Ni- and Co-Based MOF-Derived NixCo3-xO4 Materials: As an Efficient Anode for Direct Methanol Fuel Cell Application

Finding inexpensive and efficient anode materials is crucial for the oxidation of methanol in the direct methanol fuel cell (DMFC), which is the key electrode reaction. Herein, we report metal-organic framework (MOF)-derived Co3O4, NiO, and NixCo3-xO4 (where x = 1.5, 1, and 0.6) materials deposited on nickel foam as efficient anode material for methanol oxidation. Among them, NiCo2O4 exhibited the highest methanol oxidation activity, owing to its lowest charge-transfer resistance (0.097 Ω) and high electrochemically active surface area (1950 cm2), resulting in the lowest onset potential of 0.35 V vs Hg/HgO. The optimized Ni-to-Co ratio and synergistic effect between Ni and Co metals enable NiCo2O4 to achieve the highest mass activity of 151 mA mg-1 and geometric current density of 288 mA cm-2, demonstrating excellent durability over 14 h at 0.6 V. In addition, to optimize methanol concentration, all the electrocatalysts were tested in a range of methanol concentrations, showing 0.5 M methanol as the optimal concentration. This study focuses on optimizing the metal ratio and methanol concentration to achieve the highest catalytic activity. Additionally, this lays the foundation for developing diverse MOF-derived electrocatalysts and advancing DMFCs.

Nickel and cobalt-based tungstate nanocomposites as promising electrocatalysts in alkaline direct methanol fuel cells

In this work, a non-precious group metal (non-PGM) electrocatalyst based on transition metals is introduced as a promising solution for enhancing the efficiency of direct methanol fuel cell (DMFC). Nickel-cobalt mixed tungstate was prepared using a simple co-precipitation method with different molar ratios of Ni, Co and W. The prepared materials were tested and validated using different characterization techniques. It was observed using SEM that the materials are agglomerated amorphous random circular nanocomposite structures. The electrochemical performance of the prepared electrocatalysts revealed that the best nanocomposite was the one with the Ni : Co : W ratio of 1 : 1 : 1.5 (W1.5). This composite showed a higher current density of 229 mA cm-2 towards methanol oxidation at a scan rate of 50 mV s-1 in 1 M methanol at 0.6 V, with the lowest onset potential of 0.33 V. The obtained results present a new strong non-PGM material for direct methanol electro-oxidation reactions and open new doors for economic and earth-abundant electrocatalysts as an alternative to expensive commercially available catalysts.

A three-dimensional flower-like Mn–Ni–Co–O microstructure as a high-performance electrocatalyst for the methanol oxidation reaction

A Mn–Ni–Co–O ternary metal oxide with a unique 3D microstructure shows high electrocatalytic activity and stability towards methanol electrooxidation.

Design of Hierarchical NiCo2O4 Nanocages with Excellent Electrocatalytic Dynamic for Enhanced Methanol Oxidation

Although sheet-like materials have good electrochemical properties, they still suffer from agglomeration problems during the electrocatalytic process. Integrating two-dimensional building blocks into a hollow cage-like structure is considered as an effective way to prevent agglomeration. In this work, the hierarchical NiCo₂O₄ nanocages were successfully synthesized via coordinated etching and precipitation method combined with a post-annealing process. The nanocages are constructed through the interaction of two-dimensional NiCo₂O₄ nanosheets, forming a three-dimensional hollow hierarchical architecture. The three-dimensional supporting cavity effectively prevents the aggregation of NiCo₂O₄ nanosheets and the hollow porous feature provides amounts of channels for mass transport and electron transfer. As an electrocatalytic electrode for methanol, the NiCo₂O₄ nanocages-modified glassy carbon electrode exhibits a lower overpotential of 0.29 V than those of NiO nanocages (0.38 V) and Co₃O₄ nanocages (0.34 V) modified glassy carbon electrodes. The low overpotential is attributed to the prominent electrocatalytic dynamic issued from the three-dimensional hollow porous architecture and two-dimensional hierarchical feature of NiCo₂O₄ building blocks. Furthermore, the hollow porous structure provides sufficient interspace for accommodation of structural strain and volume change, leading to improved cycling stability. The NiCo₂O₄ nanocages-modified glassy carbon electrode still maintains 80% of its original value after 1000 consecutive cycles. The results demonstrate that the NiCo₂O₄ nanocages could have potential applications in the field of direct methanol fuel cells due to the synergy between two-dimensional hierarchical feature and three-dimensional hollow structure.

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.

High activity of NiCo2O4 promoted Pt on three-dimensional graphene-like carbon for glycerol electrooxidation in an alkaline medium

Spinel oxide NiCo₂O₄ supported on a three-dimensional hierarchically porous graphene-like carbon (3D HPG) material has been firstly used to enhance the activity of Pt for glycerol electrooxidation. The addition of NiCo₂O₄ into the Pt/HPG catalyst can significantly improve the catalytic performance for glycerol oxidation. When NiCo₂O₄ is added to the Pt/HPG catalyst, the onset potential is 25 mV more negative than that on the Pt/HPG catalyst without NiCo₂O₄. The current density at -0.3 V on the Pt-NiCo₂O₄ (wt 10 : 1)/HPG electrode is 1.3 times higher than that on the Pt (30 wt%)/HPG electrode. The Pt-NiCo₂O₄ electrode presented in this work shows great potential as an electrocatalyst for glycerol electrooxidation in an alkaline medium.

3D porous nanostructured Ni3N-Co3N as a robust electrode material for glucose fuel cell

Metal nitrides are broadly applicable in the field of electrochemistry due to their excellent electrical properties. In this study, a 3D nanostructured Ni3N-Co3N catalyst was prepared by using a versatile urea glass method, and was tested as an anode catalyst for a glucose fuel cell. The synthesized Ni3N-Co3N exhibits uniform particle dispersion in structure, morphology, and composition, and has a interpenetrating three-dimensional network structure. Notably, the Ni3N-Co3N significantly improved the catalytic activity of glucose oxidation compared to Ni3N, Co3N, and conventional activated carbon electrodes. The superior electrochemical performance could be attributed to its porous structure and unique properties, which provided a fast transport network for charge and mass transfer as well as good synergetic effect. The glucose fuel cell equipped with a Ni3N-Co3N anode achieved 30.89 W m-2 power and 97.66 A m-2 current densities at room temperature. This investigation provides potential directions for the design of cost-effective bimetallic catalysts for a wide range of glucose fuel cell applications.

Significant promotion effects of Ag oxide towards Pd catalysis for ethanol and methanol oxidation reactions

Ag oxides play a crucial role in promoting the catalysis of Pd both for ethanol and methanol oxidation reactions.

New Insights into the Electrocatalytic Mechanism of Methanol Oxidation on Amorphous Ni-B-Co Nanoparticles in Alkaline Media

Despite an increased interest in sustainable energy conversion systems, there have been limited studies investigating the electrocatalytic reaction mechanism of methanol oxidation on Ni-based amorphous materials in alkaline media. A thorough understanding of such mechanisms would aid in the development of amorphous catalytic materials for methanol oxidation reactions. In the present work, amorphous Ni-B and Ni-B-Co nanoparticles were prepared by a simple chemical reduction, and their electrocatalytic properties were investigated by cyclic voltammetry measurements. The diffusion coefficients (D0) for Ni-B, Ni-B-Co0.02, Ni-B-Co0.05, and Ni-B-Co0.1 nanoparticles were calculated to be 1.28 × 10−9, 2.35 × 10−9, 4.48 × 10−9 and 2.67 × 10−9 cm2 s−1, respectively. The reaction order of methanol in the studied transformation was approximately 0.5 for all studied catalysts, whereas the reaction order of the hydroxide ion was nearly 1. The activation energy (Ea) values of the reaction were also calculated for the Ni-B and Ni-B-Co nanoparticle systems. Based on our kinetic studies, a mechanism for the methanol oxidation reaction was proposed which involved formation of an electrocatalytic layer on the surface of amorphous Ni–B and Ni-B-Co nanoparticles. And methanol and hydroxide ions could diffuse freely through this three-dimensional porous conductive layer.

Facile and cost-effective growth of a highly efficient MgCo2O4 electrocatalyst for methanol oxidation

MgCo₂O₄ nanorods show superior electrochemical performance when used as an electrocatalyst for methanol electrooxidation.

Microwave-assisted fast synthesis of hierarchical NiCo2O4 nanoflower-like supported Ni(OH)2 nanoparticles with an enhanced electrocatalytic activity towards methanol oxidation

NiCo₂O₄/Ni(OH)₂ synthesizing through microwave-assisted hydrothermal method and coordination of homogeneous precipitation, exhibiting excellent electrocatalytic activity.

Enhanced tortuosity for electrolytes in microwave irradiated self-organized carbon-doped Ni/Co hydroxide nanocomposite electrodes with higher Ni/Co atomic ratio and rate capability for an asymmetric supercapacitor

We demonstrate a green, facile and rapid microwave-mediated process for fabricating carbon black (CB) incorporated Ni/Co hydroxide porous nanocomposites and study the effect of various mass loading of CB on supercapacitor performance. The structure and interactions between CB and Ni/Co hydroxide are characterized by using x-ray diffraction, Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy, which suggest the miniaturization of the single-phase Ni/Co hydroxide formation time. A morphology study reveals that the addition of CB into Ni/Co hydroxide develops a loose network structure with well-defined architectural pores. In addition, the nanocomposites demonstrate noticeable improvements in porosity and atomic ratio of Ni/Co with an increasing percentage of carbon, which results in a higher diffusion of electrolytes, and hence electrical conduction. The developed electrode materials exhibit a maximum specific capacitance value of 1526 Fg^-1 at current density 1 Ag^-1 with excellent cyclic stability (92% retention at 5000 cycles), energy density (76 Wh Kg^-1), power density (250 W Kg^-1) and rate capability. A solid state asymmetric supercapacitor device is fabricated and utilized to brighten a commercial LED effectively for validating real usage.

Electrochemical growth of Co(OH)2 nanoflakes on Ni foam for methanol electro-oxidation

Co(OH)₂ nanoflakes directly grown on Ni foam using an electrodeposition route exhibit a promising performance for electrocatalytic oxidation of methanol.

Preparation and pseudocapacitive performance of microporous Co3O4–Co nanocomposites on Ni foam substrate

Microporous Co nanoparticles (NPs) with pore diameters of 0.38 nm have been prepared by dealloying Co–Al alloy NPs, which were subsequently annealed at different temperatures to synthesize microporous Co₃O₄–Co nanocomposites as electrode materials for pseudocapacitors.

Tuning the electro-chemical properties by selectively substituting transition metals on carbon in Ni/Co oxide–carbon composite electrodes for supercapacitor devices

Carbon embedded Ni/Co oxide composite electrodes with different carbon percentages were fabricated through SILAR method, which tuned Ni substitution to give improved electro-chemical properties for low-cost supercapacitor devices.

Facile Synthesis of Core/Shell-like NiCo2O4-Decorated MWCNTs and its Excellent Electrocatalytic Activity for Methanol Oxidation

The design and development of an economic and highly active non-precious electrocatalyst for methanol electrooxidation is challenging due to expensiveness of the precursors as well as processes and non-ecofriendliness. In this study, a facile preparation of core-shell-like NiCo₂O₄ decorated MWCNTs based on a dry synthesis technique was proposed. The synthesized NiCo₂O₄/MWCNTs were characterized by infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and selected area energy dispersive spectrum. The bimetal oxide nanoparticles with an average size of 6 ± 2 nm were homogeneously distributed onto the surface of the MWCNTs to form a core-shell-like nanostructure. The NiCo₂O₄/MWCNTs exhibited excellent electrocatalytic activity for the oxidation of methanol in an alkaline solution. The NiCo₂O₄/MWCNTs exhibited remarkably higher current density of 327 mA/cm² and a lower onset potential of 0.128 V in 1.0 M KOH with as high as 5.0 M methanol. The impressive electrocatalytic activity of the NiCo₂O₄/MWCNTs is promising for development of direct methanol fuel cell based on non-Pt catalysts.