Synthesis and electrochemical performance of bio-derived activated carbon from agricultural waste for supercapacitor applications

Project Abstract

Bio-derived activated carbon (BAC) with tailored porosity was synthesized from agricultural waste via a low-temperature carbonization followed by chemical activation using potassium hydroxide to produce a high surface area and hierarchical pore structure. The study investigates how precursor selection, activation ratio, and thermal treatment influence textural properties, surface chemistry, and electrochemical performance in aqueous and organic electrolyte configurations. Comprehensive characterizations including N2 adsorption-desorption isotherms, Raman spectroscopy, X-ray diffraction, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and X-ray Photoelectron Spectroscopy (XPS) were employed to elucidate the relationship between micro-, meso-, and macroporosity and electrochemical behavior. The BAC samples exhibited specific surface areas ranging from 1200 to 2600 m2/g and predominantly microporous structures with interconnected mesopores that facilitate rapid ion transport and high charge storage. Electrochemical performance was evaluated in a three-electrode setup and symmetric supercapacitor configurations using aqueous (KOH) and organic (TEABF4 in acetonitrile) electrolytes. Cyclic voltammetry (CV) indicated quasi-rectangular profiles with minimal distortion at scan rates up to 200 mV/s, while galvanostatic charge-discharge (GCD) demonstrated high reversible capacitance retention at varying current densities. The best-performing BAC delivered a specific capacitance of up to 550 F/g in alkaline aqueous electrolyte at 1 A/g, with excellent cycling stability showing >95% capacitance retention after 10,000 cycles. In organic electrolyte, a capacitance of approximately 260 F/g was achieved at 1 A/g with 92% retention after 5,000 cycles, benefiting from wider voltage windows and robust electrical conductivity of the carbon framework. Electrochemical impedance spectroscopy (EIS) revealed low internal resistance and favorable proton/spillover transport within the hierarchical pore network, enabling rapid ion diffusion and high-rate capability. Pseudocapacitive contributions from surface functionalities (e.g., –C=O, –OH groups) identified by XPS and Fourier-transform infrared spectroscopy (FTIR) were correlated with enhanced capacitance, particularly at higher scan rates, while both the degree of graphitization and defect density influenced electronic conductivity and stability. A systematic comparison of lignocellulosic precursors demonstrated that higher lignin content yielded more robust mesopore development and better rate performance due to improved pore connectivity and chemical stability under activation conditions. The study also monitored ash content and inorganic residue as potential performance modifiers, confirming that optimized carbonization temperatures (600–700 °C) and KOH-to-biomass ratios (12 to 13) produce a balanced pore structure and surface chemistry. The findings indicate that BAC derived from agricultural waste can rival commercial activated carbons in specific capacitance while offering sustainable, low-cost production pathways. The work discusses scalability considerations, environmental impacts, and potential strategies to tailor pore architecture for targeted energy storage applications, including hybrid devices and flexible supercapacitors. Overall, the research demonstrates a clear link between precursor characteristics, activation protocol, pore structure, surface chemistry, and electrochemical performance, providing a viable route to high-performance, bio-based supercapacitors with reduced ecological footprint.

Project Overview

What This Project Is About

---

A straightforward exploration of turning agricultural waste into activated carbon, and testing how well it can store and deliver electrical energy in supercapacitors. The project looks at a simple, real-world way to reuse waste materials to make a performance-ready energy storage material.

---

---

The Problem It Addresses

---

A large amount of agricultural waste is produced every year, often burned or disposed of, which causes pollution. Conventional activated carbon can be expensive or rely on non-renewable sources. This project seeks a low-cost, eco-friendly alternative that also improves energy storage devices.

---

---

Objectives of the Project

---

1. Convert agricultural waste into activated carbon using a simple chemical process.
2. Characterize the material’s surface and structure to understand how it could store charge.
3. Test the material in a basic supercapacitor setup to measure energy storage and power delivery.
4. Compare performance with a standard carbon sample to assess improvements or gaps.
5. Evaluate environmental and economic benefits of the approach.

---

---

What You Will Do Step by Step

---

Identify suitable agricultural waste (e.g., husks or shells) and prepare it for processing. Convert the waste to activated carbon with a simple activation method. Analyze surface area and porosity using basic lab tools. Assemble a small supercapacitor test cell and record charge/discharge data. Analyze results to determine capacitance and stability, and compare with a reference carbon.

---

---

Expected Outcome

Anticipated findings include a viable, low-cost activated carbon from waste, capable of storing a meaningful amount of charge with good stability, showing competitive performance compared to conventional materials. The project should demonstrate feasibility and potential environmental and economic benefits.