Nanodiamond-Based Separators for Supercapacitors Realized on Paper Substrates

In response to the request for sustainable high performance energy storage devices, a significant interest is focused on developing environmentally friendly supercapacitors. In this context, cellulose-based substrates for energy storage devices can be well-engineered, lightweight, safe, thin, and flexible. Herein, a scalable, low-cost, and easy-to-process approach for the preparation of supercapacitors using large area techniques like spray and blade coating is presented. Following a green strategy, all components are chosen or formulated in water-based dispersions. Symmetric supercapacitors using common copy paper and electronic paper as the substrate, and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as electrodes, are realized and investigated. The novelty of this work consists of the use of composites based on detonation nanodiamonds (DNDs) and hydroxypropyl cellulose (HPC) as a solid-state electrolyte and separator. Devices with solution electrolyte using the same HPC + DND composite but with the addition of sodium sulfate are prepared. The performance obtained using solid electrolyte (HPC + DNDs) and liquid electrolyte (HPC + DNDs + Na₂SO₄) on both substrates is comparable in terms of specific capacitance: ≈0.13 – 0.52 F g⁻¹ for (HPC + DNDs) and ≈0.35 – 0.82 F g⁻¹ for (HPC + DNDs + Na₂SO₄), with power density in the range of ≈19 – 24 μW cm⁻².