Ni 3 S 2 @Ni foam 3D electrode prepared via chemical corrosion by sodium sulfide and using in hydrazine electro-oxidation

Ru-Ni nanoparticles electrodeposited on rGO/Ni foam as a binder-free, stable and high-performance anode catalyst for direct hydrazine fuel cell

Bimetallic Ru-Ni nanoparticles was synthesized on the reduced graphene oxide decorated Ni foam (Ru-Ni/rGO/NF) by electroplating method to be utilized as the anode electrocatalyst for direct hydrazine-hydrogen peroxide fuel cells (DHzHPFCs). The synthesized electrocatalysts were characterized by X-ray diffraction, Field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The electrochemical properties of catalysts towards hydrazine oxidation reaction in an alkaline medium were evaluated by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. In the case of Ru₁-Ni₃/rGO/NF electrocatalyst, Ru₁-Ni₃ provided active sites due to low activation energy (22.24 kJ mol^-1) for hydrazine oxidation reaction and reduced graphene oxide facilitated charge transfer by increasing electroactive surface area (EASA = 677.5 cm²) with the small charge transfer resistance (0.1 Ω cm²). The CV curves showed that hydrazine oxidation on the synthesized electrocatalysts was a first-order reaction in low concentrations of N₂H₄ and the number of exchanged electrons was 3.0. In the single cell of the of direct hydrazine-hydrogen peroxide fuel cell, the maximum power density value of Ru₁-Ni₃/rGO/NF electrocatalyst was 206 mW cm^-2 and the open circuit voltage was 1.73 V at 55 °C. These results proved that the Ru₁-Ni₃/rGO/NF is a promising candidate for using as the free-binder anode electrocatalyst in the future application of direct hydrazine-hydrogen peroxide fuel cells due to its excellent structural stability, ease of synthesis, low cost, and high catalytic performance.

Crystalline-Amorphous Interface Coupling of Ni3S2/NiPx/NF with Enhanced Activity and Stability for Electrocatalytic Oxygen Evolution

The rational design of highly efficient and stable electrocatalysts for the oxygen evolution reaction (OER) is an urgent need but remains challenging for various sustainable energy systems. How to adjust the atomic structure and electronic structure of the active center is a key bottleneck problem. Accelerating the electron transfer process and the deep self-reconstruction of active sites could be a cost-effective strategy toward electrocatalytic OER catalyst development. Here, a crystalline-amorphous (c-a) coupled Ni₃S₂/NiP_x electrocatalyst self-supported on nickel foam with an intimate interface was developed via a feasible solvothermal-electrochemistry method. The coupling interface of the crystalline structure with high conductivity and amorphous structure with numerous potential active sites could regulate the electronic structure and optimize the adsorption/desorption of O-containing species, ultimately resulting in high OER catalytic performance. The obtained Ni₃S₂/NiP_x/NF presents a low OER overpotential of 265 mV to obtain 10 mA·cm^-2 and a small Tafel slope of 51.6 mV·dec^-1. Also, the catalyst with the coupled interface exhibited significantly enhanced long-term stability compared to the other two catalysts, with <5% decay in OER activity over 20 h of continuous operation, while that of Ni₃S₂/NF and NiP_x/NF decreased by about 30 and 50%, respectively. This study provides inspiration for other energy conversion reactions in optimizing the performance of catalysts by coupling crystalline-amorphous structures.

Boosting Electrochemical Water Oxidation on NiFe (oxy) Hydroxides by Constructing Schottky Junction toward Water Electrolysis under Industrial Conditions

The practical deployment of promising NiFe-based oxygen evolution reaction (OER) electrocatalysts is heavily limited due to the constrain in both stability and activity under industrial conditions. Herein, a 3D free-standing NiFe(oxy)hydroxide-based electrode with Schottky junction is constructed, in which NiFe(oxy)hydroxide (NiFe(OH)_x ) nanosheets are chemically assembled on the top of metal-like Ni₃ S₂ scaffold that are in situ formed on commercial Ni mesh. Such an assembly enhances the binding strength of each components, promotes the charge transfer across the interfaces, and modulates the electronic and nanostructural features of NiFe(OH)_x . Consequently, the electrode delivers current densities of as high as 500 and 1000 mA cm^-2 for OER at overpotentials of only 248 and 270 mV with long-term stability in 1 m KOH. When it was paired with a NiMo hydrogen evolution cathode in a practical two-electrode system, a current density of 1000 mA cm^-2 is achieved at a low cell voltage of ≈1.61 V at 80 °C in 30% KOH without losing performance for at least 1500 h. This is the best performance reported thus far for alkaline water electrolysis under industrial conditions, demonstrating its great potential for practical applications.

Co Nanoparticle-Encapsulated Nitrogen-Doped Carbon Nanotubes as an Efficient and Robust Catalyst for Electro-Oxidation of Hydrazine

Structural engineering is an effective methodology for the tailoring of the quantities of active sites in nanostructured materials for fuel cell applications. In the present study, Co nanoparticles were incorporated into the network of 3D nitrogen-doped carbon tubes (Co@NCNTs) that were obtained via the molten-salt synthetic approach at 800 °C. Morphological representation reveals that the Co@NCNTs are encompassed with Co nanoparticles on the surface of the mesoporous walls of the carbon nanotubes, which offers a significant active surface area for electrochemical reactions. The CoNPs/NCNTs-1 (treated with CaCl₂) nanomaterial was used as a potential candidate for the electro-oxidation of hydrazine, which improved the response of hydrazine (~8.5 mA) in 1.0 M NaOH, as compared with CoNPs/NCNTs-2 (treated without CaCl₂), NCNTs, and the unmodified GCE. Furthermore, the integration of Co helps to improve the conductivity and promote the lower onset electro-oxidation potential (−0.58 V) toward the hydrazine electro-oxidation reaction. In particular, the CoNPs/NCNTs-1 catalysts showed significant catalytic activity and stability performances i.e., the i-t curves showed notable stability when compared with their initial current responses, even after 10 days, which indicates the significant durability of the catalyst materials. This work could present a new approach for the design of efficient electrode materials, which can be used as a favorable candidate for the electro-oxidation of liquid fuels in fuel cell applications.

"Carbon quantum dots-glue" enabled high-capacitance and highly stable nickel sulphide nanosheet electrode for supercapacitors

A facile "carbon quantum dots glue" strategy for the fabrication of honeycomb-like carbon quantum dots/nickel sulphide network arrays on Ni foam surface is successfully demonstrated. This design realizes the immobilization of nanosheet arrays and maintains a strong adhesion to the collector, forming a three-dimensional (3D) honeycomb-like architecture. Thanks to the unique structural advantages, the resulting bind-free electrode with high active mass loading of 6.16 mg cm^-2 still exhibits a superior specific capacitance of 1130F g^-1 at 2 A g^-1, and maintains 80% of the initial capacitance even at 10 A g^-1 after 3000 cycles. Furthermore, the assembled asymmetrical supercapacitor delivers an energy density of 18.8 Wh kg^-1 at a power density of 134 W kg^-1, and outstanding cycling stability (100% of initial capacitance retention after 5000 cycles at 5 mA cm^-2). These impressive results indicate a new perspective to design various binder-free electrodes for electrochemical energy storage devices.

Three-dimensional Nanoporous Cu-Doped Ni Coating as Bifunctional Electrocatalyst for Hydrazine Sensing and Hydrogen Evolution Reaction

Developing a cost-effective and efficient bifunctional electrocatalyst with simple synthesis strategy for hydrazine sensing and H evolution reaction (HER) is of utmost importance. Herein, a three-dimensional porous Cu-doped metallic Ni coating on Ti mesh (Ni(Cu) coating/TM) was successfully electrodeposited by a facile electrochemical method. Electrochemical etching of the electrodeposited Ni(Cu) coating with metallic Ni and Cu mixed phase on a Ti mesh contributed to the formation of a three-dimensional porous Cu-doped metallic Ni coating. Owing to the large specific surface area and enhanced electroconductivity caused by the porous structure and Cu doping, respectively, the developed Ni(Cu) coating/TM exhibited superior hydrazine sensing performance and electrocatalytic activity toward hydrogen evolution reaction (HER). The Ni(Cu) coating/TM electrode presented a good sensitivity of 3909μA mM^-1cm^-2and two relatively broad linear ranges from 0.004 mM to 2.915 mM and from 2.915 mM to 5.691 mM as well as a low detection limit of 1.90μM. In addition, the Ni(Cu) coating/TM required a relatively low HER overpotential of 140 mV to reach -10 mA cm^-2and exhibited robust durability in alkaline solution. The excellent hydrazine electrooxidation and HER performance guarantee its promising application in hydrazine detection and energy conversion.

Three dimensional Ni3S2 nanorod arrays as multifunctional electrodes for electrochemical energy storage and conversion applications

The increasing demand for energy and environmental protection has stimulated intensive interest in fundamental research and practical applications. Nickel dichalcogenides (Ni₃S₂, NiS, Ni₃Se₂, NiSe, etc.) are promising materials for high-performance electrochemical energy storage and conversion applications. Herein, 3D Ni₃S₂ nanorod arrays are fabricated on Ni foam by a facile solvothermal route. The optimized Ni₃S₂/Ni foam electrode displays an areal capacity of 1602 µA h cm^-2 at 5 mA cm^-2, excellent rate capability and cycling stability. Besides, 3D Ni₃S₂ nanorod arrays as electrode materials exhibit outstanding performances for the overall water splitting reaction. In particular, the 3D Ni₃S₂ nanorod array electrode is shown to be a high-performance water electrolyzer with a cell voltage of 1.63 V at a current density of 10 mA cm^-2 for overall water splitting. Therefore, the results demonstrate a promising multifunctional 3D electrode material for electrochemical energy storage and conversion applications.

Fabrication of porous NiMn2O4 nanosheet arrays on nickel foam as an advanced sensor material for non-enzymatic glucose detection

In this work, porous NiMn₂O₄ nanosheet arrays on nickel foam (NiMn₂O₄ NSs@NF) was successfully fabricated by a simple hydrothermal step followed by a heat treatment. Porous NiMn₂O₄ NSs@NF is directly used as a sensor electrode for electrochemical detecting glucose. The NiMn₂O₄ nanosheet arrays are uniformly grown and packed on nickel foam to forming sensor electrode. The porous NiMn₂O₄ NSs@NF electrode not only provides the abundant accessible active sites and the effective ion-transport pathways, but also offers the efficient electron transport pathways for the electrochemical catalytic reaction by the high conductive nickel foam. This synergy effect endows porous NiMn₂O₄ NSs@NF with excellent electrochemical behaviors for glucose detection. The electrochemical measurements are used to investigate the performances of glucose detection. Porous NiMn₂O₄ NSs@NF for detecting glucose exhibits the high sensitivity of 12.2 mA mM⁻¹ cm⁻² at the window concentrations of 0.99–67.30 μM (correlation coefficient = 0.9982) and 12.3 mA mM⁻¹ cm⁻² at the window concentrations of 0.115–0.661 mM (correlation coefficient = 0.9908). In addition, porous NiMn₂O₄ NSs@NF also exhibits a fast response of 2 s and a low LOD of 0.24 µM. The combination of porous NiMn₂O₄ nanosheet arrays and nickel foam is a meaningful strategy to fabricate high performance non-enzymatic glucose sensor. These excellent properties reveal its potential application in the clinical detection of glucose.

Sequential partial ion exchange synthesis of composite Ni3S2/Co9S8/NiSe nanoarrays with a lavender-like hierarchical morphology

A hierarchical Ni@Ni₃S₂/Co₉S₈/NiSe composite through sequential partial ion exchange for supercapacitor design.