Eco-friend air electrode for flexible quasi-solid-state electrolyte zinc-air battery based on spherical glucose biochar derived from biorefinery process

Biorefinery using waste biomass is a key technology for sustainable development and is widely used in renewable energy production. However, biorefineries for energy storage applications have rarely been studied. In this study, a zinc-air battery (ZAB), which is one of the eco-friendlier energy storage devices, is proposed using the biorefinery process. The spherical glucose biochar (SGBC) was produced by a two-step process. The first step was the saccharification which included NaOH pretreatment and enzymatic hydrolysis. The second step was the carbonization including hydrothermal reactions and carbonization. The SGBC/MnO₂/poly(3,4-ethylenedioxythiophene) (PEDOT) composite (SMP) was produced by in-situ polymerization with Fe(ClO₄)₃. The SMP exhibited excellent oxygen reduction reactions (ORR) and oxygen evolution reaction (OER) comparable to Pt/C due to the complementary effects of each component. Therefore, the fabricated flexible quasi-solid-state electrolyte SMP-based ZAB (SMP-ZAB) displayed high performance. The SMP-ZAB exhibited a peak power density of 101.2 mW/cm³. The discharge was maintained for 9.6 h at 5 mA/cm³ and the charge-discharge cycle was maintained for 16 h without remarkable potential change (5 min each for charge and discharge at 5 mA/cm³). In addition, the SMP-ZAB could theoretically produce 9540 cells from 1000 g of chestnut shell (CNS), demonstrating the potential of mass production for industrial-scale production (electrode area: 4 cm²). These results suggest that the SMP-ZAB could be applied as a future wearable energy device with an eco-friendly process.