Abstract

Preparing sustainable and highly efficient biochars as electrodes remains a challenge for building green energy storage devices. In this study, efficient carbon electrodes for supercapacitors were prepared via a facile and sustainable single-step pyrolysis method using spruce bark as a biomass precursor. Herein, biochars activated by KOH and ZnCl2 are explored as templates to be applied to prepare electrodes for supercapacitors. The physical and chemical properties of biochars for application as supercapacitors electrodes were strongly affected by factors such as the nature of the activators and the meso/microporosity, which is a critical condition that affects the internal resistance and diffusive conditions for the charge accumulation process in a real supercapacitor. Results confirmed a lower internal resistance and higher phase angle for devices prepared with ZnCl2 in association with a higher mesoporosity degree and distribution of Zn residues into the matrix. The ZnCl2-activated biochar electrodes’ areal capacitance reached values of 342 mF cm−2 due to the interaction of electrical double-layer capacitance/pseudocapacitance mechanisms in a matrix that favors hydrophilic interactions and the permeation of electrolytes into the pores. The results obtained in this work strongly suggest that the spruce bark can be considered a high-efficiency precursor for biobased electrode preparation to be employed in SCs.

Highlights

  • The development of sustainable and efficient energy storage systems (ESS) attracts massive attention in the literature due to their wide range of applications, from portable electronic devices to hybrid electric vehicles [1–3]

  • specific surface area (SSA) and porosity of the biobased carbon materials are essential properties that strongly influence their performance as materials regardless of their applications [2,3]

  • This hysteresis was observed in both samples, which characterizes mesoporous materials describes an adsorption process resulting in micropores filling

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Summary

Introduction

The development of sustainable and efficient energy storage systems (ESS) attracts massive attention in the literature due to their wide range of applications, from portable electronic devices to hybrid electric vehicles [1–3]. Among different types of ESS, supercapacitors (SCs) have favorable properties of relatively high specific power density (10 to 100,000 W/kg), outstanding cycling stability (minimal change in the electrochemical response after a few thousands of reuses), low resistance, fast charge/discharge, and a wide range of applications [4,5]. EDLCs make use of the diffusion and accumulation of double-layer charges formed by the adsorption of electrolyte ions on the electrode’s surface (physisorption); electrodes with very high specific surface area (SSA) and a high level of hydrophilicity are generally required to fabricate EDLCs [3,4]. Pseudocapacitors store energy through the formation of an EDL and through reversible redox reactions with the fast insertion of the electrolyte ions onto the surface layer of the electrode [3,4].

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