CuO/Co(OH)2 Nanosheets: A Novel Kind of Electrocatalyst for Highly Efficient Electrochemical Oxidation of Methanol

Metal-Organic Framework-Derived Zinc-Cobalt Oxide Materials as High-Performance Anodes for Direct Methanol Fuel Cell Application

Due to the exhaustion of fossil fuels and rising concerns about environmental pollution, direct methanol fuel cells (DMFCs) have emerged as one of the prominent green energy solutions in recent decades. However, the commercialization of DMFCs faces a significant challenge due to the dependence on expensive noble-metal-based electrode materials and the issue of methanol crossover. Therefore, there has been growing interest in developing cost-effective, high-performance anode catalysts to enhance the methanol oxidation reaction (MOR). In this work, unexplored non-noble transition metal oxide materials, such as metal-organic framework (MOF)-derived ZnO, ZnCo2O4, and Zn2CoO4, were directly synthesized on Ni foam using a simple solvothermal method, followed by calcination. The MOR activity of all the materials was tested in a 0.5 M methanol solution under alkaline conditions. Due to the synergetic effect of combined metallic composition, mixed metal oxides exhibited superior performance. The order of MOR activity was measured to be ZnO < Zn2CoO4 < ZnCo2O4. Particularly, ZnCo2O4 exhibited the highest mass activity (42.64 mA mg-1) and geometric current density (166.28 mA cm-2), outperforming Zn2CoO4 (27.44 mA mg-1) and ZnO (12.72 mA mg-1). It also demonstrated the lowest onset potential of 1.32 V (vs RHE) compared to Zn2CoO4 (1.35 V) and ZnO (1.39 V) and maintained excellent long-term stability for 12 h at 1.5 V (vs RHE). Additionally, to determine the optimal methanol concentration, all electrocatalysts were tested across a range of methanol concentrations from 0.1 to 1 M, showing 0.5 M methanol as the most suitable concentration. This study aims to develop cost-effective MOF-derived electrode materials and optimize methanol concentration to maximize catalytic activity. Furthermore, it establishes a foundation for the development of various MOF-derived electrocatalysts and the advancement of DMFC technology.

Enhanced methanol electro-oxidation activity of CuO nanoparticles derived from the thermal decomposition of a CuII salophen type coordination compound

Electrocatalysts based on Cu compounds have been considered as a suitable alternative to platinum compounds due to their low cost, high abundance, excellent redox properties, and performing the methanol oxidation reaction (MOR) at low potentials. This article represents a study of CuO nanoparticles (NPs) prepared through a simple method of thermal decomposition of the CuL coordination compound (H2L = N,N'-bis(salicylidene)-4-chloro-1,2-diaminobenzene), C20H13ClCuN2O2, as a precursor by different electrochemical methods. A comparison of the MOR ability of precursor (CuL) and CuO NPs shows that both compounds are active, but CuO NPs present a peak current density of about 248 mA cm- 2 when screened for catalytic MOR in 1.0 M KOH with 0.5 M methanol, which is superior to the performance of CuL and some previously reported related catalysts based on CuO. The methanol oxidation peak at 0.69 V vs. Ag/AgCl is also more intense than CuL (0.77 V). The modified electrode with CuO NPs also shows lower onset potential, lower Tafel slope, higher electrochemically active surface area (ECSA) and better stability compared to the CuL electrode. These advantages can be assigned to the higher activity of catalytic sites and the lower charge transfer resistance of CuO due to its higher electrical conductivity than the CuL.

Efficiently Re-Utilizing the High-Value Metals in the Spent LiNi1-x-yMnxCoyO2 for the Trifunctional Electrocatalysts by a Novel One-Pot Method

Traditional hydrometallurgy methods for recycling the spent lithium-ion battery materials face some challenges, including the complex processes, and difficulties in separating Ni/Co/Mn. To address these issues, this work proposes a simple one-pot method to achieve a high Li leaching efficiency (99.2%) and simultaneously transform the majority of Ni (99.5%) and Co (99.9%) into a high-performance multifunctional electrocatalyst (LNMCO-HS-180). LNMCO-HS-180 with single-phase structure shows a hollow microsphere morphology. LNMCO-HS-180 can efficiently catalyze the oxygen reduction (ORR), oxygen evolution (OER), and methanol oxidation reactions (MOR), with the ORR half-wave potential of 0.732 V and, OER potential of 1.469 V at 10 mA cm-2. This is mainly attributed to the unique hollow microsphere morphology, suitable Ni/Co/Mn oxidation states, and reduction in the free energy barriers for OER and ORR. Additionally, LNMCO-HS-180 exhibits an MOR potential of only 1.43 V at 100 mA cm-2 and excellent formate selectivity (>99%).

Recycling the Spent LiNi1- x - yMnxCoyO2 Cathodes for High-Performance Electrocatalysts toward Both the Oxygen Catalytic and Methanol Oxidation Reactions

The traditional recycling methods of the spent lithium ion batteries (LIBs) involve the intricate and cumbersome steps. This work proposes a facile method of acid leaching followed by the sulfurization treatment to achieve the high Li leaching efficiency, and obtain high-performance multi-function electrocatalysts for oxygen reduction (ORR), oxygen evolution (OER), and methanol oxidation reactions (MOR) from the spent LIB ternary cathodes. By this method, the Li leaching efficiency from the spent LIB ternary cathode can reach 98.3%, and the transition metal sulfide heterostructures (LNMCO-H-450S) consisting MnS, NiS2, and NiCo2S4 phases can be obtained. LNMCO-H-450S shows the superior bifunctional oxygen catalytic activities with ORR half-wave potential of 0.763 V and OER potential at 10 mA cm-2 of 1.561 V, surpassing most of the state-of-the-art electrocatalysts. LNMCO-H-450S also demonstrates the superior MOR catalytic activity with the potential at 100 mA cm-2 being 1.37 V. Using LNMCO-H-450S as the oxygen catalyst, this work can construct the aqueous and solid-state zinc-air batteries with high power density of 309 and 257 mW cm-2, respectively. This work provides a promising strategy for the efficient recovery of Li, and reutilization of Ni, Co, and Mn from the spent LIB ternary cathodes.

Enhanced Hydroxyl Adsorption in Ultrathin NiO/Cr2 O3 In-Plane Heterostructures for Efficient Alkaline Methanol Oxidation Reaction

The exploration of advanced nickel-based electrocatalysts for alkaline methanol oxidation reaction (MOR) holds immense promise for value-added organic products coupled with hydrogen production, but still remain challenging. Herein, we construct ultrathin NiO/Cr2 O3 in-plane heterostructures to promote the alkaline MOR process. Experimental and theoretical studies reveal that NiO/Cr2 O3 in-plane heterostructures enable a favorable upshift of the d-band center and enhanced adsorption of hydroxyl species, leading to accelerated generation of active NiO(OH)ads species. Furthermore, ultrathin in-plane heterostructures endow the catalyst with good charge transfer ability and adsorption behavior of methanol molecules onto catalytic sites, contributing to the improvement of alkaline MOR kinetics. As a result, ultrathin NiO/Cr2 O3 in-plane heterostructures exhibit a remarkable MOR activity with a high current density of 221 mA cm-2 at 0.6 V vs Ag/AgCl, which is 7.1-fold larger than that of pure NiO nanosheets and comparable with other highly active catalysts reported so far. This work provides an effectual strategy to optimize the activity of nickel-based catalysts and highlights the dominate efficacy of ultrathin in-plane heterostructures in alkaline MOR.

Tailoring the Activity of Electrocatalytic Methanol Oxidation on Cobalt Hydroxide by the Incorporation of Catalytically Inactive Zinc Ions

Catalytically inactive Zn2+ is incorporated into cobalt hydroxide to synthesize hierarchical ZnCo-layered double hydroxide nanosheet networks supported on carbon fiber (ZnCo-LDH/CF). The incorporation of Zn2+ is revealed to endow ZnCo-LDH/CF with significantly superior performance in the aspects of the activity and selectivity for methanol electrooxidation to formic acid and the boosting effect for cathodic hydrogen production compared with the counterpart without Zn2+. Density functional theory (DFT) calculation reveals that the incorporation of nonactive Zn2+ can increase the density of states near the Fermi level of LDH (i.e., elevate electrical conductivity to form favorable charge transportation during electrocatalysis) and promote the adsorption and subsequent cleavage of methanol, thus leading to the enhanced methanol electrooxidation performance.

Enhancement of photoelectrocatalytic performance of copper cobaltate nanoflowers modified with 5,10,15,20-tetrakis(4-carboxylphenyl)porphyrin for methanol oxidation under light

With the continuously increasing global energy demand, there is an urgent requirement to find efficient methanol oxidation reaction (MOR) catalysts that can replace precious metals. In this work, we have elaborately integrated 5,10,15,20-tetrakis(4-carboxyphenyl) porphyrin (H₂TCPP) with copper cobaltate (CuCo₂O₄), which possesses efficient separation of photogenerated charges and increased active sites. The mass activity of H₂TCPP/CuCo₂O₄ (534.75 mA mg^-1) toward MOR is higher than that of pure CuCo₂O₄ (291.75 mA mg^-1) under light. In addition, H₂TCPP/CuCo₂O₄ can catalyze the oxidation of other alcohols, such as ethanol, ethanediol, isopropanol, and glycerol. This study demonstrates that it is feasible to enhance the MOR activity by the modification of bimetallic transition metal oxides with porphyrins.

Activating RuOCo Interaction on the a-Co(OH)2 @Ru Interface for Accelerating the Volmer Step of Alkaline Hydrogen Evolution

The state-of-the-art active hydrogen evolution reaction (HER) catalysts in acid electrolytes generally lose considerable catalytic performance in alkaline electrolytes mainly due to the additional water dissociation step. Designing composite materials is an effective strategy to accelerate alkaline water electrolysis by optimizing the electronic structure of materials. Here, different phases of Co(OH)₂ -supported Ru clusters (α/β-Co(OH)₂ @Ru) are prepared for enabling a highly efficient electrocatalytic HER performance in alkaline solution. The prepared α-Co(OH)₂ nanosheets facilitate the loading of uniform and high-density Ru clusters and the formed highly active RuOCo bonds at the interface. The synergistic interaction endows the hybrid catalyst with low overpotential of 33 mV at 10 mA cm^-2 . Moreover, the homemade anion exchange membrane water electrolysis cell based on α-Co(OH)₂ @Ru affords a cell voltage of 2 V to drive a current density of 270 mA cm^-2 and performs stably during continuous operation for over 100 h. Density functional theory calculations demonstrate that active RuOCo bonds in α-Co(OH)₂ @Ru optimize the energy barriers for H₂ O dissociation and OH^- desorption to facilitate the Volmer reaction step. This work offers a strategy for designing interfacial chemical bonds for high electrocatalytic activity.

Crystalline-Amorphous Ni3S2-NiMoO4 Heterostructure for Durable Urea Electrolysis-Assisted Hydrogen Production at High Current Density

Developing bifunctional catalysts with good performance at a high current density for the urea oxidation reaction (UOR) and the hydrogen evolution reaction (HER) can effectively relieve the severe environmental and energy pressures. Herein, amorphous NiMoO₄ decorated Ni₃S₂ grown on nickel foam (Ni₃S₂-NiMoO₄/NF) is prepared to accelerate UOR and HER. The crystalline-amorphous heterostructure could regulate the interfacial electron structure to reduce the electron density near Ni₃S₂ for optimizing UOR and HER. The decoration of NiMoO₄ enhances its anti-poisoning ability for CO-intermediate species to show good stability at high current densities. Meanwhile, the nano-/microstructure with high hydrophilicity improves mass transfer and the accessibility of electrolyte. Driving high current densities of ±1000 mA cm^-2, it merely needs 1.38 V (UOR) and -263 mV (HER). For urea electrolysis, it can deliver 1000 mA cm^-2 at 1.73 V and stably operate at 500 mA cm^-2 for 120 h. Therefore, this study provides new ideas for durable urea electrolysis-assisted H₂ production.

Cobalt Single Atoms Enabling Efficient Methanol Oxidation Reaction on Platinum Anchored on Nitrogen-Doped Carbon

Developing efficient platinum (Pt)-based electrocatalysts with high tolerance to CO poisoning for the methanol oxidation reaction is critical for the development of direct methanol fuel cells. In this work, cobalt single atoms are introduced to enhance the electrocatalytic performance of N-doped carbon supported Pt (N-C/Pt) for the methanol oxidation reaction. The cobalt single atoms are believed to play a critical role in accelerating the prompt oxidation of CO to CO₂ and minimizing the CO blocking of the adjacent Pt active sites. Benefitting from the synergistic effects among the Co single atoms, the Pt nanoparticles, and the N-doped carbon support, the Co-modified N-C/Pt (Co-N-C/Pt) electrocatalyst simultaneously delivers impressive electrocatalytic activity and durability with lower onset potential and superb CO poisoning resistance as compared to the N-C/Pt and the commercial Pt/C electrocatalysts.

Electrocatalytic Glycerol Oxidation with Concurrent Hydrogen Evolution Utilizing an Efficient MoOx /Pt Catalyst

Glycerol electrolysis affords a green and energetically favorable route for the production of value-added chemicals at the anode and H₂ production in parallel at the cathode. Here, a facile method for trapping Pt nanoparticles at oxygen vacancies of molybdenum oxide (MoO_x ) nanosheets, yielding a high-performance MoO_x /Pt composite electrocatalyst for both the glycerol oxidation reaction (GOR) and the hydrogen evolution reaction (HER) in alkaline electrolytes, is reported. Combined electrochemical experiments and theoretical calculations reveal the important role of MoO_x nanosheets for the adsorption of glycerol molecules in GOR and the dissociation of water molecules in HER, as well as the strong electronic interaction with Pt. The MoO_x /Pt composite thus significantly enhances the specific mass activity of Pt and the kinetics for both reactions. With MoO_x /Pt electrodes serving as both cathode and anode, two-electrode glycerol electrolysis is achieved at a cell voltage of 0.70 V to reach a current density of 10 mA cm^-2 , which is 0.90 V less than that required for water electrolysis.

Porous Tungsten Oxide: Recent Advances in Design, Synthesis, and Applications

Tungsten oxide (WO₃ ) has received ever more attention and has been highly researched over the last decade due to its being a low-cost transition metal semiconductor with tunable, yet widely stable, band gaps. This minireview briefly highlights the challenges in the design and synthesis of porous WO₃ including methods, precursors, solvent effects, crystal phases, and surface activities of the porous WO₃ base material. These topics are explored while also drawing a connection of how the morphology and crystal phase affect the band gap. The shifts in band gap not only impact the optical properties of tungsten but also allow tuning to operate on different energy levels, which makes WO₃ highly desirable in many applications such as supercapacitors, batteries, solar cells, catalysts, sensors, smart windows, and bioapplications.

Intrinsic Oxidase-like Nanoenzyme Co4S3/Co(OH)2 Hybrid Nanotubes with Broad-Spectrum Antibacterial Activity

Improving the antibacterial activity of nanomaterials and avoiding the use of H₂O₂ are vital for biosecurity and public health. In this work, novel Co₄S₃/Co(OH)₂ hybrid nanotubes (HNTs) for the first time were successfully synthesized through the control of Na₂S treatment of Co(CO₃)_0.35Cl_0.20(OH)_1.10 precursor. On the basis of Kirkendall effect, acicular precursor was vulcanized to form Co₄S₃/Co(OH)₂ HNTs that possess great properties including favorable storage ability and ideal stability. By tailoring the composition and structure, Co₄S₃/Co(OH)₂ HNTs were found to have profound oxidase-like catalytic activities. When pH = 3 precursor was treated with 900 mg of Na₂S, Co₄S₃/Co(OH)₂ HNTs exhibit superior performance. Owing to the outstanding oxidase-like activity, Co₄S₃/Co(OH)₂ HNTs can eliminate Escherichia coli, Pseudomonas aeruginosa, Staphylococcus sciuri, and Bacillus without the help of H₂O₂. It turned out that the sterilization ability came from the superoxide anion radical generated by Co₄S₃/Co(OH)₂ HNTs. With Co₄S₃/Co(OH)₂ HNTs, the intracellular reactive oxygen species level can be enhanced and the toxicity of H₂O₂ can be absolutely avoided. Overall, the synthesis of antibacterial nanomaterials is unparalleled and the results of this work would facilitate the utilization in medical science, new energy, and environmental catalysis.

The preparation of NiO/Ni–N/C nanocomposites and its electrocatalytic performance for methanol oxidation reaction

The NiO/Ni–N/C nanocomposites were prepared through hydrothermal method and further carbonization. The NiO/Ni–N/C₅₀₀ displays the highest MA (1043 mA mg_Ni⁻¹) and SA (18.57 mA cm⁻²) for methanol oxidation reaction.

Strained lattice platinum–palladium alloy nanowires for efficient electrocatalysis

The ability to manipulate Pt-based alloy catalysts with controllable compositions and the type of surface facet is important for advancing direct alcohol fuel cells (DAFEs).

Self-template synthesis of defect-rich NiO nanotubes as efficient electrocatalysts for methanol oxidation reaction

Developing robust and inexpensive non-noble metal based anode electrocatalysts is highly desirable for alkaline direct methanol fuel cells (ADMFCs). Herein, we successfully develop a facile self-template synthetic strategy for gram-grade porous NiO nanotubes (NTs) by pyrolyzing a nanorod-like Ni-dimethylglyoxime complex. The pyrolysis temperature highly correlates with the morphology and crystallinity of NiO NTs. The optimal NiO NTs exhibit a large electrochemically active surface area, a fast catalytic kinetics, and a small charge transfer resistance, which induce an outstanding electrocatalytic activity for the methanol oxidation reaction (MOR). Compared with conventional NiO nanoparticles, NiO NTs achieve a 11.5-fold increase in mass activity at 1.5 V for the MOR due to nanotubal morphology and abundant non-vacancy defects on the NiO NT surface. Moreover, NiO NTs have a higher electrocatalytic activity for the intermediates of the MOR (such as formaldehyde and formate) than conventional NiO nanoparticles, which also contribute to MOR activity enhancement. Given the facile synthesis and enhanced electrocatalytic performance, NiO NTs may be promising anode electrocatalysts for ADMFCs.