2, Armament Research, Development, and Engineering Center, Picatinny Arsenal, New Jersey, United States
Noble metal aerogels that possess high surface area and tunable porosity offer a wide range of catalytic applications. Control over monolith shape, pore size, and ligament diameter is desired in order to tune device integration, electrolyte mass transport properties, electronic conductivity, and mechanical robustness. Aerogel synthesis techniques such as solvent mediated aggregation, linker molecules, sol–gel, hydrothermal, and carbothermal reduction do not offer synthesis control over all desired material properties. Here we present the synthesis of palladium and platinum aerogels using gelatin and carboxymethyl cellulose nanofiber biotemplates for catalysis that provides control over aerogel shape, pore size, conductivity, and elastic modulus. Biotemplate hydrogels were formed via covalent cross linking using glutaraldehyde for gelatin, and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) with a diamine linker molecule for carboxymethylated cellulose nanofibers. Biotemplate hydrogels were incubated in precursor palladium and platinum salts, reduced with sodium borohydride, and rinsed. Final aerogel structures were achieved using super critical point drying. Scanning electron microscopy indicated contiguous three dimensional nanowire structures for both gelatin and carboxymethyl cellulose biotemplated nanowires, and X-ray diffractometry confirmed metal content with no oxide peaks. Gas adsorption, impedance spectroscopy, and cyclic voltammetry were correlated to determine aerogel surface area. A four point probe was used to determine electronic conductivity, and atomic force microscope nanoindentation was used to determine material elastic moduli. Platinum and palladium aerogel catalysis was evaluated for hydrogen adsorption and desorption in 0.5M H2SO4. These self-supporting biotemplated palladium and platinum aerogels are envisioned to offer a flexible synthesis scheme to control shape, porosity, electrical conductivity, and mechanical robustness catalytic, sensing, and energy applications.