Simple room temperature synthesis of porous nickel phosphate foams for electrocatalytic ethanol oxidation

Enhanced Isopropyl Alcohol Conversion over Acidic Nickel Phosphate-Supported Zeolite Catalysts

In this preliminary research, the catalytic activity of isopropyl alcohol conversion to diisopropyl ether through dehydration reaction catalyzed by zeolite-Ni and zeolite-Ni(H₂PO₄)₂ was comparatively described. The natural zeolite was treated with 1% HF and 6 N HCl prior to modifications using the impregnation method. Isopropyl alcohol conversion was examined at a mild temperature of 150 °C for 3.5 h on the reflux system with various catalyst loadings. X-ray diffraction and Fourier transform infrared analysis confirmed the successful impregnation of nickel and nickel phosphate into the zeolite. Scanning electron microscopy analysis revealed a cubic-like structure on zeolite-Ni(H₂PO₄)₂, whereas homogenously distributed nickel species were observed on the zeolite-Ni catalyst. Energy-dispersive X-ray spectroscopy analysis reinforced the accomplishment of zeolite modifications. The N₂ physisorption isotherms showed a decline in the surface area and total pore volume of the zeolite because of the blocking of pores. The zeolite-Ni(H₂PO₄)₂ catalyst had higher acidity than unmodified zeolite and zeolite-Ni catalysts, which inherently suggested that the presence of phosphate groups results in higher catalytic activity toward isopropyl alcohol. The highest catalytic activity was attained by 8 mEq/g metal loading zeolite-Ni(H₂PO₄)₂ with isopropyl alcohol conversion of 81.51%, diisopropyl ether yield, and selectivity of 40.77 and 33.16%. The reusability study suggested that the zeolite-Ni(H₂PO₄)₂ catalyst was still active and had sufficient catalytic activity stability toward isopropyl alcohol after the third cycle was reused. This nickel phosphate-based modified zeolite was adequately potential for diisopropyl ether production through isopropyl alcohol dehydration.

Zn Metal Atom Doping on the Surface Plane of One-Dimesional NiMoO4 Nanorods with Improved Redox Chemistry

The effect of zinc (Zn) doping and defect formation on the surface of nickel molybdate (NiMoO₄) structures with varying Zn content has been studied to produce one-dimensional electrodes and catalysts for electrochemical energy storage and ethanol oxidation, respectively. Zn-doped nickel molybdate (Ni_1-xZn_xMoO₄, where x = 0.1, 0.2, 0.4, and 0.6) nanorods were synthesized by a simple wet chemical route. The optimal amount of Zn is found to be around 0.25 above which the NiMoO₄ becomes unstable, resulting in poor electrochemical activity. This result agrees with our density functional theory calculations in which the thermodynamic stability reveals that Ni_1-xZn_xMoO₄ crystallized in the β-NiMoO₄ phase and is found to be stable for x≤0.25. Analytical techniques show direct evidence of the presence of Zn in the NiMoO₄ nanorods, which subtly alter the electrocatalytic activity. Compared with pristine NiMoO₄, Zn-doped NiMoO₄ with the optimized Zn content was tested as an electrode for an asymmetric supercapacitor and demonstrated an enhanced specific capacitance of 122 F g^-1 with a high specific energy density of 43 W h kg^-1 at a high power density of 384 W kg^-1. Our calculations suggest that the good conductivity from Zn doping is attributed to the formation of excess oxygen vacancies and dopants play an important role in enhancing the charge transfer between the surface and OH^- ions from the electrolyte. We report electrochemical testing, material characterization, and computational insights and demonstrate that the appropriate amount of Zn in NiMoO₄ can improve the storage capacity (∼15%) due to oxygen vacancy interactions.

Advanced Catalytic Materials for Ethanol Oxidation in Direct Ethanol Fuel Cells

Direct ethanol fuel cells (DEFCs) have emerged as promising and advanced power systems that can considerably reduce fossil fuel dependence, and thus have attracted worldwide attention. DEFCs have many apparent merits over the analogous devices fed with hydrogen or methanol. As the key constituents, the catalysts for both cathodes and anodes usually face some problems (such as high cost, low conversion efficiency, and inferior durability) that hinder the commercialization of DEFCs. This review mainly focuses on the most recent advances in nanostructured catalysts for anode materials in DEFCS. First, we summarize the effective strategies used to achieve highly active Pt- and Pd-based catalysts for ethanol electro-oxidation, including composition control, microstructure design, and the optimization of support materials. Second, a few non-precious catalysts based on transition metals (such as Fe, Co, and Ni) are introduced. Finally, we outline the concerns and future development of anode catalysts for DEFCs. This review provides a comprehensive understanding of anode catalysts for ethanol oxidation in DEFCs.