Electrospun NiPd Nanoparticles Supported on Polymer Membrane Nanofibers as an Efficient Catalyst for NaBH4 Dehydrogenation

Sodium borohydride (SBH) hydrolysis in the presence of cheap and efficient catalysts has been proposed as a safe and efficient method for generating clean hydrogen energy for use in portable applications. In this work, we synthesized bimetallic NiPd nanoparticles (NPs) supported on poly(vinylidene fluoride-co-hexafluoropropylene) nanofibers (PVDF-HFP NFs) via the electrospinning approach and reported an in-situ reduction procedure of the NPs being prepared by alloying Ni and Pd with varying Pd percentages. The physicochemical characterization provided evidence for the development of a NiPd@PVDF-HFP NFs membrane. The bimetallic hybrid NF membranes exhibited higher H₂ production as compared to Ni@PVDF-HFP and Pd@PVDF-HFP counterparts. This may be due to the synergistic effect of binary components. The bimetallic Ni_1-xPd_x(x = 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3)@PVDF-HFP nanofiber membranes exhibit composition-dependent catalysis, in which Ni₇₅Pd₂₅@PVDF-HFP NF membranes demonstrate the best catalytic activity. The full H₂ generation volumes (118 mL) were obtained at a temperature of 298 K and times 16, 22, 34 and 42 min for 250, 200, 150, and 100 mg dosages of Ni₇₅Pd₂₅@PVDF-HFP, respectively, in the presence of 1 mmol SBH. Hydrolysis utilizing Ni₇₅Pd₂₅@PVDF-HFP was shown to be first order with respect to Ni₇₅Pd₂₅@PVDF-HFP amount and zero order with respect to the [NaBH₄] in a kinetics study. The reaction time of H₂ production was reduced as the reaction temperature increased, with 118 mL of H₂ being produced in 14, 20, 32 and 42 min at 328, 318, 308 and 298 K, respectively. The values of the three thermodynamic parameters, activation energy, enthalpy, and entropy, were determined toward being 31.43 kJ mol^-1, 28.82 kJ mol^-1, and 0.057 kJ mol^-1 K^-1, respectively. It is simple to separate and reuse the synthesized membrane, which facilitates their implementation in H₂ energy systems.

Carbon Coated and Nitrogen Doped Hierarchical NiMo-Based Electrocatalysts with High Activity and Durability for Efficient Borohydride Oxidation

Sodium borohydride is a promising candidate as hydrogen storage material. The direct borohydride fuel cell (DBFC) as an energy conversation device has attracted intensive attention owing to the low theoretical potential of borohydride oxidation reaction (BOR, -1.24 V vs SHE) on the anode. In this paper, the hierarchical sea urchin-like NiMoN@NC coated by thin carbon layer with optimal BH₄^- adsorption characteristic was synthesized as a superior electrocatalyst toward BOR. In 1 M NaOH-0.05 M NaBH₄, the BOR working potentials are only -55 and 44 mV at the current densities of 10 and 200 mA cm^-2 on NiMoN@NC, respectively. Furthermore, the membrane-free DBFC using NiMoN@NC as anodic electrocatalyst shows a maximum power density of 67 mW cm^-2 at room temperature with appreciative stability. This well-designed carbon coated and nitrogen doped transition-metal material with hierarchical nano/microstructure as a highly efficient electrocatalyst shows promising potential and bright prospects in electrocatalysis research and practical application for energy conversion systems of DBFC.

The microstructural refinement and performance improvement of a nanoporous Ag/CeO2 catalyst for NaBH4 oxidation

In this paper, Cu and Ce were added to melt-spun Al-Ag precursor alloys to refine the microstructures of nanoporous Ag and Ag/CeO2 composite catalysts for NaBH4 oxidation. After the precursor alloys were dealloyed in 20% NaOH, calcined in air and corroded again in 50% NaOH, Ag2Al in the precursor alloys was completely removed, and refined nanoporous Ag could be obtained; from this process, the finest microstructures were exhibited by Al84Ag8Cu8. When more than 0.3% Ce was added to the Al84Ag8Cu8 ribbons, a refined nanoporous Ag material that consisted of CeO2 nanorods interspersed between Ag ligaments was obtained. Electrochemical measurements indicated that the catalytic properties were clearly increased due to the Cu addition to the Al-Ag alloy. After Ce was added to the Al84Ag8Cu8 ribbons, the catalytic properties of the resulting material were further improved. In regard to melt-spun Al84Ag8Cu8Ce0.5, the obtained nanoporous Ag/CeO2 presented the best properties, and its current density was 2.5 times that of Al84Ag8Cu8, 3.1 times that of Al90Ag8Cu2 and 2.3 times that of Ag/Ce from the Al79Ag15Ce6 precursor alloy without Cu. It was believed that the core-shell structure composed of Ag and Cu-rich phases formed during dealloying could limit the diffusion of Ag and prevent the coarsening of Ag ligaments. Thus, the refined microstructures could provide a large specific surface or additional active sites for the catalytic reaction. Strong interactions resulted from the many interfaces between the Ag ligaments and interspersed CeO2 nanorods, and the more effective utilization of Ag was due to the decomposition of Ag2Al; this result was the key reason for the clear improvement in catalytic performance.

Recent Advances in the Electro-Oxidation of Urea for Direct Urea Fuel Cell and Urea Electrolysis

This paper provides an overview of recent advances in urea electro-oxidation. Urea sources are abundant from human urine, urea-containing wastewater, and industrial urea, thus becoming an attractive option as anodic fuel for the application in direct urea fuel cells (DUFCs). Besides, as a hydrogen-rich chemical fuel, urea can also be electrolyzed to produce hydrogen for energy storage in the near future. The exact mechanisms of urea decomposition are pretty different in alkaline or neutral mediums and are separately discussed in detail. More importantly, the development of anodic electro-catalysts is of great significance for improving the electrochemical performance of both DUFCs and urea electrolysis cells, which is systematically summarized in our review. Challenges and prospects on the future development of urea electro-oxidation are particularly proposed.