The stability of hydrogen evolution activity and corrosion behavior of NiCu coatings with long-term electrolysis in alkaline solution

In this study, NiCu composite coating was electrochemically deposited on a copper electrode (Cu/NiCu) and tested for hydrogen evolution reaction (HER) in 1 M KOH solution for long-term electrolysis with the help of cathodic current–potential curves and electrochemical impedance spectroscopy (EIS) techniques. The bulk and surface composition of the coating was determined using atomic absorption spectroscopy (AAS) and energy dispersive X-ray (EDX) analysis. The surface morphology was investigated by scanning electron microscopy (SEM). The effect of electrolysis on the corrosion behavior of the Cu/NiCu electrode was also reported. It was found that the NiCu coating had a compact and porous structure with good time stability. The HER activity of the coating was stable over 120 h electrolysis and the HER mechanism was not modified during the operation. The corrosion tests showed that the corrosion resistance of the Cu/NiCu electrode changed when a cathodic current was applied to the electrolysis system.     

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.     

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.     

The effect of 3D silver nanodome size on hydrogen evolution activity in alkaline solution

Three-dimensional (3D) Ag nanodomes (AgNDs) having different sizes (400, 800, 1200 and 1600 nm) were fabricated using combination of nanosphere lithography and soft lithography. The surface structures of 3D assembled latex particles, nanovoids and metal nanodomes (ND) were examined using scanning electron microscopy (SEM). Their heights and widths analyses were performed with the help of atomic force microscopy (AFM). The effect of diameter of the NDs on their hydrogen evolution activity was examined in 6 M KOH solution at 298 K using electrochemical techniques. Their activities were compared with the activity of bulk Ag electrode. The preparation of 3D-AgNDs having various diameters and examination of their size effects on the water splitting activity have not been studied yet and are being reported firstly. It was found that very well-structured and very uniformly distributed NDs can be fabricated using this procedure. AgNDs exhibit higher hydrogen evolution activity with respect to bulk Ag. Their hydrogen evolution activity depends on their diameters; 1200 nm NDs were the best among them. The current density at ?1.40 V(Ag/AgCl) which is proportional to the rate of hydrogen releasing reaction increases from 0.70 mA cm^?2 to 44.13 mA cm^?2 at this ND electrode with respect to the bulk Ag electrode. At the same 3D-AgNDs electrode and potential, the resistance against the HER reduces from 148.7 Ω cm² to 1.12 Ω cm² (99.6%) by comparing with the bulk Ag electrode. The average surface roughness factors of bulk Ag, 400 nm, 800 nm, 1200 nm and 1600 nm AgNDs are 8, 123, 100, 291 and 176, respectively. The superior hydrogen evolution performance of this electrode is related to its well-structured surface and large real surface area.     

The Ni-deposited carbon felt as substrate for preparation of Pt-modified electrocatalysts: Application for alkaline water electrolysis

A Ni-modified carbon felt (C) electrode (C/Ni) was used as a substrate for preparation of Pt-modified electrode in view of its possible application as electrocatalytic material for the hydrogen evolution activity. The prepared electrode was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and cyclic voltammetry (CV) techniques. The hydrogen evolution activity of the electrode was assessed by cathodic current–potential curves and electrochemical impedance spectroscopy (EIS) techniques. It was found that the modification of Ni-deposited C by loading low amount of Pt could enhance the hydrogen evolution activity of the electrode.     

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.     

Phytic acid-coated titanium as electrocatalyst of hydrogen evolution reaction in alkaline electrolyte

The phytic acid-coated titanium (IP6/Ti) electrode was prepared through a simple drop-drying process, with an aim of improving electrocatalytic activity toward the hydrogen evolution reaction (HER). Scanning electron microscope and X-ray photoelectron spectroscopy showed that the IP6 coated the substrate surface uniformly and completely. Evaluation of the electrode activity was carried out in 1.0 M NaOH by linear polarization, electrochemical impedance spectroscopy (EIS) and chronopotentiometry. The kinetic parameters obtained from Tafel curves reveal that the IP6 coating can enhance the exchange current density of the HER by 489 times compared to the bare Ti, and reduce the HER activation energy by nearly 50%. The EIS data prove that the charge transfer resistance of the HER was considerably reduced due to the IP6 coating, with a decrease in real surface area of the electrode. The catalytic effect of IP6 is due to an improvement in the charge transfer kinetics of the HER. This work indicates that IP6 may be a potent candidate as a catalyst for hydrogen energy production.     

Growth of iron diselenide nanorods on graphene oxide nanosheets as advanced electrocatalyst for hydrogen evolution reaction

Advanced electrocatalysts for the fabrication of sustainable hydrogen from water splitting are innermost to energy research. Herein, we report the growth of iron diselenide (FeSe₂) nanorods on graphene oxide (GO) sheets using two-step process viz., simple hydrothermal reduction and followed by wet chemical process. The orthorhombic phase of FeSe₂ incorporated GO nanosheet was developed as a low-cost and efficient electrocatalyst for hydrogen evolution reaction (HER) by water splitting. The phase purity, crystalline structure, surface morphology and elemental composition of the synthesized samples have been investigated by UV–visible absorption spectroscopy (UV–vis), fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDS). Voltammetry and Tafel polarization methods have been utilized to assess the performance of various weight ratio of GO nanosheet in FeSe₂ nanorods towards H₂ evolution. Detailed electrochemical investigations revealed that the 30% FeSe₂/GO composite showed a tremendous electrocatalytic HER activity in acidic medium with high cathodic current density of 9.68 mA/cm² at η = 250 mV overpotential and with a Tafel slope of 64 mV/dec. The 30% FeSe₂/GO composite offers a high synergistic effect towards HER activity, which is mainly due to high electrochemical active catalytic sites, low charge-transfer resistance and enhanced electrocatalytic performances of H₂ production. The present analysis revealed the possible application of FeSe₂/GO composite as a promising low-cost alternative to platinum based electrocatalysts for H₂ production.     

Accelerating water dissociation kinetic in Co9S8 electrocatalyst by mn/N Co-doping toward efficient alkaline hydrogen evolution

Electrocatalytic hydrogen evolution under alkaline media holds great promising in hydrogen energy production. Transition-metal sulfides (TMSs) are attractive for electrocatalytic alkaline hydrogen evolution, yet their catalytic performance is unsatisfactory owing to the sluggish water dissociation kinetics. Herein, a Mn/N co-doping strategy is proposed to regulate the water dissociation kinetics of Co₉S₈ nanowires array grown on nickel foam thus improve the activity of hydrogen evolution reaction (HER). The optimal Mn/N co-doping Co₉S₈ (Mn–N–Co₉S₈) catalyst achieves low overpotentials of 102 and 238 mV at 10 and 100 mA cm^?2 in the 1 M KOH solution, respectively, remarkably higher than the single-doping Mn–Co₉S₈ and N–Co₉S₈ as well as superior to many reported Co₉S₈-based HER electrocatalysts. Density functional theory (DFT) calculation results confirm that the water dissociation barrier of the Mn–N–Co₉S₈ is reduced significantly owing to the synergistic co-doping of Mn and N, which accounts for the enhanced alkaline HER performance. This study offers an effective strategy to enhance the alkaline HER activity of TMSs by accelerating water dissociation kinetic via the cation and anion co-doping strategy.     

Fabrication of platinum coated nanoporous gold film electrode: A nanostructured ultra low-platinum loading electrocatalyst for hydrogen evolution reaction

The electrolytic hydrogen evolution reaction (HER) on platinum coated nanoporous gold film (PtNPGF) electrode is demonstrated. The deposition of platinum occurred as a spontaneous redox process in which a copper layer, obtained by underpotential deposition, was oxidized by platinum ions, which were reduced and simultaneously deposited. The present method could provide a very low Pt-loading electrode and the results demonstrated that ultra thin Pt coating effected efficiently and behaved as the nanostructured Pt for electrocatalytic hydrogen evolution reaction. The loading of Pt was calculated as 4.2 × 10⁻³ μg cm⁻² for PtNPGF electrode. The current density at −0.4 V and −0.8 V vs. Ag/AgCl was as high as 0.66 A μg⁻¹ Pt and 3 A μg⁻¹ Pt, respectively and the j₀ was evaluated as 0.03 mA cm⁻² or 8 mA μg⁻¹ Pt. The results indicated that increasing electrode area had no catalytic effect, but the nanostructure nature of as-fabricated electrode and submonolayer deposition of copper resulted in electrocatalytic activity for PtNPGF electrode.     

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).     

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 determination of niobium cathode as an efficient electrocatalyst for hydrogen generation in acidic media

Hydrogen gas (H₂) is notified as a renewable energy carrier. It is wanted to discover a low-cost electrocatalyst for the hydrogen evolution reaction (HER) to substitute the high-cost Pt in electrolysis cell. Niobium electrocatalyst nominated to substitute noble materials for electrocatalytic H₂ production and its electrochemical manner was estimated in H₂SO₄ acid of various concentrations utilizing a steady-state polarization and electrochemical impedance spectroscopy (EIS). The influences of acid concentration, cathodic potential and temperature on the H₂ creation were examined. The outcomes display that HER on Nb electrode proceeds by the Volmer-Heyrovsky mechanism. EIS tests, under open circuit and under cathodic polarization, were performed and the fitting has been done utilizing a suggested model for the electrode/electrolyte interface. Apparent activation energies (E_a) were estimated to be ca. 10.5 kJ mol^?1 for the HER on Nb. Thus, Nb is a good electrocatalyst for the cathodic H₂ manufacturing.     

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.     

Self-standing,hybrid three-dimensional-porous MoS2/Ni3S2 foam electrocatalyst for hydrogen evolution reaction in alkaline medium

Self-standing and hybrid MoS₂/Ni₃S₂ foam is fabricated as electrocatalyst for hydrogen evolution reaction (HER) in alkaline medium. The Ni₃S₂ foam with a unique surface morphology results from the sulfurization of Ni foam showing a truncated-hexagonal stacked sheets morphology. A simple dip coating of MoS₂ on the sulfurized Ni foam results in the formation of self-standing and hybrid electrocatalyst. The electrocatalytic HER performance was evaluated using the standard three-electrode setup in the de-aerated 1 M KOH solution. The electrocatalyst shows an overpotential of 190 mV at ?10 mA/cm² with a Tafel slope of 65.6 mV/dec. An increased surface roughness originated from the unique morphology enhances the HER performance of the electrocatalyst. A density functional approach shows that, the hybrid MoS₂/Ni₃S₂ heterostructure synergistically favors the hydrogen adsorption-desorption steps. The hybrid electrocatalyst shows an excellent stability under the HER condition for 12 h without any performance degradation.     

Hydrogen evolution stability of platinum modified graphite electrode

A Platinum-modified alloy coating with high hydrogen evolution reaction (HER) durability activity was prepared by electrodeposition. The durability of this catalyst was determined with electrolysis technique for 120 h. The prepared electrode was characterized by energy dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Long-term electrolysis was carried out in 1 M KOH solution by cathodic current–potential curves and electrochemical impedance spectroscopy (EIS). Experimental result showed that CoZn–Pt coating has a rough structure and presents good stability and high durability. Electrochemical activity increases slightly with increasing electrolysis time. High durability of Pt modified cathode was attributed to the high surface area and synergistic interaction between Co, Zn and Pt.     

Electrocatalytic activity of simple and modified Fe-P electrodeposits for hydrogen evolution from alkaline media

Electrodeposition of Fe-P, Fe-P-Pt and Fe-P-Ce into copper substrates is carried out under galvanostatic conditions. The influence of the current density on the composition of the deposits and the current efficiencies for the electrodeposition processes are determined. Preliminary data indicate that addition of formic acid to the electroplating bath improves the current efficiency for electrodeposition. Electrocatalytic activities of the heat-treated plated materials are investigated by dc polarisation and ac impedance techniques for the hydrogen evolution reaction (HER) in 1 M NaOH solution at 298 K. Steady-state polarisation curves and electrochemical impedance spectroscopy data show that improved catalytic activities for the HER are due to an increase in the effective surface area, a change in surface features upon heat treatment, the partial contribution of the Pt component, and the electrocatalytic synergism with Fe imposed by the Ce co-deposit. Cathodic potentiostatic measurements for medium time operation indicate that the electroplated materials are stable even in moderately aggressive alkaline solutions.     

Defective-MoS2/rGO heterostructures with conductive 1T phase MoS2 for efficient hydrogen evolution reaction

As a two-dimensional material, molybdenum disulfide (MoS₂) exhibits great potential to replace metal platinum-based catalysts for hydrogen evolution reaction (HER). However, poor electrical conductivity and low intrinsic activity of MoS₂ limit its application in electrocatalysis. Herein, we prepare a defective-MoS₂/rGO heterostructures material containing 1T phase MoS₂ and evaluate its HER performance. The experimental results shown that defective-MoS₂/rGO heterostructures exhibits outstanding HER performance with a low overpotential at 154.77 mV affording the current density of 10 mA cm^?2 and small Tafel slope of 56.17 mV dec^?1. The unique HER performance of as-prepared catalyst can be attributed to the presence of 1T phase MoS₂, which has more active sites and higher intrinsic conductivity. While the defects of as-prepared catalyst fully expose the active sites and further improve catalytic activity. Furthermore, the interaction between MoS₂ and rGO heterostructures can accelerate electron transfer kinetics, and effectively ensure that the obtained catalyst displays excellent conductivity and structural stability, so the as-prepared catalyst also exhibits outstanding electrochemical cycling stability. This work provides a feasible and effective method for preparation of defective-MoS₂/rGO heterostructures, which also supplies a new strategy for designing of highly active and conductive catalysts for HER.     

High activity PtPd-WC/C electrocatalyst for hydrogen evolution reaction

Pd modified Pt over a novel support of tungsten carbide nanocrystals (the catalyst denotes as PtPd-WC/C) have been prepared by using an intermittent microwave heating (IMH) method. The as-prepared electrocatalysts are characterized by using the techniques of XRD, SEM, TEM, linear sweeping voltammetry and tested for the hydrogen evolution reaction (HER) in the acidic media. It shows a better performance for the HER on PtPd-WC/C electrocatalyst than that on Pt-WC/C electrocatalyst. In addition, these effects on the catalytic activity by changing environmental temperature and electrolyte concentration were taken into account. Kinetic study shows that the HER on the PtPd-WC/C electrocatalyst gives higher exchange current density in H₂SO₄ solution with high concentration, leading to a lower overpotential and facile kinetics. XRD, SEM and TEM images of PtPd-WC/C show the crystalline features of Pt, Pd and tungsten carbides and indicated the coexistence of these components.     

Ultrashort pulse laser-structured nickel surfaces as hydrogen evolution electrodes for alkaline water electrolysis

In this study, we report on micro- and nanostructured Ni surfaces produced by an ultrashort pulse laser process as cathode materials for the alkaline electrolysis of water. We studied the influence of the laser-induced microstructure and surface morphology as well as a cyclic voltammetric activation process on the electrochemical activity of the hydrogen evolution reaction. Galvanostatic techniques, steady-state polarization curves to attain Tafel parameters and capacitance calculations via electrochemical impedance spectroscopy were used to analyze the electrodes. The analyses reveal that the ultrashort pulse laser process increases the specific surface on formerly flat Ni surfaces. Further, the cyclic voltammetric activation process gives rise to an increased intrinsic activity. Both effects lead to a strongly reduced overpotential value. This work demonstrates that different processes can be combined to dramatically boost the activity of Ni electrodes for the hydrogen evolution reaction.