(167c) Salt-Templated Metal and Metal Oxide Porous Materials

F. John Burpo*, Enoch A. Nagelli, Anchor R. Losch, Jack Bui, Felita Zhang, Veronica Lucian, Brittany Aiken, Epiphanie Donkeng

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

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

Metal, multi-metallic and alloy nanomaterials enable a broad range of catalytic applications with high surface area and tuning 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. Discrete and aggregated nanoparticles offer tremendous design flexibility, yet methods to assemble them into extended 3-dimensional structures suffer from a number of limitations, especially aggregation and diffusion times. Insoluble salts offer a template approach to synthesize of a range of porous metal structures. Magnus and Vauquelin salt needles formed from the combination of oppositely charged square planar ions serve as templates that are electrochemically reduced to form porous macrotube 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 Platinum macrotubes with square cross-section and porous sidewalls composed of fibril textured nanoparticles are synthesized from high aspect ratio insoluble Mangus’ salt needles in a single reduction step.¹ Macrotubes 10’s to 100’s of micrometers long pressed into free-standing films exhibit a specific capacitance of 18.5 F/g and a solvent accessible specific surface area of 61.7 m²/g. Porous platinum–palladium macrobeams are templated from high aspect ratio Magnus’ salt needle derivatives resulting from the combination of [PtCl₄]^2- and/or [PdCl₄]^2- with [Pt(NH₃)₄]²⁺ ions with salt needles ranging from 15 to 300 μm in length.³ Electrochemical reduction of the salt templates results in porous macrobeams with a square cross-section. Porous side wall texture and elemental composition was controlled with initial platinum to palladium salt ratio. Macrobeam free-standing Pt-Pd films exhibited a specific capacitance up to 11.73 F/g and a solvent accessible surface area of 26.6 m²/g. Cu-Pt macrobeams, Au-Cu nanofoams, and Au-Cu-Pd macrobeams were synthesized from salt precursors in the same manner.² 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. 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. 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. 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(1), 280-287.