A chitosan/poly(ethylene glycol)-ran-poly(propylene glycol) blend as an eco-benign separator and binder for quasi-solid-state supercapacitor applications

Abstract

Herein, activated porous carbon (ACTS-900) derived from Tamarindus indica, a bio-source, via KOH activation and carbonization at 900 °C was used as an active electrode material for supercapacitor (SC) applications. In the three-electrode configuration, ACTS-900 shows the maximum specific capacitance (C_s,3E) of 225 F g⁻¹ at 50 mV s⁻¹ and 249 F g⁻¹ at 0.5 A g⁻¹ in 1 M H₂SO₄. A high-performance, bio-based, environmentally benign and cost-effective chitosan/poly(ethylene glycol)-ran-poly(propylene glycol) [Ch/poly(EG-ran-PG)]-based polymer blend was employed as a membrane-cum-separator as well as a green binder in the electrodes. The blend polymer membrane was prepared by mixing chitosan (Ch) and poly(EG-ran-PG) in a 1 : 1 weight ratio in a 1% aqueous acetic acid solution followed by drying under controlled evaporation. The blend membrane showed high porosity (2 μm–7 μm diameter pores) and excellent thermal (up to 250 °C), chemical (in 1 M H₂SO₄), electrochemical (up to 1.21 V) and mechanical stability (up to 39 MPa under tensile loading). The performance of a symmetric two-electrode SC device was evaluated using a H₂SO₄-(1 M)-soaked-Ch/poly(EG-ran-PG) membrane and ACTS-900 active electrode materials. The obtained results were compared with those obtained using commercially available binders and membranes. The single electrode specific capacitances (C_s,_2E) in the symmetrical SC device were 193 F g⁻¹ at 50 mV s⁻¹ and 132 F g⁻¹ at 2 A g⁻¹ with H₂SO₄-(1 M)-soaked-Ch/poly(EG-ran-PG) as the membrane and binder. The maximum energy density and power density of the SC device are 4.7 W h kg⁻¹ (at 1 A g⁻¹) and 2.5 kW kg⁻¹ (at 5 A g⁻¹), respectively. Due to the superior wetting properties of the blend membrane and binder, excellent capacity retention was observed (∼99%) over 6000 cycles at the current density of 3.5 A g⁻¹. As a proof-of-concept, a red light-emitting diode was illuminated using three serially connected 3 V SC stacks.