An integrated strategy for long-term carbon sink and sustainable supercapacitor material production (Flexible Funding 2023)

Jiacheng Sun, University of Edinburgh, was awarded funding in the UKCCSRC’s Flexible Funding 2023 call to look at “An integrated strategy for long-term carbon sink and sustainable supercapacitor material production”.

The Microalgae Biochar Supercapacitor Material (MBSM) project was developed to tackle multiple global challenges, focusing on the production of sustainable materials, carbon capture and storage. In the MBSM project, biochar derived from lignocellulosic biomass and wastewater algae is optimized for use in supercapacitor applications, while simultaneously contributing to carbon sequestration and phosphorus recovery. The project’s sub-projects explore the activation techniques and feedstock choices to enhance the electrochemical properties of biochar.

The MBSM project focuses on producing biochar with specific properties that support energy storage while offering environmental benefits. The project is structured around two sub-projects, each addressing different aspects of biochar optimization: supercapacitor performance of lignocellulosic biochar and phosphorus recovery from algae biochar.

Figure 1 illustrates the flowchart of biochar produced from different feedstocks and activation processes. Lignocellulosic biochar, derived from straw and wood, showed varying degrees of specific capacitance based on the type of feedstock used and the activation method employed.

Figure 1. Lignocellulosic biochar based supercapacitor materials

The Role of Feedstock and Activation Process

The first sub-project, titled “The Role of Feedstock and Activation Process on Supercapacitor Performance of Lignocellulosic Biochar”, investigated the effects of different biomass feedstocks and activation methods on biochar’s electrochemical properties. This sub-project analyzed wood and straw feedstocks, and used CO2, steam and KOH activation to optimize biochar performance.

• Feedstock Performance: Straw-derived biochar was found to have higher specific capacitance than wood-derived biochar, despite the latter having greater electrical conductivity and porosity. This highlights the importance of feedstock selection in maximizing performance.
• Activation Trade-offs: Chemical activation using KOH produced biochar with higher surface areas and capacitance, but at the expense of electrical conductivity, indicating a balance needs to be struck between these properties.

This research provides valuable data on how different feedstocks and activation processes can be tailored to meet supercapacitor material requirements, which are essential for sustainable energy storage applications.

Phosphorus Recovery and Algae Biochar Performance

In the second sub-project, “Synergistic Valorisation of Wastewater Microalgae: Sulphuric Acid-Assisted Phosphorus Recovery and Enhanced Electrochemical Performance of Biochar for Supercapacitors”, the focus shifted to algae-derived biochar. Phosphorus recovery from wastewater algae was optimized using sulphuric acid, which also enhanced the biochar’s electrochemical properties (Figure 2).

• Phosphorus Recovery: Sulphuric acid leaching enabled phosphorus recovery rates of up to 95%, providing a solution for phosphorus pollution while promoting its reuse in agriculture, aligned with circular economy principles.
• Electrochemical Enhancement: The process improved the porosity of algae biochar and introduced sulfur-containing functional groups, increasing its specific capacitance to as high as 486.3 F g⁻¹, making it a promising candidate for supercapacitor electrodes.

Analysis of the phosphorus recovery process offers crucial insights into the dual benefits of algae biochar for both environmental remediation and energy storage.

Figure 2. Cyclic voltammetry curves of AN550 (Seaweed) and WM550 (Wastewater microalgae) derived biochar materials at scan rates of 10, 20, 40, 60, and 80 mV s−1.

Synergy Between Sub-Projects

Both sub-projects are integral to the overarching goals of the MBSM project, demonstrating the multifaceted applications of biochar in sustainability and technology.

• Sustainable Material Development: By exploring different biomass feedstocks, including lignocellulosic materials and wastewater algae, the project shows how biochar can be converted into high-performance supercapacitor materials, contributing to the transition to renewable energy.
• Carbon Sequestration: Biochar’s ability to lock carbon in stable forms supports the project’s carbon-negative approach. The results of both sub-projects emphasize the potential of biochar to reduce carbon emissions, whilst addressing the growing need for sustainable materials.
• Phosphorus Recovery: The algae biochar sub-project adds an environmental dimension by tackling phosphorus pollution and recovery. Phosphorus, a critical agricultural resource, is effectively reused, closing the loop in a circular economy model.

The quality of the biochar produced in the MBSM project is strongly dependent on the feedstock and activation methods used. Both sub-projects demonstrate the potential of biochar to serve as a sustainable material for supercapacitors, whilst contributing to environmental goals like carbon sequestration and phosphorus recovery. Although further research is needed to refine these methods for commercial applications, the MBSM project offers promising pathways for addressing pressing sustainability challenges.

Read more on Jiacheng’s Flexible Funding 2023 project page.