Salt-Templated Metal and Metal Oxide Porous Materials

Pure metal, multi-metallic and alloy nanomaterials enable a broad range of catalytic applications with high surface area and tunable reaction specificity through the variation of metal composition. Synthesizing these materials as three-dimensional porous nanostructures enables control of surface area, pore size and mass transfer properties, electronic conductivity, and ultimately device integration. Discrete and aggregated nanoparticles offer tremendous design flexibility, yet methods to assemble them into extended 3-dimensional structures suffer from several limitations, especially aggregation and diffusion times. Insoluble salts offer a template approach to synthesize of a range of porous noble and transition metal structures and monoliths. Chemical reduction of insoluble Magnus and Vauquelin salt needles formed from the combination of oppositely charged square planar platinum, palladium, gold, and copper ions have been previously demonstrated as templates for mesoporous macrobeam and macrotubes 10’s to 100’s of micrometers long with square cross-sections ranging from approximately 100 nm to 3 µm.^1-4 The use of insoluble noble metal salt templates was extended to the chemical reduction of copper and nickel transition metal poly-crystalline salts. After chemical reduction, metal gels were rinsed, solvent exchanged in ethanol, and supercritical dried in CO₂ to form aerogels. Metal and metal oxide phase composition varied depending on the sulfate, acetate, and chloride salt template anion. Aerogels were characterized using scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffractometry, nitrogen gas adsorption-desorption with and Brunauer-Emmett-Teller surface area analysis, vibrating-sample magnetometry, magnetic force microscopy, and nanoindentation. Electrochemical performance of copper and nickel oxide aerogels as pseudocapacitors was determined with electrochemical impedance spectroscopy and cyclic voltammetry. The use of salt precursors is envisioned as a synthesis route to a wide range of metal and multi-metallic nanostructures for catalytic, energy storage, and sensing applications.<br/><br/><b>References</b><br/>Burpo, F.J., Nagelli, E., Winter, S., McClure, J., Bartolucci, S., Burns, A., O’Brien, S. “Salt-Templated Hierarchically Porous Platinum Macrotube Synthesis.” <i>ChemistrySelect</i>. 2018, <i>3</i>, 4542-4546.<br/>Burpo, F.J., Nagelli, E., Morris, L., Woronowicz, K., Mitropoulos, A. “Salt-Mediated Au-Cu Nanofoam and Au-Cu-Pd Porous Macrobeam Synthesis.” <i>Molecules</i>. 2018, <i>23</i>, 1701-1715.<br/>Burpo, F.J., Nagelli, E., Bartolucci, S., Mitropoulos, A., McClure, J., Baker, D., Losch, A., Chu, D. “Salt-Templated Platinum-Palladium Porous Macrobeam Synthesis.” <i>MRS Communications</i><i>, </i>2019, 9(1), 280-287.<br/>Burpo, F.J., Nagelli, E.A., Losch, A.R., Bui, J., Forcherio, G.T., Baker, D.R., McClure, J.P., Bartolucci, S.F., Chu, D.D. Salt-Templated Platinum-Copper Porous Macrobeams for Ethanol Oxidation. <i>Catalysts,</i> 2019, <i>9</i>(8), 662.