title: Triarylphosphine-stabilized platinum nanoparticles in three-dimensional nanostructured films as active electrocatalysts.
abstract: Ligand-stabilized platinum nanoparticles (Pt NPs) can be used to build well-defined three-dimensional (3-D) nanostructured electrodes for better control of the catalyst architecture in proton exchange membrane fuel cells (PEMFCs). Platinum NPs of 1.7 +/- 0.5 nm diameter stabilized by the water-soluble phosphine ligand, tris(4-phosphonatophenyl)phosphine (TPPTP, P(4-C6H4PO3H2)3), were prepared by ethylene glycol reduction of chloroplatinic acid and subsequent treatment of the isolated nanoparticles with TPPTP. The isolated TPPTP-stabilized Pt NPs were characterized by multinuclear magnetic resonance spectroscopy (31P and 195Pt NMR), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure (EXAFS). The negatively charged TPPTP-Pt NPs were electrostatically deposited onto a glassy carbon electrode (GCE) modified with protonated 4-aminophenyl functional groups (APh). Multilayers were assembled via electrostatic layer-by-layer deposition with cationic poly(allylamine HCl) (PAH). These multilayer films are active for the key hydrogen fuel cell reactions, hydrogen oxidation (anode) and oxygen reduction (cathode). Using a rotating disk electrode configuration, fully mass-transport limited kinetics for hydrogen oxidation was obtained after 3 layers of TPPTP-Pt NPs with a total Pt loading of 4.2 microg/cm2. Complete reduction of oxygen by four electrons was achieved with 4 layers of TPPTP-Pt NPs and a total Pt loading of 5.6 microg/cm2. A maximum current density for oxygen reduction was reached with these films after 5 layers resulting in a mass-specific activity, i(m), of 0.11 A/mg(Pt) at 0.9 V. These films feature a high electrocatalytic activity and can be used to create systematic changes in the catalyst chemistry and architecture to provide insight for building better electrocatalysts.
authors.affiliation: Naval Research Laboratory, 4555 Overlook Avenue, SW, Washington, District of Columbia 20375, USA.
authors.forename: Cynthia N
authors.initials: CN
authors.lastname: Kostelansky
authors.forename: Jeremy J
authors.initials: JJ
authors.lastname: Pietron
authors.forename: Mu-San
authors.initials: MS
authors.lastname: Chen
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Dressick
authors.forename: Karen E
authors.initials: KE
authors.lastname: Swider-Lyons
authors.forename: David E
authors.initials: DE
authors.lastname: Ramaker
authors.forename: Rhonda M
authors.initials: RM
authors.lastname: Stroud
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Klug
authors.forename: Brian S
authors.initials: BS
authors.lastname: Zelakiewicz
authors.forename: Terence L
authors.initials: TL
authors.lastname: Schull