(163n) Salt-Templated Transition Metal and Metal Oxide Aerogels

F. John Burpo*, Enoch A. Nagelli, Alexa S. Zammit, Felita W. Zhang, Veronica M. Lucian, Edward M. Tang

Department of Chemistry and Life Science, United States Military Academy, West Point, NY 10996, USA

*Corresponding: F. John Burpo, Email: john.burpo@westpoint.edu

Transition metal aerogels are utilized in a diverse array of applications ranging from sensors to energy storage and catalysis due to their high surface area and ability to tune reaction specificity through the variation of metal composition. The ability to synthesize these materials as three-dimensional porous nanostructures enables control of surface area, pore size and mass transfer properties, electronic conductivity, and ultimately device integration. In general, 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 mass transfer. High energy requirements, limited scalability, and poor shape control present challenges to prepare transition metal aerogels. Insoluble salts offer a template approach to synthesize of a range of porous metal structures. Magnus’ salt needles formed from the combination of oppositely charged square planar ions have served as templates that are chemically reduced to form porous macrotube, macrobeam, and nanofoam structures. This approach has been demonstrated for Pt, Pd, Pt-Pd, Cu-Pt, Au-Cu, and Au-Cu-Pd salts and resulting porous metal structures.^1-4 In this work, we generalize the salt-templating synthesis method to transition metal salts of CuSO₄, NiSO₄, and FeCl₃ chemically reduced with NaBH₄ to form Cu/CuO, Ni/NiO and Fe/FeO metal gels that are rinsed in deionized water, solvent exchanged in ethanol, and supercritically dried to form aerogels. Resulting aerogel monoliths are characterized with x-ray diffractometry, scanning electron microscopy, energy dispersive x-ray spectroscopy, nitrogen gas adsorption-desorption, 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.

References

1. F. John Burpo, Enoch A. Nagelli, Stephen J. Winter, Joshua P. McClure, Stephen F. Bartolucci, Alvin R. Burns, Sean F. O’Brien. “Salt-Templated Hierarchically Porous Platinum Macrotube Synthesis.” ChemistrySelect. 2018, 3, 4542-4546.
2. F. John Burpo, Enoch A. Nagelli, Lauren A. Morris, Kamil Woronowicz, Alexander N. Mitropoulos. “Salt-Mediated Au-Cu Nanofoam and Au-Cu-Pd Porous Macrobeam Synthesis.” Molecules. 2018, 23, 1701-1715.
3. F. John Burpo, Enoch A. Nagelli, Stephen F. Bartolucci, Alexander N. Mitropoulos, Joshua P. McClure, David R. Baker, Anchor R. Losch, Deryn Chu. “Salt-Templated Platinum-Palladium Porous Macrobeam Synthesis.” MRS Communications, 2019, 9, 280-287.
4. F. John Burpo, Enoch A. Nagelli, Anchor R. Losch, Jack Bui, Gregory T. Forcherio, David R. Baker, Joshua P. McClure, Stephen F. Bartolucci, Deryn D. Chu. “Salt-Templated Platinum-Copper Porous Macrobeams for Ethanol Oxidation.” Catalysts, 2019, 9, 662.