The Fabrication of Mesoporous Palladium-Boron Alloy by a Dual-Force-Driven Self-Assembly Strategy for Enhancing the Electrocatalytic Formic Acid Oxidation Activity

Pd-based catalysts are considered promising for the formic acid oxidation reaction (FAOR), whereas the toxic effect of poisoning intermediates greatly affects the stability and activity of the catalysts. Herein, a dual-force-driven self-assembly strategy is developed to synthesize mesoporous palladium-boron (meso-Pd-B) alloy using cationic polymer polyethyleneimine (PEI) as a pore-forming agent. In this strategy, PEI can interact with the Pd metal precursor via electrostatic and coordination interactions and self-assemble into stable organic-inorganic composites. Dimethylamine borane as a reducing agent together with boric acid enables the alloying of Pd with B, and the Pd-B alloy with mesoporous structure is obtained driven by dual forces. The strategy can be generalized to synthesize other mesoporous metal-B alloys (e.g., Pt-B, Ag-B, Ir-B, Ru-B, and Rh-B). The resultant meso-Pd-B alloy exhibits remarkable catalytic performance (1310 mA mg-1) in FAOR. Combined experimental results and density functional theory calculations indicate that the enhanced activity can be attributed to the electronic effect resulting from the alloying of Pd and B, which weakens the binding strength of toxic substances on the surface of the Pd catalyst. And the favorable mesoporous structure allows the catalyst to expose more catalytic active sites and accelerates the substance transfer efficiency.

Recent Progress on Phase Engineering of Nanomaterials

As a key structural parameter, phase depicts the arrangement of atoms in materials. Normally, a nanomaterial exists in its thermodynamically stable crystal phase. With the development of nanotechnology, nanomaterials with unconventional crystal phases, which rarely exist in their bulk counterparts, or amorphous phase have been prepared using carefully controlled reaction conditions. Together these methods are beginning to enable phase engineering of nanomaterials (PEN), i.e., the synthesis of nanomaterials with unconventional phases and the transformation between different phases, to obtain desired properties and functions. This Review summarizes the research progress in the field of PEN. First, we present representative strategies for the direct synthesis of unconventional phases and modulation of phase transformation in diverse kinds of nanomaterials. We cover the synthesis of nanomaterials ranging from metal nanostructures such as Au, Ag, Cu, Pd, and Ru, and their alloys; metal oxides, borides, and carbides; to transition metal dichalcogenides (TMDs) and 2D layered materials. We review synthesis and growth methods ranging from wet-chemical reduction and seed-mediated epitaxial growth to chemical vapor deposition (CVD), high pressure phase transformation, and electron and ion-beam irradiation. After that, we summarize the significant influence of phase on the various properties of unconventional-phase nanomaterials. We also discuss the potential applications of the developed unconventional-phase nanomaterials in different areas including catalysis, electrochemical energy storage (batteries and supercapacitors), solar cells, optoelectronics, and sensing. Finally, we discuss existing challenges and future research directions in PEN.

Hydrogen in Palladium and Storage Properties of Related Nanomaterials: Size, Shape, Alloying, and Metal-Organic Framework Coating Effects

One of the key issues for an upcoming hydrogen energy-based society is to develop highly efficient hydrogen-storage materials. Among the many hydrogen-storage materials reported, transition-metal hydrides can reversibly absorb and desorb hydrogen, and have thus attracted much interest from fundamental science to applications. In particular, the Pd-H system is a simple and classical metal-hydrogen system, providing a platform suitable for a thorough understanding of ways of controlling the hydrogen-storage properties of materials. By contrast, metal nanoparticles have been recently studied for hydrogen storage because of their unique properties and the degrees of freedom which cannot be observed in bulk, i. e., the size, shape, alloying, and surface coating. In this review, we overview the effects of such degrees of freedom on the hydrogen-storage properties of Pd-related nanomaterials, based on the fundamental science of bulk Pd-H. We shall show that sufficiently understanding the nature of the interaction between hydrogen and host materials enables us to control the hydrogen-storage properties though the electronic-structure control of materials.