Synthesis and characterisation of bio-derived porous carbon for high-performance supercapacitors via hydrothermal carbonization and activation.

Project Abstract

Porous carbon materials derived from biomass were synthesized using a two-step approach hydrothermal carbonization (HTC) to convert agricultural waste into hydrochar, followed by chemical activation with potassium hydroxide (KOH) and subsequent thermal treatment to develop a hierarchical porosity. The primary objective was to achieve high specific surface area, tailored pore size distribution, and robust electrochemical performance suitable for high-power supercapacitors. The HTC process was optimized by varying temperature (180–220 °C) and residence time (6–24 h) to maximize CO2 and H2O release while preserving activating sites on the carbon matrix. Post-HTC activation used a KOH-to-char ratio of 21 and activation temperatures in the range of 700–850 °C under inert atmosphere to promote microporosity while enabling connectivity to mesopores for facile ion transport. Comprehensive characterisation included N2 adsorption-desorption isotherms (BET surface area, pore volume distribution via DFT and NLDFT methods), X-ray diffraction (XRD) to assess graphitic ordering, Raman spectroscopy to evaluate disorder and defect density (I_D/I_G ratio), Fourier-transform infrared spectroscopy (FTIR) for surface functional groups, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for morphological insights, and thermogravimetric analysis (TGA) for thermal stability. Electrochemical performance was evaluated in a symmetric aqueous electrolyte (e.g., 1 M H2SO4) and in an organic electrolyte (e.g., 1 M TEABF4 in acetonitrile) to compare rate capability and operating voltage windows. In a three-electrode configuration, specific capacitance, rate capability, and cycling stability were measured by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). The bio-derived porous carbons demonstrated specific surface areas ranging from 800 to over 1500 m²/g, with a hierarchical pore structure comprising predominantly micropores (<2 nm) for charge storage and interconnected mesopores (2–50 nm) to accelerate ion transport. The best samples achieved specific capacitances between 250 and 380 F/g at 0.5 A/g in aqueous electrolytes and 180–260 F/g at 2–5 A/g in organic electrolytes, with capacitance retentions above 90% after 10,000 cycles in aqueous media and substantial stability in organic media. EIS revealed low charge-transfer resistances and favorable Warburg diffusion characteristics, indicating efficient ion diffusion within the porous network. The role of surface functional groups (hydroxyl, carbonyl, and carboxyl moieties) was probed via XPS and FTIR, revealing that heteroatom enrichment modestly enhances pseudocapacitance contributions and stabilizes the solid-electrolyte interface. Temperature-dependent activation studies indicated an optimal window (around 750–800 °C) that balances porosity development with structural integrity. A comparative life-cycle energy and environmental impact assessment showed reduced embodied energy and waste streams relative to conventional activated carbon production, underscoring the sustainability advantages of using agricultural waste streams. The study demonstrates that controlled HTC pretreatment combined with optimized chemical activation can yield bio-derived porous carbons with tunable pore architecture and superior electrochemical performance, offering a scalable and sustainable route for next-generation supercapacitors. Recommendations for further enhancement include exploring alternative biomass precursors, dual-activation strategies, surface functionalization to maximize faradaic contributions, and integration into flexible or hybrid energy storage devices.

Project Overview

What This Project Is About

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The project explores creating porous carbon materials from natural or waste sources and testing them as energy storage components in supercapacitors. It combines simple processing steps to turn low-cost biomass into a porous structure that stores electric charge efficiently.

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The Problem It Addresses

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Many energy storage devices rely on expensive or non-renewable materials. Porous carbon from bio-sources offers a cheap, sustainable alternative, but achieving the right pore structure and conductivity for high performance is challenging. This project aims to make that process more accessible and scalable.

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Objectives of the Project

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1. Identify a suitable bio-source and prepare it for carbonization.
2. Develop a hydrothermal carbonization method to create initial porous structures.
3. Activate the carbon to enhance porosity and surface area.
4. Characterize the material’s structure, surface, and electrical properties.
5. Assemble a simple test supercapacitor and measure performance.

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What You Will Do Step by Step

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1. Literature review to understand current bio-derived carbons and methods.
2. Prepare biomass samples and conduct hydrothermal carbonization.
3. Apply activation (chemical or physical) to develop pores.
4. Use techniques like BET, SEM, and electrical tests to characterize.
5. Fabricate a small-scale supercapacitor and perform charge–discharge tests.
6. Analyze data to relate pore structure to performance.
7. Compare results with literature benchmarks and discuss limitations.
8. Suggest improvements and potential real-world applications.

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Expected Outcome

Anticipated porous carbon with good surface area and electrical conductivity, yielding stable, high-performance results in a simple supercapacitor setup. The project should demonstrate a link between biosource choice, activation method, pore structure, and energy storage efficiency, highlighting cost and sustainability benefits.