Insights into the Particle Hydrophilicity and Electrical Conductivity for the Construction of a Highly Efficient Electrical Percolation Network in Flow Electrode Capacitive Deionization

In flow electrode capacitive deionization (FCDI), a stably dispersed slurry with well-developed conductive networks is required to obtain a satisfactory desalination performance. In this work, slurries containing hybrid fillers with various dimensions, electrical conductivities, and surface characteristics were studied for FCDI desalination. The desalination performance was significantly influenced by the electrical conductivity and surface hydrophilicity of activated carbons (ACs). Even though hydrophobic ACs with high conductivity showed better adsorption capacity, a stable operation of FCDI was not possible due to the poor dispersion of the AC slurry, resulting in the risk of obstructing the flow channels of the FCDI cells. Combining the merits of the dispersion quality of hydrophilic AC and the electrical conductivity of multiwalled carbon nanotubes (MWCNTs), a mixed slurry containing AC and MWCNTs was developed. The MWCNTs served as conductive bridges between the AC particles, creating a strong electron conduction network. With the addition of 0.10 wt % MWCNTs, a 70% improvement in SAC from 6.51 to 11.05 mg/g was achieved because of the formation of a well-developed electrical percolation network.