With the rapid development of global economy, the depletion of fossil fuels, and the severe environmental pollution, new electrochemical energy storage technologies are in urgent need. In recent years, supercapacitors have attracted extensive attention due to their advantages of high power density, long cycle life, wide working temperature window, and excellent cycling stability. Unfortunately, traditional supercapacitor devices are big and heavy, complicated to manufacture, and most of the time undegradable, and therefore cannot achieve sustainable development goals of the society. In this content, it is imperative to develop an innovative type of flexible and environmental friendly supercapacitor. Polyaniline-polylactic acid (PANI-PLA) biodegradable flexible supercapacitor electrode was prepared by in situ chemical polymerization method utilizing polylactic acid (PLA) film as the substrate. Scanning electron microscope (SEM), Fourier infrared spectrum (FTIR), and ultraviolet visible spectrophotometry (UV-Vis) were performed to characterize the morphology and chemical structure of the electrode. The electrochemical tests show that under the three-electrode system, the areal specific capacitance of PANI-PLA can reach 5.00 mF·cm−2 (@0.10 mA·cm−2). Under the two-electrode system employing polyvinyl alcohol/sulfuric acid (PVA/H2SO4) as the gel electrolyte, the symmetric PANI-PLA//PANI-PLA solid supercapacitor delivers an areal capacitance of 0.20 mF·cm−2, a power density of 3.60 μW·cm−2, and a corresponding energy density of 0.02 μWh·cm−2 (@0.004 mA·cm−2). The asymmetric solid supercapacitor consisting of polyaniline grown on stainless steel (PANI-SS) and PANI-PLA delivers an areal capacitance of 23.33 mF·cm−2, a power density of 30.09 μW·cm−2, and a corresponding energy density of 1.17 μWh·cm−2 (@0.05 mA·cm−2).

In order to meet the increasing requirements of wearable electronic devices, low-cost, high-performance flexible supercapacitors have become a research hotspot. In this work, flexible, self-standing PANI-CHF-GEL electrode was obtained by growing polyaniline (PANI) on the surface of corn husk fiber (CHF) and mixed with polyvinyl alcohol/sulfuric acid (PVA/H2SO4) gel, followed by a facile frozen-thawing method. PANI-CHF-GEL exhibits excellent mechanical properties (a fracture strength of 259 kPa at a fracture strain of 121%) and good toughness (a fracture energy of 0.167 MJ·cm−3). Employing PVA/H2SO4 as the gel electrolyte, the symmetric PANI-CHF-GEL//PANI-CHF-GEL solid supercapacitor delivers an areal capacitance of 1789.74 mF·cm−2, a power density of 0.34 mW·cm−2, and a corresponding energy density of 3.51 mWh·cm−2 (@3.00 mA·cm−2). Moreover, the device retains its original properties even bent 90°, indicating its promise potentials for wearable electronics.

Polylactic acid (PLA) has promising potentials for transient electronic applications due to its biodegradability and biocompatibility, which is expected to help alleviate electronic waste disposal problems. Recently, PLA has been used as the polymer substrate to fabricate green and flexible supercapacitors (SCs). However, the intrinsic fracture textile and limited electroactive materials deposited on the PLA substrate resulting in poor energy storage performance still remain challenging. Herein, a facile approach has been proposed to prepare flexible, yet robust electrodes of polyaniline coated on foamed PLA (PANI-fo-PLA). Aniline monomers were directly polymerized on the porous foamed PLA (fo-PLA) which was prepared via a simple nonsolvent-induced-phase-separation (NIPS) method. The fo-PLA endows the PANI-fo-PLA electrode with superior flexibility (a fracture strain of 34.70%) and high mechanical strength (a fracture strength of 77.80 MPa) which are significantly higher than those values of solvent-cast PLA films; meanwhile, the porous structure provides rich sites for the growth of PANI, which thus significantly increases the loadings of electroactive materials, and facilitates the ion transportation during the energy storage process. Employing PVA/H2SO4 as the gel electrolyte, the symmetric PANI-fo-PLA//PANI-fo-PLA SC delivers a high areal capacitance of 27.73 mF cm−2 (@0.05 mA cm−2), which is more than one hundred times higher than that of the SC based on electrodes of PANI grown on non-porous PLA film. The SC retains 66.29% of its original capacitance even bent at 90°, demonstrating its great potentials for flexible wearable electronics. Moreover, the PANI-PLA can be readily degraded in alkaline solutions within 2 h under sonication. This work paves the way to fabricate flexible, transient, and high performance energy storage devices from PLA. A flexible, robust, and degradable PANI-fo-PLA electrode with high electrochemical energy storage performance has been prepared via a both time- and energy- saving approach.

To fabricate high performance energy storage devices with low cost, this study proposed a facile method to prepare biomass-based hierarchical activated carbon-polyaniline composites (HAC-PANI) via an in-situ chemical polymerization method, and their applications in supercapacitors (SCs) and zinc-ion hybrid supercapacitors (ZHSCs) were investigated. The results show that hierarchical porous structure and high specific area of HAC provide growth sites for PANI and effectively reduce the agglomeration of PANI; and meanwhile promote the transport of electrolyte ions, and degrease the charge transfer resistance. When the mass ratio of biomass-based hierarchical activated carbon (HAC) to aniline monomer (An) is 1∶2, uniform PANI nanoparticles were observed growing on HAC, and the resulting composite (HAC-2PANI) electrode exhibits the optimum performance. Under the three-electrode system, the mass specific capacitance of HAC-2PANI reaches as high as 415.6 F·g−1 (@1 A·g−1). The HAC-2PANI based all-solid supercapacitor (s-HAC-PANI-SC) displays a specific capacitance of 217.4 F·g−1 (@1 A·g−1), an energy density of 26.5 W·h·kg−1 and a power density of 1875.0 W·kg−1. The zinc-ion hybrid supercapacitor (HAC-PANI-ZHSC) constructed with HAC-2PANI as the cathode and zn foil as the anode exhibits a high specific capacity of 91.8 mA·h·g−1 (@0.2 A·g−1), a remarkable energy density of 64.3 W·h·kg−1, and a power density of 140.0 W·kg−1, indicating promising potentials of biomass-based carbon composites for high performance and low cost electrochemical energy storage devices.