Magnetic-Field-Assisted Fe Nanowire Conformable Aerogels Galvanically Displaced to Cu and Pt for Three-Dimensional Electrode Applications

There is an increasing need for free-standing, conformal electrodes for practical energy storage devices. To address this, we demonstrate the magnetic-field-assisted synthesis of interpenetrating Fe nanowire (FeNW) gels without the use of templates or composite scaffold material over a range of magnetic fields. In either a wet gel or a supercritical dried state as an aerogel, the FeNWs may be pressed into thin or conformal films. Varying the applied magnetic field strength with a solenoid during chemical synthesis resulted in increased nanowire length and local orientation of the FeNWs with increasing magnetic field strength, with approximately 80 nm diameters across field strengths of 0-150 mT. Flowing K₂PtCl₄ or CuSO₄·5H₂O solutions through the wet iron gels to achieve the near complete galvanic displacement of iron to the more noble [PtCl₄]^2- and Cu²⁺ ions resulted in either platinum nanotubes (PtNTs) or copper nanowires (CuNWs) while maintaining a percolating network structure. Similar to the FeNW gels, the PtNT and CuNW gels were able to be supercritical dried and/or pressed into thin or conformal electrode films. CuNW and PtNT films demonstrated good potential as capacitive and oxygen reduction reaction electrodes, respectively. The magnetic-field-assisted synthesis of ferromagnetic iron nanowires offers a simple, rapid, and tunable method that, when combined with galvanic displacement with more noble metal ions, may enable a wide range of metal, alloy, and multimetallic nanowires and nanotubes for energy storage, sensing, and catalytic applications.