Water Desalination By Capacitive Deionization Using Electrospun Micro-Mesoporous Ultrafine Carbon Fibres
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Date
2024-08
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NM-AIST
Abstract
Capacitive deionization is a promising method for desalination of low-to-moderate salinity water. Electrode pore structure is an important factor influencing performance in this technology. For the majority of carbon materials including ultrafine carbon fibres used as electrodes for capacitive deionization, excessive microporosity has hampered optimal performance. In this study, mesoporous ultrafine carbon fibres (277–700 nm diameters) were fabricated from polyacrylonitrile blended with cellulose acetate or terephthalic acid through electrospinning and carbonization for use as capacitive deionization electrodes. Fibre surface and pore attributes were adjusted by varying the proportions of the blended polymers while ensuring no adverse change in their tangible attributes. Fibre structure was further modified by
embedding or hydrothermally coating MoS2 nanoparticles to enhance desalination performance through faradaic means. The produced blend-based fibres attained a specific surface area of 925.47 m2/g and a pore volume of 0.7884 cm3/g. Electrochemical tests revealed increasing specific capacitance and reducing charge transfer resistance with increase in surface area and mesopore volume. For MoS2-loaded fibres, hydrothermally-grown MoS2 yielded enhanced charge transfer and higher diffusion-controlled capacitance than the embedded MoS2. Desalination performance was evaluated under various configurations including conventional setup, single and multi-channel asymmetric cells, and multi-channel battery deionization setups. A specific adsorption capacity of 8.03 mg/g was achieved in the plainltrafine carbon fibres using 20 mM NaCl in batch mode at 1.2 V. The highest specific
adsorption capacity attained was 32.11 mg/g using 20 mM NaCl in a four-channel battery deionization cell at ±0.8 V. In energy utilization, the MoS2-coated ultrafine carbon fibres when used in a battery deionization cell demonstrated over 3.7 times higher thermodynamic energy efficiency than in the asymmetric setups and 50 times higher than in conventional setups, while
maintaining consistent desalination performance. The electrodes in the battery deionizationcells benefited from the coupled effects of electrosorption/intercalation and ion exchange membranes in symmetric conformation to effectively utilize charge. These findings promote the use of cellulose acetate and terephthalic acid as excellent pore templates in mesoporous ultrafine carbon fibre fabrication for capacitive deionization and provide insight into process engineering for improved electrochemical desalination and enhancement in ion intercalation based desalination configurations.
Sustainable Development Goals
SDG - 6: Clean Water and Sanitation
SDG - 7: Affordable and Clean Energy
SDG - 9: Industry, Innovation, and Infrastructure
SDG - 12: Responsible Consumption and Production