Enhancing Electrode Efficiency in Capacitive Deionization with Surface-Modified Biochar

This study delves into the innovative use of surface-modified biochar as a dynamic electrode material for the removal of chloride and fluoride ions through capacitive deionization. By incorporating titanium dioxide and amine groups into the biochar structure, the modifications aim to augment surface-active sites which enhance ion diffusion, boost charge efficiency, and elevate cation/anion selectivity in asymmetric capacitive deionization configurations.

Titanium dioxide-enhanced biochar, amine-functionalized biochar, and activated biochar are referred to within the study as TB, AmB, and AcB, respectively. Comprehensive physical and electrochemical characterizations shed light on the altered surface properties of these materials. Notably, at an optimal titanium dioxide loading of 5% (denoted as TB-05), the specific capacitance of the TB-05 electrode increased by 35% at a scan rate of 1 mV s^(-1), compared to the AcB electrode. This enhancement came despite a reduction in specific surface area.

The efficacy of various capacitive deionization cell designs was also tested, including three asymmetric (AmB||TB-05, AcB||TB-05, and AmB||AcB) and two symmetric (AcB||AcB and TB-05||TB-05) configurations. Among these, the symmetric TB-05||TB-05 setup exhibited a significant 42% improvement in NaCl removal capacity at 8.51 mg g^(-1) over the symmetric AcB configuration, which achieved 6.01 mg g^(-1). The asymmetric AmB||TB-05 cell design further highlighted a 67% increase in charge efficiency compared to the symmetric AcB cell, likely attributed to a mitigated co-ion effect. In fluoride ion removal applications, the symmetric TB-05 cell demonstrated a capacity of 3.51 mg g^(-1).

The implications of this research are profound, promoting simple yet effective surface-modification techniques to transform inexpensive commercial biochar into a sustainable and efficient electrode material. This paves the way for the broader application of biochar in scalable asymmetric capacitive deionization technologies, potentially revolutionizing water purification methods.