Synthesis and electrochemical study of nanoporous Pd–Ag alloys for hydrogen sorption

Mechanical Exfoliation of Expanded Graphite to Graphene-Based Materials and Modification with Palladium Nanoparticles for Hydrogen Storage

Hydrogen is a promising green fuel carrier that can replace fossil fuels; however, its storage is still a challenge. Carbon-based materials with metal catalysts have recently been the focus of research for solid-state hydrogen storage due to their efficacy and low cost. Here, we report on the exfoliation of expanded graphite (EG) through high shear mixing and probe tip sonication methods to form graphene-based nanomaterial ShEG and sEG, respectively. The exfoliation processes were optimized based on electrochemical capacitance measurements. The exfoliated EG was further functionalized with palladium nanoparticles (Pd-NP) for solid-state hydrogen storage. The prepared graphene-based nanomaterials (ShEG and sEG) and the nanocomposites (Pd-ShEG and Pd-sEG) were characterized with various traditional techniques (e.g., SEM, TEM, EDX, XPS, Raman, XRD) and the advanced high-resolution pair distribution function (HRPDF) analysis. Electrochemical hydrogen uptake and release (QH) were measured, showing that the sEG decorated with Pd-NP (Pd-sEG, 31.05 mC cm-2) and ShEG with Pd-NP (Pd-ShEG, 24.54 mC cm-2) had a notable improvement over Pd-NP (9.87 mC cm-2) and the composite of Pd-EG (14.7 mC cm-2). QH showed a strong linear relationship with an effective surface area to volume ratio, indicating nanoparticle size as a determining factor for hydrogen uptake and release. This work is a promising step toward the design of the high-performance solid-state hydrogen storage devices through mechanical exfoliation of the substrate EG to control nanoparticle size and dispersion.

Remarkably improved electrochemical hydrogen storage by multi-walled carbon nanotubes decorated with nanoporous bimetallic Fe-Ag/TiO2 nanoparticles

Nanoporous bimetallic Fe-Ag nanoparticles (NPs) were synthesized using a facile chemical reduction method and used to decorate the surface of multi-walled carbon nanotubes (MWCNTs) for hydrogen sorption and storage. The effect of TiO2 nanoparticles on the hydrogen storage properties of Fe-Ag/CNTs was further studied in detail. For this purpose, several nanocomposites of nanoporous bimetallic Fe-Ag/TiO2 nanoparticles with different amounts of bimetallic Fe-Ag NPs were prepared via a hydrothermal method. The hydrogen storage capacity of the as-prepared nanocomposites was studied using electrochemical methods. The Fe-Ag/TiO2/CNT nanocomposite with 0.04 M bimetallic Fe-Ag NPs showed the highest capacity for hydrogen storage, which was ∼5× higher than that of pristine MWCNTs. The maximum discharge capacity was 2931 mA h g-1, corresponding to a 10.94 wt% hydrogen storage capacity. Furthermore, a 379% increase in discharge capacity was measured after 20 cycles. These results show that Fe-Ag/TiO2/CNT electrodes display superior cycling stability and high reversible capacity, which is attractive for battery applications.

Core-shell Au@Pd nanoparticles with enhanced catalytic activity for oxygen reduction reaction via core-shell Au@Ag/Pd constructions

Core-shell nanoparticles often exhibit improved catalytic properties due to the lattice strain created in these core-shell particles. Herein, we demonstrate the synthesis of core-shell Au@Pd nanoparticles from their core-shell Au@Ag/Pd parents. This strategy begins with the preparation of core-shell Au@Ag nanoparticles in an organic solvent. Then, the pure Ag shells are converted into the shells made of Ag/Pd alloy by galvanic replacement reaction between the Ag shells and Pd²⁺ precursors. Subsequently, the Ag component is removed from the alloy shell using saturated NaCl solution to form core-shell Au@Pd nanoparticles with an Au core and a Pd shell. In comparison with the core-shell Au@Pd nanoparticles upon directly depositing Pd shell on the Au seeds and commercial Pd/C catalysts, the core-shell Au@Pd nanoparticles via their core-shell Au@Ag/Pd templates display superior activity and durability in catalyzing oxygen reduction reaction, mainly due to the larger lattice tensile effect in Pd shell induced by the Au core and Ag removal.

Carbon-supported hollow palladium nanoparticles with enhanced electrocatalytic performance

A facile route was demonstrated for the synthesis of carbon-supported hollow structured Pd nanoparticles with enhanced electrocatalytic properties.

Electrocatalysis and photoelectrochemistry based on functional nanomaterials

Catalysis plays a key role in chemical production, energy processing, air purification, water treatment, food processing, and the life sciences. Nanostructured materials with high surface areas and some unique properties have received widespread interest in electrocatalysis and photocatalysis. Recently, the author’s research team has designed and studied a variety of novel functional nanomaterials. This review article is derived from the author’s 2013 Canadian Catalysis Lectureship Award Lecture and focuses primarily on the electrocatalytic activities of platinum- and palladium-based nanomaterials and the development of TiO2-based nanostructured photocatalysts. Palladium possesses several exceptional properties that may enable promising applications in hydrogen detection, purification, and storage. The significant roles of palladium-based nanomaterials in facilitating the growth of a hydrogen economy are addressed. As platinum-based catalysts are vital to the development of fuel cells and sensors, the design of high-performance platinum-based electrocatalysts is highlighted. Additionally, TiO2 is considered to be one of the most promising photocatalysts due to its nontoxicity, high stability, and cost effectiveness. The modification of TiO2 nanomaterials to achieve visible light response is discussed as well. It is anticipated that the development of advanced functional nanostructured catalysts will further improve the efficiency and reduce the cost of electrochemical and photochemical processes, making them more attractive in addressing the pressing global energy and environmental issues.