Cellulose Nanofiber-Carbon Nanotube Composite Nickel/Nickel Oxide Multi-Functional Aerogels

Multi-functional materials that offer both mechanical structure and electrochemical or electromagnetic functionality for energy storage and/or sensor capabilities will be critical as technology platform development continues to miniaturize and place a higher premium on system volume and mass constraints. Most material development demonstrations focus on a single performance metric such as mass specific energy storage or elastic modulus. To address the need for low-cost, scalable multi-functional materials, we demonstrate the assembly of cellulose nanofiber biopolymer templates with carbon nanotubes for a composite scaffold to host a nickel aerogel phase. This ternary material composite allows the tuning of properties such as material phase composition, nanoscale feature size, pore structure, conductivity, electrochemical capacitance, magnetic response, and mechanical stiffness. Previous demonstrations of this approach with biopolymers to control nanostructure and functionality include bio-templated gelatin, silk fibroin, and cellulose nanofiber composite metal aerogels.^1-4 Biopolymers allow nanostructure shape control and inclusion of chemical functional groups to mediate metal phase deposition, and the combined assembly of carbon nanotubes allows for the increase of electrical and thermal conductivity. Here, we demonstrate the synthesis of a porous, mechanically strong composite aerogel with tunable pore size, nanowire length, diameter, and material phase. This approach enables electro-magneto-mechanical materials that can enable device development at multiple length scales with the potential for an overall decrease of objective system mass and corresponding improvement in performance metrics. The assembly of carboxymethyl cellulose nanofiber-carbon nanotubes (CNF-CNT) into a composite hydrogel is followed by equilibration with a nickel salt solution and chemical reduction. Subsequent rinsing, solvent exchange and supercritical drying results in a composite aerogel. Pyrolysis and thermal annealing of the aerogel yields a porous nickel oxide aerogel. 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, and compressive stress. Electrochemical performance was determined with electrochemical impedance spectroscopy and cyclic voltammetry. The composite CNF-CNT-metal/metal oxide aerogels are envisioned to provide multi-functional material solutions to range of energy storage, catalytic, and fuel-cell applications.

References
¹ Burpo, F.J., Mitropoulos, A., Nagelli, E., Ryu, M., Palmer, J. Gelatin Biotemplated Pt Aerogels. MRS Advances, 2018, 3(47-48), 2875-2880.
² Mitropoulos, A., Burpo, F.J., Nguyen, C., Nagelli, E., Ryu, M., Wang, J., Sims, R., Woronowicz, K., Wickiser, J. Noble metal composite porous silk fibroin aerogel fibers. Materials, 2019, 12(6) 894.
³ Burpo, F.J., Mitropoulos, A., Nagelli, E., Palmer, J., Morris, L., Ryu, M., Wickiser, J. Cellulose Nanofiber Biotemplated Palladium Aerogels. Molecules. 2018, 23, 1405-1418.
⁴ Zhang, F., Trackey, P., Verma, V., Mandes, G., Calabro, R., Presot, A., Tsay, C., Lawton, T., Zammit, A., Tang, E., Nguyen, A., Munz, K., Nagelli, E., Bartolucci, S., Maurer, J., Burpo, F.J. Cellulose Nanofiber-Alginate Biotemplated Cobalt Composite Multifunctional Aerogels for Energy Storage Electrodes. 2023, Gels, 9(11), 893