Membrane Capacitive Deionization with Barley Straw Biochar-Based Electrodes for Hardness Control

Recently, there have been increasing challenges in handling surplus biomass such as barley straw, and technologies that utilize these materials to create high value-added resources, such as electrode materials, are gaining considerable attention. In this study, a barley straw biochar-based activated carbon was synthesized from an agricultural by-product and evaluated for membrane capacitive deionization (MCDI). The electrochemical properties and hardness removal performance of the fabricated electrode were systematically investigated and compared with those of six commercial activated carbon electrodes. The biochar-based electrode exhibited a morphology comparable to commercial electrodes and showed typical electric double-layer capacitive behavior. The MCDI system achieved a deionization capacity of approximately 14 mg/g and a deionization rate of 0.035 mg/g/s. Although the deionization rate was slightly lower than that of some commercial electrodes, the biochar-based electrode demonstrated comparable deionization capacity and energy consumption (approximately 0.98 Wh/g-CaCl2). In addition, excellent cycling stability was observed, with 94.6% of the initial charge capacity retained after 180 cycles and Coulombic efficiency exceeding 99%. These results demonstrate that barley straw biochar-based activated carbon is an alternative to commercial activated carbon electrodes for CDI-based hardness control.