Electropolymerization-Induced NbOPO₄ Nanoparticle Electrodeposition for Hybrid Supercapacitors

The formation of thin films made of functionalized nanoparticles is relevant to different areas, such as energy storage. Batteries and supercapacitors usually require the addition of different materials, e.g., binders, that do not contribute to the capacity. Here, we present an approach that is based on the electropolymerization of a charge transfer adduct formed between EDOT, a monomer of the conducting polymer PEDOT, and niobium oxyphosphate, NbOPO₄, synthesized nanoparticles. To improve the energy storage performance of the deposit, carbon nanotubes, CNTs, were added to the dispersion and electrochemically codeposited to form a binder-free NbOPO₄/PEDOT/CNT film. The latter exhibits a better synergetic performance than pure NbOPO₄ and provides 210 F g^-1 at 1 A g^-1 (110 mF cm^-2 at 1 mA cm^-2) while retaining 81% of the capacitance at 5 A g^-1. The capacity could be further increased to 347 F g^-1 at 1 A g^-1 by optimizing the ratio between the three components. This work is an important extension of our “Nano to Nano” approach, which aims at depositing nanomaterials from their dispersion by an external mild electrochemical stimulus.