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Understanding and Optimising Carbon Disorder for High-Performance Supercapacitors https://doi.org/10.17863/CAM.121585 Liu, Xinyu 0000000263523517 Forse, Alexander Grey, Clare Addressing the growing need for sustainable energy storage solutions, electrochemical double layer capacitors (EDLCs) offer an attractive combination of rapid charge-discharge capabilities with moderate energy density and exceptiona durability. Nanoporous carbons, especially activated carbons, are the cheapest and most widely used electrode materials in commercial EDLCs. However, their structural complexity has made it challenging to determine the key structural factors that determine capacitive performance, leading to a lack of clear design principles for making nanoporous carbons with enhanced performance. This work investigates the structure-property relationship in amorphous nanoporous carbons to optimise electrode design for enhanced EDLC performance. The measurements on a series of 20 nanoporous carbon samples demonstrate no correlation between capacitance in 1 M TEABF4 (ACN) and average pore size, BET surface area or surface functionalities. These carbons exhibited a wide range of capacitance values (83-137 F/g), despite similar porosity characteristics. Instead, solid-state NMR spectra of electrolyte-soaked carbons show distinguished line shapes among carbons, with the chemical shifts of the in-pore resonances reflecting their distinct local structures. Further analysis of NMR spectra combined with simulations reveals a strong correlation between local order degree and capacitance. More disordered carbons with smaller graphene-like domain sizes exhibit higher capacitances. Raman spectroscopy, a conventional probe of local structural disorder in nanoporous carbons, is used to test the disorder-driven capacitance theory. Nanoporous carbons with lower ID/IG ratios and broader D bands, which indicate smaller graphene-like domains, have higher capacitance, aligning with NMR observations. The correlation between capacitance and ID/IG ratios demonstrates high consistency with the correlation observed between NMR-derived ordered areas. This provides a more accessible and rapid screening method compared to NMR, while Raman measures the level of disorder, it does not provide information on the ion adsorption capacity of the carbons. Low-temperature synthesis proves to be a promising pathway for making nanoporous carbons with smaller graphene-like domains with enhanced capacitance. HTC-600, the most disordered synthesised carbon, exhibited superior gravimetric (173 F/g) and volumetric capacitance (78 F/cm3), representing an improvement of ~25% over the best commercial activated carbons tested. With an expanded series of carbons, the ion adsorption capacity in the absence of applied potential, a parameter measured by NMR experiments, shows a strong correlation with capacitance. Nanoporous carbons with smaller graphene-like domains and higher ion adsorption capacity generally show enhanced capacitance. Combining graphene-like domain sizes and the ion adsorption capacity, it is evidenced that the capacitance of predominantly microporous carbons can be directly predicted from the NMR spectra of electrolyte-soaked carbons. The disorder-driven capacitance is tested in an ionic liquid electrolyte without solvent (EMIBF4). Nanoporous carbons with smaller graphene-like domains consistently show higher capacitance, regardless of the cation-anion combination, provided the ions can access the pores. This generality suggests that disorder-enhanced capacitance is an intrinsic property of carbon electrodes rather than an electrolyte-specific effect. Finally, ex-situ NMR experiments on two charged carbon electrodes with distinct capacitance suggest that the capacitance difference is related to the charge storage efficiency rather than the charge compensation mechanism. More disordered carbons have higher capacitance due to the more efficient storage of ions in their nanopores. Overall, this work establishes structural disorder as a key structural factor determining capacitance in nanoporous carbons, providing clear design principles for improving next-generation EDLC electrodes. These findings offer guiding principles for synthesising, fast screening and potentially enable machine learning approaches for automating the discovery of improved electrodes, thereby contributing to the enhancement of EDLCs and accelerating the transition to sustainable energy systems. University of Cambridge 2025-04-22 Thesis Doctoral Doctor of Philosophy (PhD) eng https://www.repository.cam.ac.uk/handle/1810/389804 embargo 2026-09-23 https://www.repository.cam.ac.uk/bitstreams/aae544eb-38f5-467b-9d3a-a41cf259d9e9/download e500b1d979fd2750d927901d24ca8421 https://www.repository.cam.ac.uk/bitstreams/3526149a-17c0-4fb2-bb28-3102c00ab107/download 87eda9de84448d1f82354d60eee3eb5f http://purl.org/NET/rdflicense/allrightsreserved Energy Storage EDLC Porous Carbon NMR Spectroscopy