Multifunctional metal-free rechargeable polymer composite nanoparticles boosted by CO<inf>2</inf>

Herein, we present a multigram scale-up route for the preparation of novel polymer composite nanoparticles as potential multifunctional rechargeable material for future, sustainable batteries. The nanoparticles (20 nm) comprise three innocuous yet functional interpenetrated macromolecular networks: polypyrrole, methylcellulose, and lignin. They are uniquely assembled in strands or chains (~200 nm) such as necklace beads and show long-term stability as water dispersion. We find that an aqueous suspension of this hierarchical nanomaterial shows two sets of reversible redox peaks, separated by ~600 mV, originating from the catechol moieties present in the lignin biopolymer. Remarkably, the addition of carbon dioxide increased the capacity of one of the redox processes by 500%. Importantly, the three redox stages occur in the presence of the same nanostructured polymer so being a potentially bifunctional material to be used in advanced electrochemical systems. The new properties are attributed to an intrinsic chemical and electronic coupling at the nanoscale among the different building blocks of the metal-free polymer composite and the structural rearrangement of the interpenetrated polymer network by the incorporation of CO2. We have provided both a new electrochemically multifunctional hierarchically structured material and a facile route that could lead to novel sustainable energy applications.