In situ grown nanosheet Ni Zn alloy on Ni foam for high performance hydrazine electrooxidation

Durable Pulse-Electrodeposited Ni-Fe-S Nanosheets Supported on a Ni-S Three Dimensional Pattern as Robust Bifunctional Electrocatalysts for Hydrogen Evolution and Urea Oxidation Reactions

This study aims to establish easy-to-fabricate and novel structures for the synthesis of highly active and enduring electrocatalysts for the hydrogen evolution reaction (HER) and urea oxidation reaction (UOR). Gradient electrodeposition and four different time regimes were utilized to synthesize Ni-S 3D patterns with the optimization of electrodeposition time. Pulse electrodeposition was employed for the synthesis of Ni-Fe-S nanosheets at three different frequencies and duty cycles to optimize the pulse electrodeposition parameters. The sample synthesized at 13 min of gradient electrodeposition with a 1 Hz frequency and 0.7 duty cycle for pulse electrodeposition demonstrated the best electrocatalytic performance. The optimized electrode further showed remarkable performance for HER and UOR reactions, requiring only 54 mV and 1.25 V to deliver 10 mA cm-2 for HER and UOR, respectively. Moreover, the overall cell voltage of the two-electrode system in 1 M KOH and 0.5 M urea was measured at 1.313 V, delivering 10 mA cm-2. Constructing Ni-Fe-S nanosheets on 3D Ni-S significantly increased the electrochemical surface area from 51 to 278 for the Ni-S and Ni-Fe-S layers. Tafel slopes were measured as 138 and 182 mV dec-1 for the HER and UOR for the Ni-S coating layer and 97 mV dec-1 for the HER and 131 mV dec-1 for the UOR for the optimal Ni-Fe-S nanosheets on Ni-S. Minimal changes in the potential were observed at 100 mA cm-2 in 50 h regarding the HER and UOR, signifying exceptional electrocatalytic stability. This study provides economically viable, highly active, and long-lasting electrocatalysts suitable for HER and UOR applications.

Porous Ni3Fe intermetallic compounds as efficient and stable catalysts for the hydrogen evolution reaction in alkaline solutions

It is crucial to develop cost-effective novel non-noble metal catalysts with high activity and durability for large-scale industrial hydrogen production via water splitting. Here, based on a facile powder metallurgy method, Ni3Fe intermetallic electrodes with porous structures and controllable phases have been designed and fabricated by sintering mixed Ni and Fe powders under an Ar atmosphere. The effects of sintering temperature on the morphology, porous structure and phase composition of the intermetallic were studied. The resultant Ni3Fe-900 intermetallic electrode exhibits promising HER activity in alkaline electrolytes with an overpotential of 112 mV to drive a current density of 10 mA cm-2. Additionally, the Ni3Fe-900 intermetallic electrode shows good alkali corrosion resistance and stability in the HER process at a current density as high as 500 mA cm-2 for 24 h with no significant changes of the surface morphology, porous structure and phases. The efficient HER performance of the Ni3Fe-900 electrode is attributed to the unique intrinsic activity of the intermetallic electrode, increased accessible active sites originating from the porous structure and accelerated charge transfer. This work provides new insights into the design of electrocatalysts for industrial large-scale hydrogen production by water splitting.

Hierarchical NiZn Solid Solution as a Highly Efficient Palladium Free Heterogeneous Catalyst for Suzuki-Miyaura Cross-Coupling Reaction

In this report, surfactant free solid solution of NiZn with a hierarchical architecture was synthesized via a one-pot colloidal approach. Evidence supporting hierarchical crystal growth and alloying of metals at the atomic level was obtained from field emission scanning electron microscopy and transmission electron microscopy-energy-dispersive X-ray data. Lattice sites of face-centered metallic Ni were found to be occupied by Zn as evident from powder X-ray diffraction where a gradual shift in the peak position and increase in the average lattice parameter upon reduction of the Ni content in the alloy samples can be observed. This well-alloyed, magnetically separable, non-noble metal-based solid solution has the potential to replace the palladium-based catalyst in the Suzuki-Miyaura cross-coupling of aryl halides (-Cl/-Br) and phenylboronic acid. The nanostructured catalyst was formed through the assembly of a triangular spiked and sheet-like structure and is magnetically well separable that is stable enough under the catalytic reaction condition. The developed heterogeneous catalyst and the designed economical catalytic model are the first ever reported work. The catalytic results outperformed most of the reported state-of-the-art works involving the transition metal-based catalyst.

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.

Rational Design of NiZnx@CuO Nanoarray Architectures for Electrocatalytic Oxidation of Methanol

Methanol oxidation reaction (MOR) in anodes is one of the significant aspects of direct methanol fuel cells (DMFCs), which also plays a critical role in achieving a carbon-neutral economy. Designing and developing efficient, cost-effective, and durable non-Pt group metal-based methanol oxidation catalysts are highly desired, but a gap still remains. Herein, we report well-defined hierarchical NiZnx@CuO nanoarray architectures as active electrocatalysts for MOR, synthesized by combining thermal oxidation treatment and magnetron sputtering deposition through a brass mesh precursor. After systematically evaluating the electrocatalytic performance of NiZnx@CuO nanoarray catalysts with different preparation conditions, we found that the NiZn1000@CuO (thermally oxidized at 500 °C for 2 h, nominal thickness of the NiZn alloy film is 1000 nm) electrode delivers a high current density of 449.3 mA cm-2 at 0.8 V for MOR in alkaline media as well as excellent operation stability (92% retention after 12 h). These outstanding MOR performances can be attributed to the hierarchical well-defined structure that can not only render abundant active sites and a synergistic effect to enhance the electrocatalytic activity but also can effectively facilitate mass and electron transport. More importantly, we found that partial Zn atoms could leach from the NiZn alloy, resulting in rough surface nanorods, which would further increase the specific surface area. These results indicate that the NiZn1000@CuO nanoarray architecture could be a promising Pt group metal alternative as an efficient, cost-effective, and durable anode catalyst for DMFCs.

Interface Engineering of Aqueous Zinc/Manganese Dioxide Batteries with High Areal Capacity and Energy Density

Commercialization of aqueous batteries is mainly hampered by their low energy density, owing to the low mass loading of active cathode materials. In this work, a MnO₂ cathode structure (MnO₂ /CTF) is designed to modify the MnO₂ /collector interface for enhanced ion transportation properties. Such a cathode can achieve ultrahigh mass loading of MnO₂ , large areal capacity, and high energy density, with excellent cycling stability and rate performance. Specifically, a 0.15 mm thick MnO₂ /CTF cathode can realize a mass loading of 20 mg cm^-2 with almost 100% electrochemical conversion of MnO₂ , providing the maximum areal capacity of 12.08 mA h cm^-2 and energy density of 191 W h kg^-1 for Zn-MnO₂ /CTF batteries when considering both cathode and anode. Besides the conventional low energy demonstrations, such a Zn-MnO₂ /CTF battery is capable of realistic applications, such as mobile phones in our daily life, which is a promising alternative for wearable electronics.

In Situ Reconstructed Zn doped Fex Ni(1- x ) OOH Catalyst for Efficient and Ultrastable Oxygen Evolution Reaction at High Current Densities

Developing FeOOH as a robust electrocatalyst for high output oxygen evolution reaction (OER) remains challenging due to its low conductivity and dissolvability in alkaline conditions. Herein, it is demonstrated that the robust and high output Zn doped NiOOH-FeOOH (Zn-Fe_x Ni_(1-x) )OOH catalyst can be derived by electro-oxidation-induced reconstruction from the pre-electrocatalyst of Zn modified Ni metal/FeOOH film supported by nickel foam (NF). In situ Raman and ex situ characterizations elucidate that the pre-electrocatalyst undergoes dynamic reconstruction occurring on both the catalyst surface and underneath metal support during the OER process. That involves the Fe dissolution-redeposition and the merge of Zn doped FeOOH with in situ generated NiOOH from NF support and NiZn alloy nanoparticles. Benefiting from the Zn doping and the covalence interaction of FeOOH-NiOOH, the reconstructed electrode shows superior corrosion resistance, and enhanced catalytic activity as well as bonding force at the catalyst-support interface. Together with the feature of superaerophobic surface, the reconstructed electrode only requires an overpotential of 330 mV at a high-current-density of 1000 mA cm^-2 and maintains 97% of its initial activity after 1000 h. This work provides an in-depth understanding of electrocatalyst reconstruction during the OER process, which facilitates the design of high-performance OER catalysts.

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.

A three-dimensional nanostructure of NiFe(OH) X nanoparticles/nickel foam as an efficient electrocatalyst for urea oxidation

Developing high-performance electrocatalysts for urea oxidation reaction (UOR) can not only solve the problem of environmental pollution, but also solve the problem of the energy crisis by producing hydrogen for electrodes. The preparation of porous three-dimensional nanostructures as efficient electrocatalysts has become important work. Here, we developed a novel three-dimensional (3D) nanostructure of NiFe(OH) X nanoparticles/nickel foam with a high active area by a simple electroplating method and a subsequent treatment with ferric ion solution. This structure shows much greater UOR activity than the control sample (Ni/Ni foam) with the potential of 1.395 V (vs. RHE) (with an overpotential of 1.025 V) for driving the current density of 100 mA cm-2 in 1.0 M KOH electrolyte with 0.33 M urea. This work not only provides rapid and large-scale preparation of a three-dimensional nanostructure, but also gives a new way to design and obtain high-performance electrocatalysts.

Recent Developments for the Application of 3D Structured Material Nickel Foam and Graphene Foam in Direct Liquid Fuel Cells and Electrolyzers

Platinum and platinum-based catalysts are some of the most effective catalysts used in fuel cells. However, electrocatalysts used for direct liquid fuel cells (DLFCs) and electrolyzers are high cost and suffer from several other problems, thus hindering their commercialization as power sources to produce clean energy. Common issues in electrocatalysts are low stability and durability, slow kinetics, catalyst poisoning, high catalyst loading, high cost of the catalytic materials, poisoning of the electrocatalysts, and formation of intermediate products during electrochemical reactions. The use of catalyst supports can enhance the catalytic activity and stability of the power sources. Thus, nickel foam and graphene foam with 3D structures have advantages over other catalyst supports. This paper presents the application of nickel foam and graphene foam as catalyst supports that enhance the activities, selectivity, efficiency, specific surface area, and exposure of the active sites of DLFCs. Selected recent studies on the use of foam in electrolyzers are also presented.

A dual-excitation fluorescent probe EuIII-dtpa-bis(HBT) for hydrazine detection in aqueous solutions and living cells

The Eu^III-dtpa-bis(HBT) dual-excitation fluorescence probe has good selectivity and strong anti-interference ability for the detection of N₂H₄.