Nanostructured Ni–Co alloy electrodes for both hydrogen and oxygen evolution reaction in alkaline electrolyzer

Ni–Co alloy nanostructured electrodes with high surface area were investigated both as a cathode and anode for an alkaline electrolyzer. Electrodes were obtained by template electrosynthesis at room temperature. The electrolyte composition was tuned in order to obtain different NiCo alloys. The chemical and morphological features of nanostructured electrodes were evaluated by EDS, XRD and SEM analyses. Results show that electrodes with different composition of Ni and Co, made of nanowires well anchored to the substrate, were obtained. For both hydrogen and oxygen evolution reactions, electrochemical and electrocatalytic tests, performed in 30% w/w KOH aqueous solution, were carried out to establishing the best alloy composition. Mid-term tests conducted at a constant current density were also reported. Nanostructured electrodes with a Co atomic composition of 94.73% have the best performances for both hydrogen and oxygen evolution reactions. In particular, with this alloy, a potential of ?0.43 V (RHE) and of 1.615 V (RHE) was measured for hydrogen and oxygen evolution reaction at ?50 mA cm^?2 and at 50 mA cm^?2, respectively, after 6 h of electrolysis. The calculated Tafel's slopes for HER and OER were ?0.105 and 0.088 V/dec, respectively. Furthermore, HER and OER η₁₀ potential values were measured founding ?0.231 V (RHE) and 1.494 V (RHE) respectively.     

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

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

Electrodeposited nickel–zinc alloy nanostructured electrodes for alkaline electrolyzer

Over the last decade, as a consequence of the global decarbonization process, the interest towards green hydrogen production has drastically increased. In particular a substantial research effort has focused on the efficient and affordable production of carbon-free hydrogen production processes. In this context, the development of more efficient electrolyzers with low-cost electrode/electrocatalyst materials can play a key role. This work, investigates the fabrication of electrodes of nickel-zinc alloys with nanowires morphology cathode for alkaline electrolyzers. Electrodes are obtained by the simple method of template electrosynthesis that is also inexpensive and easily scalable. Through the analysis of the morphological and chemical composition of nanowires, it was found that the nanowires composition is dependent on the concentration of two metals in the deposition solution. Electrocatalytic tests were performed in 30% w/w potassium hydroxide aqueous solution at room temperature. In order to study the electrodes stability, mid-term galvanostatic test was also carried out. All electrochemical tests show that nanowires with about 44.4% of zinc have the best performances. Particularly, at ?50 mAcm^?2, these electrodes have an overpotential 50 mV lower than pure Ni nanowire. NiZn nanowires show also a good stability over time without noticeable signs of performance decay.     

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.     

Synthesis of nest-like porous MnCo–P electrocatalyst by electrodeposition on nickel foam for hydrogen evolution reaction

It is very important to develop hydrogen evolution catalyst with high activity and low cost to solve energy crisis. The abundant non-precious metals and phosphides have attracted much attention and are expected to replace platinum catalysts. Herein, we report an approach to prepare nest-like porous MnCo–P electrocatalyst on the nickel foam by two-step electrodeposition. The prepared bimetallic phosphide MnCo–P₃/NF has excellent hydrogen catalytic activity. In the 1 M NaOH solution, the current density of 10 mA cm^?2 required overpotential is only 47 mV, its Tafel slope is 56.4 mV dec^?1, and the higher current density 100 mA cm^?2 required overpotential is only 112 mV. More importantly, the MnCo–P₃/NF catalyst has a long-term stability of electrocatalytic hydrogen evolution. After 24 h catalytic hydrogen evolution test at a constant current density of 20 mA cm^?2, its potential basically does not change. Furthermore, the current density only changes slightly after 1500 cycles of CV test. All these well prove that the prepared MnCo–P₃/NF catalyst has a long-term hydrogen evolution stability. According to performance testing and morphological characterization, the MnCo–P₃/NF has a high hydrogen catalytic activity and stability are due to its larger active area, lower interface charge transfer resistance and stronger mechanical stability. In summary, the study explores a method of preparing bimetallic phosphides as an efficient and stable hydrogen evolution catalyst.     

Partial phosphorization of porous Co–Ni–B for efficient hydrogen evolution electrocatalysis

Design of cost-effective and high-efficient electrocatalysts for hydrogen evolution reaction (HER) is of vital significance for the current renewable energy devices — fuel cells. Herein, we report a facile strategy to prepare partial phosphorization of Co–Ni–B material with porous structure via a water-bath boronizing and subsequent phosphorization process at moderate temperature. The optimal atomic proportion of Co to Ni is investigated via physical and electrochemical characterization. As a result, Co₉–Ni₁–B–P exhibits the best HER activity, which require an lower overpotential of ~192 mV to deliver a current density value of 10 mA cm⁻² and a smaller Tafel slope of 94 mV dec⁻¹ in alkaline media, relative to P-free Co–Ni–B catalysts, Co₉–Ni₁–B–P with other Co: Ni proportion and mono metallic borides The excellent electrocatalytic performance of Co₉–Ni₁–B–P is mainly ascribed to the three-dimensional (3D) porous structure and the coordinate functionalization between the borides and phosphides. This work provides a promising strategy for the exploration of quaternary composites as efficient and cost-effective electrocatalysts for HER.     

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

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

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.     

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.     

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

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

NiCoP–CoP heterostructural nanowires grown on hierarchical Ni foam as a novel electrocatalyst for efficient hydrogen evolution reaction

The design and manufacture of effective non-noble metal catalysts for the H₂ evolution reaction (HER) are urgent for realizing a cost-effective hydrogen production. We report herein on flower-like structures consisting of NiCoP–CoP heterostructural nanowires grown directly on the hierarchically porous nickel framework (NiCoP–CoP/Ni/NF) to achieve a highly efficient HER in alkaline solution (1.0 M KOH). The NiCoP–CoP/Ni/NF is synthesized by electrodeposition of porous Ni layers on Ni foam, followed by simple hydrothermal reaction and phosphorization. For HER, the binder-free NiCoP–CoP/Ni/NF electrode can reach 10 mA cm^?2 current density at a quite low overpotential of 49 mV, because of the combination of porous Ni layers and highly active NiCoP–CoP nanowires. In addition, the NiCoP/CoP heterostructures exhibited remarkable stability under the long-term durability test. This work provides a new strategy that combines electrodeposition and hydrothermal reaction to synthesize effective HER catalysts.     

Electrocatalytic activity for the hydrogen evolution of the electrodeposited Co–Ni–Mo,Co–Ni and Co–Mo alloy coatings

The electrocatalytic activity for the HER of the ternary Co–Ni–Mo and the binary Co–Ni and Co–Mo alloy coatings is investigated in 1 M KOH solution. The surface morphology and the structure of the studied coatings is characterized by SEM and XRD analysis. The electrocatalytic activity for the HER is evaluated using cyclic voltammetry, electrochemical impedance spectroscopy, cathodic polarization and chronopotentiometry techniques. XRD analysis reveals that all studied coatings are composed of the Co hcp structure. However, alloy deposits with Mo is characterized by more nanocrystalline structure. Electrochemical experiments reveal superior electrocatalytic activity of coatings with Mo in comparison to Co–Ni alloy. This is the results of larger real surface area of Co–Mo and Co–Ni–Mo alloys, which is confirmed by the higher surface roughness factors (R_f) calculated based on the EIS results. The ternary alloy coating is characterized by the highest R_f parameter and the highest catalytic activity for the HER.     

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.     

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.     

Electrocatalytic hydrogen evolution on metallic and bimetallic Pd–Co alloy nanoparticles

Increasing world energy demands and crises led to alternative energy production methods, such as fuel cells using hydrogen gas which is the half electrochemical reaction of water splitting process. Herein, we synthesize polyvinylpyrrolidone coated Pd, Co and Pd_xCo_1-x (x: 0.5, 0.12, 0.23, 0.49, 0.55, 0.62) metallic and bimetallic nanoparticles (NPs) via polyol process alternative to Pt-based catalysts for hydrogen evolution reaction (HER). Detailed structural analyses of Pd, Co and Pd_xCo_1-x NPs revealed that fcc-Pd, fcc/hcp-Co and fcc-PdCo NPs crystal structures, and the lattice parameters were calculated as 3.5358 Å for Co NPs and 3.9777 Å for Pd NPs. The average size confirmed below 9 nm via TEM imaging and XPS data confirmed the formation of a bimetallic PdCo structure. Although Pd catalyst is mostly responsible for HER process, Pd₆₂Co₃₈ catalysts reduced the onset potential to about 197 mV and provided greater current density. Although E_a values were slightly higher against the Pt/C (20 wt %) benchmark which is reported as 16 kJ mol⁻¹, PdCo NPs provided considerably reduced activation energy (E_a) values compared to Pd/C catalyst of 31 kJ mol⁻¹. The best onset potential was recorded for Pd₆₂Co₃₈ catalysts for HER activity which is 16 mV higher compared to commercially available Pt/C catalyst.     

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

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

Fluff spherical Co–Ni3S2/NF for enhanced hydrogen evolution

Ni₃S₂ is a kind of HER catalyst electrode with high efficiency and easy preparation. However, due to the weak electrochemical adsorption capacity of water molecules at the Ni site, it is not conducive to the dissociation of water molecules. At the same time, strong sulfur-hydrogen bond is easily formed at the S site, which greatly hinders the desorption and bonding of hydrogen atom to produce hydrogen. Hydrogen evolution performance of Ni₃S₂ in alkaline media needs to be improved. In this paper, fluff spherical Co–Ni₃S₂ was grown in situ on nickel foam by two-step hydrothermal method successfully. By doping cobalt ions, the strong interaction of S–H bond on Ni₃S₂ surface was weakened, the adsorption and dissociation of water molecules were promoted, and the catalyst was exposed to more reactive centers, so as to improve the hydrogen evolution performance of cathodic reduction reaction. Electrochemical test and Transient Photovoltage (TPV) tests show that Co–Ni₃S₂ has fast reaction kinetics and high electron transfer rate, especially it only needs 148 mV low overpotential to reach 10 mA cm^?2 in 1.0 M KOH alkaline electrolyte, which is better than Ni₃S₂/NF (250 mV). In addition, Co–Ni₃S₂ also has excellent electrochemical stability. Density functional theory (DFT) calculations confirm that the optimized adsorption energy enables the catalyst to exhibit excellent HER activity. This work provides useful guidance to construction of effective nickel related HER catalysts.     

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.     

Thermal oxidation–electroreduction modified 3D NiCu for efficient alkaline hydrogen evolution reaction

The preparation of high-efficiency and low-cost electrocatalysts is vital to the development of green hydrogen energy. In this study, 3D NiCu electrodes with hierarchical micro-nano structure was constructed by a simple direct-write 3D printing technology and followed by the treatment of thermal oxidation - electroreduction steps. The composite structure of Cu NWs/Cu₂O and Ni/NiO in the prepared 3D NiCu promotes the dissociation of water and the conversion of hydrogen, and the special micro-nano structure displays a large active surface area. Therefore, the 3D NiCu exhibits a low overpotential of 70 mV to deliver a current density of 10 mA cm^?2. It demonstrates outstanding stability in the hydrogen evolution reaction experiment for 100 h in 1 M KOH. Overall, this research provides a pioneer of modified 3D printing to hydrogen production by water electrolysis.