Well-dispersed Pt nanodots interfaced with Ni(OH)2 on anodized nickel foam for efficient hydrogen evolution reaction

Hindered by price and scarcity, the exploitation of supported Pt-based electrocatalysts with Pt single atoms or Pt nanoclusters is an alternative way to decrease the dosage of Pt and improve the electrocatalytic performance for hydrogen evolution reaction (HER) of water splitting. The anodization technology is used to modify the surface of nickel foam (NF) to form the porous NiF₂ network structure. Then Pt nanodots interfaced with Ni(OH)₂ (Pt/Ni(OH)₂) hybrid on the anodized NF has been in-situ synthesized by a simple hydrothermal decomposition method. Results show that Pt nanodots on the substrate have good dispersion with the average size of 3 nm, and the Pt loading is only 0.229 mg cm⁻². The prepared electrode exhibits the low overpotentials of 25.9 mV and 211 mV at the current densities of 10 and 100 mA cm⁻², respectively, a small Tafel slope of 37.6 mV dec⁻¹, and the excellent durability for HER. The porous network nanostructure of Pt/Ni(OH)₂ hybrid, the large electrochemical surface area, the fast facilitated electron transport capability, and the firm adhesion of Pt nanodots with the anodized NF substrate contribute to the remarkable performance towards HER.     

Needle-like CoP/rGO growth on nickel foam as an efficient electrocatalyst for hydrogen evolution reaction

In this work, CoP/NF is synthesized at different temperature (250 °C, 300 °C, 350 °C) (denoted as CoP/NF-T, T = 250, 300, 350). Then, CoP/NF-300 with the best performance towards hydrogen evolution reaction (HER), is used to synthesize compounds with different ratio of reduced graphene oxide (rGO) (CoP/rGO/NF-X, X (quality ratio of rGO/CoP) = 1,3,5). In terms of morphology, under the synergistic effect of rGO, uniform and dense CoP provides the possibility to increase the electrochemical area. While CoP/rGO/NF-3 shows the minimum overpotential of 136 mV to drive 50 mA/cm, and the smallest Tafel slope 135 mV/dec among as-synthesized materials. Furthermore, CoP/rGO/NF-3 has good stability during at least 25 h. These result can be construed as the large electrochemical active area, high conductivity and long-time stability.     

In situ electro-oxidation modulation of Ru(OH)x/Ag supported on nickel foam for efficient hydrogen evolution reaction in alkaline media

Transition metal hydroxides for hydrogen evolution reaction (HER) usually have been limited by poor intrinsic activity and weak conductivity. In our work, in situ electro-oxidation as an effective way has been used to modulate the electronic states of active sites for ruthenium hydroxides, which provides obviously enhanced activity for HER in alkaline media. Ag-modified nickel foam (NF) as substrate can provide the excellent conductivity to improve the charge transfer rate of Ru(OH)_x/Ag/NF. In situ electro-oxidation process has been conducted for Ru(OH)_x/Ag/NF through OER measurements in alkaline media, which results in the formation of more Ru (IV) as higher actives sites for HER. Compared to Ru(OH)_x/NF, X-ray photoelectron spectroscopy (XPS) and polarization curves prove that Ag doping in Ru(OH)_x/Ag/NF may contribute to the oxidization of ruthenium from Ru (III) to Ru (IV) during in situ electro-oxidation. The obtained Ru(OH)_x/Ag/NF exhibits Pt-like HER activity with a very low overpotential of 103.2 mV to drive 100 mA cm⁻² in 1.0 M KOH. The excellent stability of Ru(OH)_x/Ag/NF has also been demonstrated. Therefore, our work provides a new strategy by modulating valence state of active sites for transition metal hydroxides for efficient HER.     

Effect of carbon coating on Cu electrodes for hydrogen production by water splitting

In recent years, fossil fuel depletion has been increasing, which leads to environmental issues. Hydrogen energy is considered a promising renewable energy to replace fossil fuels because it is a sustainable, clean, and green energy source. Among hydrogen production methods, water splitting has the highest reliability and is used the most often. Platinum is normally used as water splitting catalyst and an electrode. However, there has been much effort to replace it as such owing to its high cost. Copper (Cu) is not used as water splitting catalyst or an electrode, despite its high current density, because of its corrosive properties. In this study, carbon was coated onto a Cu substrate and a hydrogen production experiment was carried out with 0.1 M Na₂SO₄ and 0.1 M H₂SO₄ electrolytes. As a result, the carbon coating decreased oxidation rate of the Cu electrode and effected stability in short-term hydrogen evolution experiment. This indicates the possibility of carbon-Cu electrode with other catalytic materials.     

Coupling NixSy-Ni2P heterostructure nanoarrays on Ni foam as environmentally friendly electrocatalyst for overall water splitting

The development of efficient, cheap and stable electrodes is the key to achieve the industrialization of hydrogen production from electrochemical water splitting. In this paper, Ni_xS_y-Ni₂P mixtures on Ni foam (Ni_xS_y-Ni₂P/NF) were synthesized by hydrothermal process followed by sulfurization and phosphorization approach. The combination of Ni_xS_y and Ni₂P exposes a large number of active sites, thus greatly improving the catalytic activity of the material. As expected, the Ni_xS_y-Ni₂P/NF material exhibits ultra-small overpotentials of 211 and 320 mV for water oxidation reaction at the current densities of 10 and 100 mA/cm², respectively. What is noteworthy is that the material also present superior hydrogen evolution reaction properties (122 mV@10 mA cm^?2). Moreover, when the material is acted as a bifunction electrode to drive the overall water splitting, only a cell voltage of 1.54 V is required to drive a current density of 10 mA/cm², which is one of the superior catalytic properties reported up to now. Experimental results show that the good electrochemistry performance of the Ni_xS_y-Ni₂P/NF material is attributed to the improved charge transfer rate, exposure of more active site and superior electrical conductivity. This work provides an effective way to explore environmentally friendly catalysts based on transition metal sulfide and phosphide.     

Porous flower-like nickel nitride as highly efficient bifunctional electrocatalysts for less energy-intensive hydrogen evolution and urea oxidation

Finding a suitable replacement for the high potential of anodic water electrolysis (oxygen evolution reaction (OER)) is significant for hydrogen energy storage and conversion. In this work, a simple and scalable method synthesizes a structurally unique Ni₃N nanoarray on Ni foam, Ni₃N-350/NF, that provides efficient electrocatalysis for the urea oxidation reaction (UOR) that transports 10 mA cm⁻² at a low potential of 1.34 V. In addition, Ni₃N-350/NF exhibits electro-defense electrocatalytic performance for hydrogen evolution reaction, which provides a low overpotential of 128 mV at 10 mA cm⁻². As proof of concept, all-water-urea electrolysis measurement is carried out in 1 M KOH with 0.5 M Urea with Ni₃N-350/NF as cathode and anode respectively. Ni₃N-350/NF||Ni₃N-350/NF electrode can provide 100 mA cm⁻² at a voltage of only 1.51 V, 160 mV less than that of water electrolysis, which proves its commercial viability in energy-saving hydrogen production.     

Cathodic hydrogen recovery and methane conversion using Pt coating 3D nickel foam instead of Pt-carbon cloth in microbial electrolysis cells

A cheap but efficient electrode material is required to explore and apply to microbial electrolysis cell (MEC) with high hydrogen evolution reaction (HER) efficiency and low over-potential loss. Pt coating carbon cloth (Pt/CC) was one of the most efficient catalyst for hydrogen production in current lab research, but it is difficult to be applied in practice because of expensive cost and week strength from the base material (carbon cloth). Thus a cheap and effective supporting base material is worth to evaluate on hydrogen recovery and loss to methane for the MEC future application. In this study, nickel foam (NF) was used as an alternative to expensive carbon cloth, and NF coated with Pt (Pt/NF) was applied and evaluated through catalytic performance, hydrogen production efficiency and economic assessment in comparison with Pt/CC. The Pt/NF showed a competitive HER performance to Pt/CC. The highest hydrogen yield was reached 0.71 ± 0.03 m³/m³·d by Pt/NF under 0.8 V, which exceeded 6%, 10% over Pt/CC and NF, respectively. The energy efficiency relative to the electrical energy input was 127% for Pt/NF and 123%, 110% for Pt/CC and NF, respectively. For fifteen cycles, the methane content of Pt/NF got the lowest due to its higher hydrogen evolution activity. The economic analysis showed a 56% reduction when using Pt/NF as supporting base in place of carbon cloth to achieve similar performance. The linear sweep voltammetry (LSV) showed the possibility to further reduce input voltage in a long term operation.     

Mixed-dimensional niobium disulfide-graphene foam heterostructures as an efficient catalyst for hydrogen production

Besides developing a large number of catalysts for hydrogen evolution reaction (HER) in alkaline electrolytes, its conversion efficiency remained low. Herein, we have developed mixed-dimensional heterostructures of niobium disulfide (NbS₂) with graphene foam grown on nickel foam (NbS₂-Gr-NF). The strong lateral fusion results in activating the catalytic sites of NbS₂, the three-dimensional substrate provides easy access of electrolyte to active sites and increased electrochemically active surface area, while enhanced conductivity provides faster transfer of electrons to and from active sites. Therefore, NbS₂-Gr-NF heterostructures resulted in an exceptionally high current density of 500 mA cm⁻² at a very low overpotential of 306 mV in 1 M KOH solution and even can achieve the current density values of 914 mAcm⁻² at 338 mV only at a slight increase in overpotential (32 mV). Moreover, a Tafel value of ~72 mV dec⁻¹ confirms that as-developed heterostructure provides fast reaction kinetics where the reaction is mainly controlled by the Volmer step. Achieving such high current density at a faster rate with high stability makes NbS₂-Gr-NF heterostructures a potential candidate for water-splitting, especially in alkaline electrolytes.     

The dynamics of the nickel foam formation and its effect on the catalytic properties toward hydrogen evolution reaction

Porous nickel deposits were obtained by electrodeposition via dynamic hydrogen bubble template in a galvanostatic mode at a current density of 0.3, 0.6, 0.9 and 1.2 A·cm⁻². Change of nickel foam morphology (dendrite particles, pore number and their sizes) with the applied current density was analyzed. It was found that at low hydrogen evolution rate, a gradual formation of a porous structure occurs, while at high ones, the formation of the template structure ends in the first minutes of electrolysis. It is shown that the log-normal distribution can be used to describe the formation of a hydrogen template as a system of nickel foam macropores. The catalytic activity of nickel foams toward hydrogen evolution was analyzed in an alkali solution. The Tafel slope for the obtained foams is in the range of 126-107 mV·dec⁻¹. Nickel foams obtained at 1.2 A·cm⁻² are the best candidates for hydrogen evolution electrodes due to their stable structure, providing maximum access of reacting particles to the inner surface of the electrode.     

Controlled synthesis of CrxPy-a/ComPn-b nanoarray on nickel foam as efficient electrocatalyst for overall urea splitting

Developing highly efficient bifunctional urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) catalysts for urea splitting to hydrogen are one of the strategies to cope with the energy crisis. Here, a series of Cr_xP_y-a/Co_mP_n-b composites were synthesized on Ni foam through hydrothermal and low-temperature phosphorization process for the first time. It is worth noting that Cr_xP_y-1/Co_mP_n-3@NF exhibited excellent UOR performance (1.331 V at 100 mA cm^?2) and HER performance (0.299 V at 100 mA cm^?2) in an electrolyte of 1 M KOH and 0.5 M urea due to the synergistic effect of Cr–Co. The Cr_xP_y-1/Co_mP_n-3@NF||Cr_xP_y-1/Co_mP_n-3@NF two-electrode system call for only 1.52 V to provide current density of 10 mA cm^?2, which is one of the best electrochemistry performances reported up to now. Experimental analysis show that the promoted electrochemistry performances is assigned to faster charge transfer rate, the exposure of more reaction site and better properties of metals. Density Functional theory (DFT) results demonstrate that the presence of the Co_mP_n material accelerates the kinetics of hydrogen production and the Cr_xP_y material improves the properties of metals for the electrode. The work provides a new idea to develop the environmentally friendly and low cost overall urea splitting catalyst with transition metals instead of noble metals.     

Straightforward preparation of nickel selenide nanosheets supported on nickel foam as a highly efficient electrocatalyst for oxygen evolution reaction

The development of economical, durable, and efficient oxygen evolution reaction (OER) electrocatalysts is essential for large-scale industrial water electrolysis. Here, a straightforward strategy is proposed to synthesize a series of nickel selenide nanosheets supported on nickel foam (NiSe₂/NF) materials by directly selenizing nickel foam substrates at different temperatures under an inert atmosphere. When evaluated as electrocatalysts in OER, the optimal self-supported NiSe₂/NF-350 shows an excellent performance in 1.0 M KOH medium with an overpotential of 458 mV at 100 mA cm^?2, a small Tafel slope of 45.8 mV dec^?1, and a long-term stability for 36 h. Furthermore, the structural and compositional preservation for NiSe₂/NF-350 after stability test was also verified by various characterizations.     

Hydrothermally synthesized nickel molybdenum selenide composites as cost-effective and efficient trifunctional electrocatalysts for water splitting reactions

The development of efficient, cost-effective routes to prepare non-platinum-based electrocatalysts is a significant scientific challenge in water-splitting systems. A multifunctional electrocatalyst for the hydrogen evolution, oxygen evolution, and oxygen reduction reactions (HER/OER/ORR) involved in the water-splitting process was fabricated using a simple and eco-friendly strategy. The present study involves the simple synthesis of nanostructured nickel selenide (NiSe) via a hydrothermal method. The different phases of nickel selenide and their dependency on the precursor concentration were analyzed using X-ray diffraction (XRD). The morphologies of coral-like structured pure and Mo-doped NiSe (Ni_1-xMo_xSe) samples were investigated systematically using scanning electron microscopy (SEM). The as-prepared Ni_0.5Mo_0.5Se material showed an enhanced electrochemical activity of 1.57 V @ 10 mA/cm² for OER and 0.19 V @ 10 mA/cm² to HER, and follows the Volmer-Heyrovsky for HER mechanism. In addition, the electrocatalyst exhibits a large electrochemical surface area and high stability. Therefore, the hydrothermally synthesized Ni_1–xMo_xSe has been proven to be a perfect platinum-free trifunctional electrocatalyst for water splitting process.     

Facile synthesis of binary NiCoS nanorods supported on nickel foam as efficient electrocatalysts for oxygen evolution reaction

A facile two-step method has been applied to synthesize novel binary metal NiCoS nanorods supported on nickel foam (NF) as electrocatalysts for oxygen evolution reaction (OER). Firstly, electrodeposition process is conducted to fabricate binary Ni-Co hydroxides on NF (NiCo/NF). Then, a hydrothermal sulfuration of NiCo/NF has been adopted to prepare NiCoS nanorods arrays uniformly grown on the surface of NF (NiCoS/NF). XRD indicates that NiCoS/NF has mixed crystal phases of Ni₃S₂, CoS and Co₉S₈. SEM images display the uniform NiCoS nanorods composed of many vertical nanosheets on the surface, implying more exposed active sites. OER measurements demonstrate that NiCoS/NF has better activity with an overpotential of 370 mV to reach 100 mA cm^?2 than NiCo/NF and CoS_x/NF. Electrochemical impedance spectroscopy (EIS) tests confirm the faster charge-transfer rate of NiCoS/NF and smaller Tafel slope derived from binary NiCoS, implying the excellent electrocatalytic performances of binary metal sulfides.     

Preparation and characterization of active and cost-effective nickel/platinum electrocatalysts for hydrogen evolution electrocatalysis

Designing active and cost-effective electrocatalysts is important in the field of energy economics, particularly for hydrogen production, which is at the core of many energy conversion technologies. This investigation reports on the preparation of nickel-based materials targeting electrocatalytic hydrogen evolution in either alkali or physiological solutions. Nickel-based metallic nanoparticles were synthesized via the bromide anion exchange method, and their performance was compared with the performances of a homemade nickel mesh and a high-purity nickel foil. The Ni₉₉Pt₀₁/C electrocatalyst performed the best in terms of overpotential and generated current density, notably in physiological conditions. In addition, the homemade electroformed nickel mesh behaved as well as a commercial high-purity nickel foil in alkaline medium and even better in buffered solution at pH 7. Both materials are environmentally friendly and economically viable candidates for technologies that require large cathode materials, especially when hydrogen production in neutral electrolytes is sought.     

Exaggerated capacitance using electrochemically active nickel foam as current collector in electrochemical measurement

In the past decades, nickel and cobalt oxide/hydroxide materials have been investigated intensively for supercapacitor applications. Some works report very high specific capacitance values, up to 3152 F g⁻¹, for these materials. By contrast, some other works report quite modest capacitance values, up to 380 F g⁻¹ for the same materials prepared using same strategy. It is found that most works reporting very high capacitance value applied nickel foam as current collector. In this paper, surface chemistry and electrochemical properties of nickel foam are investigated by XPS analysis, cyclic voltammetry and galvanostatic charge-discharge measurement. The results show that using nickel foam as current collector can bring about substantial errors to the specific capacitance values of electrode materials, especially when small amount of electrode active material is used in the measurement. It is suggested that an electrochemically inert current collector such as Ti or Pt film should be used for testing electrochemical properties of nickel and cobalt oxide/hydroxide positive electrode materials.     

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.     

Assessment of the effect of electrophoretic deposition parameters on hydrogen storage performance of graphene oxide layer applied on nickel foam

In this study, the hydrogen storage capacity of the graphene oxide layer was studied electrochemically. The graphene oxide was synthesized by modified Hummers' method and applied on the nickel foam by electrophoretic deposition (EPD) method at different potentials (20 and 60 V) and times (20 and 60 min) to determine the effect of applied potential and time of deposition on the hydrogen adsorption performance. The hydrogen adsorption tests including charge-discharge test, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were conducted in 6 M KOH solution and at room temperature. Based on the achieved CV curves, the graphene oxide (GO) layer achieved at 60 V within 20 min has a higher electrochemical hydrogen adsorption capability compared to other obtained samples. The calculated hydrogen storage capacity is obtained 50.9 mA. h. g^?1. The rosette flower like morphology of the obtained GO layers at optimum condition, has an impressive effect on the improving electrochemical hydrogen adsorption based on morphology study by field emission scanning electron microscopy.     

Carbon supported nickel phosphide as efficient electrocatalyst for hydrogen and oxygen evolution reactions

Hydrogen production through water splitting is an efficient and green technology for fulfilling future energy demands. Carbon nanotubes (CNT) supported Ni₂P has been synthesized through a simpler hydrothermal method. Ni₂P/CNT has been employed as efficient electrocatalysts for hydrogen and oxygen evolution reactions in acidic and alkaline media respectively. The electrocatalyst has exhibited low overpotential of 137 and 360 mV for hydrogen and oxygen evolution reactions respectively at 10 mA cm^?2. Lower Tafel slopes, improved electrochemical active surface area, enhanced stability have also been observed. Advantages of carbon support in terms of activity and stability have been described by comparing with unsupported electrocatalyst.     

Interlaced rosette-like MoS2/Ni3S2/NiFe-LDH grown on nickel foam: A bifunctional electrocatalyst for hydrogen production by urea-assisted electrolysis

In targeting the most important energy and environmental issues in current society, the development of low-cost, bifunctional electrocatalysts for urea-assisted electrocatalytic hydrogen (H₂) production is an urgent and challenging task. In this work, interlaced rosette-like MoS₂/Ni₃S₂/NiFe-layered double hydroxide/nickel foam (LDH/NF) is successfully synthesized by a two-step hydrothermal reaction. Due to its unique interlaced heterostructure, MoS₂/Ni₃S₂/NiFe-LDH/NF exhibits excellent bifunctional catalytic activity towards the urea oxidation reaction (UOR) and the hydrogen evolution reaction (HER) in 1.0 M KOH with 0.5 M urea. In a concurrent two-electrode electrolyser (MoS₂/Ni₃S₂/NiFe-LDH/NF(+,-)), only voltage of 1.343 V is required to reach 50 mA cm⁻², which is 216 mV lower than for pure water splitting. Furthermore, after 16 h of urea electrolysis in 1.0 M KOH with 0.5 M urea, the current density remains at 98% of the original value. Thus, the catalyst is not only favorable for H₂ production, but also has great significance for the problem of urea-rich wastewater treatment.     

Amorphous CoFeB on nickel foam as a high efficient electrocatalyst for hydrogen evolution reaction

The development of high-performance, low cost and earth abundant catalysts for hydrogen evolution reaction (HER) is desired. This work presents amorphous CoFeB supported on nickel foam (NF), prepared by a facial chemical reduction method, as an active catalyst for HER in alkaline solution. Structure characterization indicated that with the incorporation of Fe atom, CoFeB catalysts exhibit similar petal-like granular morphology as CoB. The optimal CoFeB/NF-0.15 catalyst exhibits Brunauer-Emmett-Teller (BET) surface area of 27.4 m² g^?1, nearly two times larger than 13.2 m² g^?1 for CoB, suggesting higher specific surface area. CoFeB/NF-0.15 catalyst shows excellent HER performance and reaches ?10 mA cm^?2 at overpotential of 35 mV in alkaline solution, and Tafel slope of 84.7 mV dec^?1, indicative of Volmer-Heyrovsky reaction mechanism. The synergistic effect among Fe, Co and B atoms and the more exposed active sites as well as faster electron transfer kinetics collectively contributed to the improved intrinsic activity of CoFeB for HER. Moreover, CoFeB/NF-0.15 exhibits good stability for over 16 h.