–Cu alloy coating electrode

Ni–Mo–Cu alloy coating electrode was prepared on copper substrate by constant current electrodeposition and characterized by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The electrochemical characterization for hydrogen evolution reaction (HER) was investigated by cyclic voltammetry (CV) curves, linear sweep voltammetry (LSV) curves and electrochemical impedance spectroscopy (EIS) techniques. Parameters affecting the electrocatalytic activity for the HER are systematically investigated. Results show the Ni–Mo–Cu coating by the introduction of Cu has a rough and cauliflower-like structure and presents a most efficient activity for HER in comparison with binary Ni–Mo electrode. Its remarkably enhanced catalytic activity is attributed to the high surface area as well as synergistic interaction between Ni, Mo and Cu.     

Assessment of the roughness factor effect and the intrinsic catalytic activity for hydrogen evolution reaction on Ni-based electrodeposits

The hydrogen evolution reaction (HER) was studied in 30 wt.% KOH solution at temperatures ranging between 30 and 80 °C on three type of electrodes: (i) rough pure Ni electrodeposits, obtained by applying a large current density; (ii) smooth NiCo electrodeposits; (iii) smooth commercial Ni electrodes. By using steady-state polarization curves and electrochemical impedance spectroscopy (EIS) the surface roughness factor and the intrinsic activities of the catalytic layers were determined. These techniques also permitted us to determine the mechanism and kinetics of the HER on the investigated catalysts. Different AC models were tested and the appropriate one was selected. The overall experimental data indicated that the rough/porous Ni electrode yields the highest electrocatalytic activity in the HER. Nevertheless, when the effect of the surface roughness was taken into consideration, it was demonstrated that alloying Ni with Co results in an increased electrocatalytic activity in the HER when comparing to pure Ni. This is due to an improved intrinsic activity of the material, which was explained on the basis of the synergism among the catalytic properties of Ni (low hydrogen overpotential) and of Co (high hydrogen adsorption).     

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.     

Hydrogen evolution on nickel electrode in synthetic tap water - alkaline solution

The effect of tap water contaminants on the kinetics of the hydrogen evolution reaction on a nickel electrode in 1 mol dm⁻³ KOH was investigated by galvanostatic polarization and electrochemical impedance spectroscopy techniques. It was found that the tap water contaminants lead to an increase in the overpotential of the hydrogen evolution reaction, especially at low temperatures. The combination of electrochemical techniques, as well as physicochemicals such as SEM and EDAX ones, confirmed that the contaminants are specifically adsorbed and blocked the available electrode surface for the reaction. It was concluded that they do not participate in an electrochemical reaction in the potential region where HER occurs. Besides the short term negative impact on the rate of hydrogen evolution, a 55 h test revealed that the overpotential shows a steady increase over time in presence of tap water contaminants, while in absence of these contaminants the overpotential is constant.     

Hydrogen evolution reaction enhanced by water-soluble metallopyridinoporphyrazine complex adsorbed on highly oriented pyrolytic graphite

The ultrathin (∼2 nm) film of N,N',N'′,N′″-tetramethyltetra-3,4-pyridino-porphyrazinato-cobalt(II) complex adsorbed on the basal plane of highly oriented pyrolytic graphite (HOPG/Co(I)Tmtppa) was used as a mediator for electrocatalytic hydrogen evolution reaction (HER) in a wide range of pH. The Co(I)Tmtppa film was characterized by in-situ backscattering spectroscopy, atomic force microscopy and cyclic voltammetry. Electrocatalytic measurements of HOPG/Co(I)Tmtppa electrode using voltammetric techniques showed up to 60-fold increase of current density and overpotential decreased by 300 mV, compared to the bare HOPG electrode at pH 11 and confirmed very good stability with only 8% deviation over 1000 cycles. The Tafel analysis indicated the Volmer-Heyrovsky mechanism of hydrogen evolution reaction with hydrogen adsorption rate-determining step at all pH values.     

Preparation,characterization and hydrogen production performance of MoPd deposited carbon felt/Mo electrodes

Mo-coated carbon felt (C) supporting material modified by electrochemical deposition of trace amounts of MoPd binary composites having various metal ratios and characterized using various techniques. To our best knowledge, these materials is being reported firstly. The hydrogen evolution activity of the electrodes tested in 1 M KOH solution using electrochemical techniques. It shown that MoPd modified electrodes have large surface area, which is very beneficial for the rate of hydrogen evolution reaction (HER). Pd and Mo metals almost homogeneously distributes over the surface and no local aggregations are appeared. The loading of MoPd binary deposits over the Mo-coated C supporting material enhances the rate of the HER more and more when compared to the base substrate. The hydrogen evolution performance of the composites is depending on the metal ratios. The enhanced current density at the C/Mo-Mo₅₀Pd₅₀ electrode at ?1.60 V(Ag/AgCl) is 79.1% with respect to the C felt and 48.1% with respect to the C/Mo modified supporting material. The reduction in resistance related to hydrogen gas releasing at 100 mV overpotential was 97.2% and 58.6% with respect to bare C felt and C/Mo supporting material. The high hydrogen releasing performance of the PdMo-modified electrocatalysts related to intrinsic catalytic activities of Pd and Mo, a possible synergism between these metals and enhanced real surface area of the electrode. The C/Mo-Mo₅₀Pd₅₀ electrode has excellent electrochemical and physical stability during the long time electrolysis. Therefore, it is expected that the procedure applied here contribute to literature since the modifying C support by an active metal provides activation of electrocatalysts. Due to superior properties, we can suggest C/Mo-Mo₅₀Pd₅₀ electrode as promising cathode material for industrial water electrolysis which can reduces the energy input.     

Fabrication,characterization and application of three-dimensional copper nanodomes as efficient cathodes for hydrogen production

In this study, three-dimensional (3D) copper nanodomes (Cu-NDs) were fabricated by a combined method of nanosphere-soft lithography, electrochemical and physical vapor deposition (PVD) methods. The 3D Cu-NDs were characterized using surface characterization techniques. The hydrogen production performance and time-stability of the electrodes were examined in a concentrated alkaline solution (6 M KOH) using various electrochemical techniques. The experimental results showed that very uniformly and closely packed Cu-NDs were prepared by the combined methods. The hydrogen generation activity of the 3D Cu-NDs was significantly improved with respect to bulk Cu. Fabricating Cu-NDs does not effect of the hydrogen evolution mechanism and the reaction is activation controlled. The water splitting reaction starts at lower potentials and larger current densities at a fixed potential were appeared at the Cu-NDs electrode. The average reduction in the charge transfer resistance related to the reaction of hydrogen gas evolution is 91.9% at the Cu-NDs electrode with respect to the bulk Cu. The enhanced activity of the nanostructures was related to enlarging real surface area and available more active centers at the Cu-NDs surface. The Cu-NDs electrode has excellent time stability in alkaline solution.     

Gold‐supported activated NiZn coatings: hydrogen evolution and corrosion studies

Gold‐supported Raney‐type NiZn coatings were prepared on a thin Ni film‐modified copper substrate (Cu/Ni/NiZn‐Au). The hydrogen evolution activity, time stability and corrosion behaviour of the electrode was investigated in 1 M KOH solution by electrochemical, microscopic and spectroscopic technique. It was found that Au‐modified activated coatings exhibits good hydrogen evolution activity, electrochemical and physical stability as well as corrosion resistance. The enhanced hydrogen evolution activity of the Au‐modified electrode was related to the larger available surface area and/or a possible synergistic effect between the metals. Copyright © 2017 John Wiley & Sons, Ltd.     

Pt/Fe-NF electrode with high double-layer capacitance for efficient hydrogen evolution reaction in alkaline media

The electrode with high catalytic activity, low hydrogen overpotential and low cost is desired for hydrogen evolution reaction (HER) via electrocatalytic water splitting. In this study, Pt/Fe-Ni foam (Pt/Fe-NF) electrode was synthesized via cathodic electrodeposition followed by impregnation deposition. Physical and electrochemical properties of Pt/Fe-NF, NF and Pt/NF electrodes were characterized by various techniques. The Pt/Fe-NF electrode exhibited better electrochemical activity for HER under alkaline condition than those of Pt/NF and NF electrodes, owing to the introduction of zero valences Pt and Fe onto the NF, and synergetic effect resulted from the formation of Fe-Ni alloy. Furthermore, Pt/Fe-NF electrode showed extremely high double-layer capacitance (69.1 mFcm^?2), suggesting high active sites for the Pt/Fe-NF. Tafel slope of Pt/Fe-NF was 59.9 mV dec^?1, indicating that the Volmer-Heyrovsky HER mechanism was the rate-limiting step. The Pt/Fe-NF electrode with great electrocatalytic activity is a promising electro-catalyst for industrial hydrogen production from alkaline electrolyte.     

Preparation,characterization and application of alkaline leached CuNiZn ternary coatings for long-term electrolysis in alkaline solution

The NiCuZn ternary coating was electrochemically deposited on a copper electrode. Then, it was etched in a concentrated alkaline solution (30% NaOH) to produce a porous and electrocatalytic surface suitable for use in the hydrogen evolution reaction (HER). The surface composition of coating before and after alkaline leaching was determined by energy dispersive X-ray (EDX) analysis. The surface morphologies were investigated by scanning electron microscopy (SEM). The long-term stability of electrode prepared for alkaline water electrolysis was investigated in 1 M KOH solution with the help of cathodic current-potential curves and electrochemical impedance spectroscopy (EIS) techniques. It was found that, the NiCuZn coating has a compact and porous structure with good physical stability. Alkaline leaching process further improved the activity of NiCuZn coating in comparison with binary NiCu deposit for the HER. The long-term operation at −100 mA cm⁻² showed good electrochemical stability over 120 h.     

Nickel nanocones as efficient and stable catalyst for electrochemical hydrogen evolution reaction

In this work, nickel nanocones (NNCs) were fabricated by single-step electrodeposition method. The NNCs were used as hydrogen evolution electrode and their electrocatalytic activity was compared with pure nickel film. Linear Sweep Voltammetry (LSV), Tafel polarization, Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV) and chronopotentiometry in 1 M KOH were used for study of the electrocatalytic activity for hydrogen evolution reaction (HER). The active surface area was increased by formation of NNCs and hence, the electrocatalytic activity of nickel electrode was improved. Results indicate that the current density corresponding to the amount of evolved hydrogen of NNCs is five times more than pure nickel film formed in the Watts bath.