Joshua P. McClure

Non-precious Mn1.5Co1.5O4–FeNx/C nanocomposite as a synergistic catalyst for oxygen reduction in alkaline media

In this study we show a method of preparing a high performing catalyst by designing functional nano boundaries in a nanocomposite material. A non-precious nanocomposite material composed of spinel Mn1.5Co1.5O4 nano crystals and FeNx-functioned graphene nano platelets (FeNx/C) was synthesized by an ultrasonic process. The crystal structure and elemental composition of the bimetal oxide were determined by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). The surface morphology of the Mn1.5Co1.5O4–FeNx/C nanocomposite was characterized with transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The catalytic activity for the oxygen reduction reaction (ORR) was analyzed by an electrochemical method. The enhancement of activity for the ORR at the nanocomposite material is attributed to double synergistic effects from the bimetal particles and the FeNx/C nano sheets. The nanocomposite material is able to catalyze 4-electron oxygen reduction to generate water in alkaline media with a high kinetic rate constant (7.6 × 10−2 cm s−1 at 0.7 V vs. reversible hydrogen electrode, RHE). Finally, the activity and stability of the nanocomposite material were compared with that of 40% Pt supported on active carbon (40% Pt/C), which reaches 95% activity and a comparable stability of 40% Pt/C at 0.7 V (vs. RHE).

Directed assembly of bimetallic nanoarchitectures by interfacial photocatalysis with plasmonic hot electrons

Targeted, sequential deposition of metals using localized surface plasmon resonance (LSPR) is a promising fabrication route for solar fuel catalysts and sensors. This work examines liquid-phase, reductive photodeposition of platinum (Pt) nanoparticles onto the longitudinal ends of gold nanorods (AuNR) under surface plasmon excitation. Reductive Pt nucleation is initiated by plasmonic hot electrons at the Au-liquid interface, whose sites are governed by the plasmon polarity. In this work, in situ spectroscopic monitoring of the photodeposition process permitted real-time feedback into AuNR surface functionalization with the Pt precursor, Pt growth kinetics under monochromatic AuNR LSPR excitation, and their evolving light-matter interactions. Energy dispersive spectroscopy (EDS) mappings show Pt deposition was localized toward the AuNR ends. Coordinated X-ray photoelectron spectroscopy (XPS) measurements with density functional theory (DFT) calculations of the Pt-decorated AuNR density of states (DOS) elucidated optoelectronic behavior. Catalytic photodeposition using plasmonic hot electrons provide an economical path towards targeted, hierarchal assembly of multi-metallic nanoarchitectures at ambient conditions with specified optoelectronic activity.

A Rapid Synthesis Method for Au, Pd, and Pt Aerogels Via Direct Solution-Based Reduction

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various precursor noble metal ions with reducing agents in a 1:1 (v/v) ratio results in the formation of metal gels within seconds to minutes compared to much longer synthesis times for other techniques such as sol-gel. Conducting the reduction step in a microcentrifuge tube or small volume conical tube facilitates a proposed nucleation, growth, densification, fusion, equilibration model for gel formation, with final gel geometry smaller than the initial reaction volume. This method takes advantage of the vigorous hydrogen gas evolution as a by-product of the reduction step, and as a consequence of reagent concentrations. The solvent accessible specific surface area is determined with both electrochemical impedance spectroscopy and cyclic voltammetry. After rinsing and freeze drying, the resulting aerogel structure is examined with scanning electron microscopy, X-ray diffractometry, and nitrogen gas adsorption. The synthesis method and characterization techniques result in a close correspondence of aerogel ligament sizes. This synthesis method for noble metal aerogels demonstrates that high specific surface area monoliths may be achieved with a rapid and direct reduction approach.

Fuel cell powered small unmanned aerial systems (UASs) for extended endurance flights

Small unmanned aerial systems (UASs) have been used for military applications and have additional potential for commercial applications [1-4]. For the military, these systems provide valuable intelligence, surveillance, reconnaissance and target acquisition (ISRTA) capabilities for units at the infantry, battalion, and company levels. The small UASs are light-weight, manportable, can be hand-launched, and are capable of carrying payloads. Currently, most small UASs are powered by lithium-ion or lithium polymer batteries; however, the flight endurance is usually limited less than two hours and requires frequent battery replacement. Long endurance small UAS flights have been demonstrated through the implementation of a fuel cell system. For instance, a propane fueled solid oxide fuel cell (SOFC) stack has been used to power a small UAS and shown to extend mission flight time. The research and development efforts presented here not only apply to small UASs, but also provide merit to the viability of extending mission operations for other unmanned systems applications.