Facile Synthesis of Three‐Dimensional Pt‐TiO₂ Nano‐networks: A Highly Active Catalyst for the Hydrolytic Dehydrogenation of Ammonia–Borane

Abstract

Three-dimensional (3D) porous metal and metal oxide nanostructures have received considerable interest because organization of inorganic materials into 3D nanomaterials holds extraordinary properties such as lowd ensity, high porosity,a nd high surface area. Supramolecular selfassembled peptide nanostructures were exploited as an organic template for catalytic 3D Pt-TiO 2 nano-network fabrication. A 3D peptide nanofiber aerogel was conformally coated with TiO 2 by atomic layer deposition (ALD) with angstrom-level thickness precision. The 3D peptide-TiO 2 nano-network was further decorated with highly monodisperse Pt nanoparticles by using ozone-assisted ALD.T he 3D TiO 2 nano-network decorated with Pt nanoparticles shows superior catalytic activity in hydrolysis of ammonia-borane,g enerating three equivalents of H 2 .The three-dimensional (3D) porous metal and metal oxide aerogels have recently attracted enormous interest, because assembly of bulk inorganic materials into 3D nanomaterials generates exciting features such as low density,high porosity, and high surface area.[1] Porous 3D aerogels allow rapid flow of electrons,i ons,a nd molecules,w hich makes them extremely attractive for applications such as catalysis, [2] sensing, [3] fuel cells, [4] and supercapacitors.[5] Numerous techniques have been developed to prepare porous metal and metal oxide nanomaterials,including templating,combustion, cathodic corrosion, and aerogel formation.[4b] However, as ignificant challenge exists to synthesize metal and metal oxide 3D nanomaterials in controlled and reproducible manner.T herefore,uniform and highly controlled deposition of metals and metal oxides at ambient temperatures on soft organic templates,which can assemble into desired structures (1D,2D, and 3D), shape and morphology,could be apromising strategy to prepare variety of porous inorganic 3D nanomaterials.S elf-assembling peptides are ac lass of supramolecular polymers,w hich exploit noncovalent interactions such as hydrogen bonding,h ydrophobic, electrostatic, p-p, and van der Waals interactions to generate well-defined supramolecular nanostructures including nanospheres,n anosheets,n anotubes,a nd nanofibers.[6] These versatile supramolecular polymers can encapsulate large amounts of water to form gels,w hich have been extensively utilized as 2D and 3D scaffolds.[7] Critical and air-dried self-assembled peptide nanofiber gels can form self-standing porous 3D aerogels and xerogels,w hich are made up of highly dense 1D nanofibers. These 3D aerogels can be used as soft templates to deposit and support various inorganic nanomaterials from 1D to 3D. [8] Atomic layer deposition (ALD) is ac hemical vapor deposition technique based on sequential, self-limiting surface reactions between gaseous precursors and asolid surface to deposit materials in an atomic layer-by-layer fashion, which paves the way for controlling the film thickness and size of nanoparticles by the number of growth cycles.[9] It provides unmatched capabilities for highly uniform c...

Carboxylic acid Functionalized Cage‐Type Mesoporous Silica FDU‐12 as Support for Controlled Synthesis of Platinum Nanoparticles and Their Catalytic Applications

“…The turnover frequency( TOF) reached 139.3 mol H 2 min À1 mol À1 cat on using the most active catalyst, Pt@CF-12, which is comparable to those of other Pt-based catalysts on silica supports. [44,53,[55][56][57][58][59][60][61][62] Ta ble 2l ists the TOFs of previously reported Pt-based catalysts on different supports for the hydrolysis of ammonia borane.…”

“…However,t he catalytic activity of Pt NPs embedded in silica nanospheres( Pt@SiO 2 core-shell) was slightly higher than that of Pt@CF-12 due to the exceptional core-shells tructure of the catalyst. [55] The core could act as an anoreactor with high concentration of AB molecules and thus enhance the catalytic efficiency.T he higher activities of Pt NPs on supports other than SiO 2 ,s uch as CNTs, [59] TiO 2 , [60] MIL, [44] and g-Al 2 O 3 , [61] can be relatedt ot heir unique textural properties, distinct surface chemistry,a nd interaction between the Pt NPs andt he oxides. The volumeo fH 2 generatedw ith different dosages of the Pt@CF-12 catalysta nd amounts of AB werem easured to explore the reactionk inetics.…”

Polymer decoration of carbon support to boost Pt-catalyzed hydrogen generation activity and durability

“…The probe reaction chosen in the present study is catalytic hydrolytic dehydrogenation of ammonia borane (NH3BH3, AB) over Pt catalyst supported on the noncovalently-functionalized carbon support developed below. This process, known as a structure-sensitive reaction, has been widely employed as a model reaction to understand the catalyst structure-performance relations [16][17][18][19][20], and as a promising route to produce hydrogen at mild conditions for fuel cell applications [21][22][23][24]. Such structure sensitivity originates from the chemistry mainly happened on the Pt(111) active sites [25], and the ability to adsorb and activate reactants [26] as well as promote the rate determining step of NH3BH2*+H2O*→NH3BH2OH*+H* [27,28].…”

Interface Engineering of Colloidal CdSe Quantum Dot Thin Films as Acid-Stable Photocathodes for Solar-Driven Hydrogen Evolution

“…Bifunctional cobalt oxide (CoO x ) films deposited by ALD have been reported to enhance the PEC activity of photoanodes in alkaline solution; , however, only few ALD materials possess the necessary bifunctionality for photocathode applications. ALD platinum nanoparticles and ultrathin conformal films have been well-studied as catalysts for various heterogeneous reactions, such as oxygen reduction, , CO oxidation, dehydrogenation, and tandem hydrogenation; yet, they have rarely been used as a simultaneous passivating layer and cocatalyst on photocathodes for the HER. , Moreover, Pt films deposited by ALD are highly stable and efficient in an acidic electrolyte, indicating the potential of enabling Pt-passivated colloidal semiconductor NCs to serve as efficient and acid-stable photocathodes.…”