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

Abstract

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.