Strategies to boost capacitive deionization performance of 3D electrodes

[Display omitted] •Strategies to improve CDI performance of 3D graphite felt composite electrodes were studied.•A boost of salt adsorption capacity and salt adsorption rate up to 200% can be achieved by using thinner electrodes.•Increasing the mass loading from 31.7 to 55.5 mgACcm−2 improved salt concentration reduction in 57%.•Graphite felt with high dispersed AC led to an improvement of 45% in salt adsorption rate and 59% in productivity.•Combination of suitable thickness, AC mass loading and distribution is critical. Graphite Felt (GF) 3D composite electrodes are promising candidates for emerging electrochemical water treatments such as capacitive deionization (CDI). In the present work, simple strategies to improve their performance based on modifying electrode thickness, activated carbon (AC) mass loading, and its distribution over GF were explored. Electrochemical characterizations showed that by reducing electrode thickness and increasing mass loading, increments of 45% in the case of total capacitance (F) and 70% in terms of specific capacitance (FgAC−1) could be achieved. CDI experiments demonstrate that values of salt adsorption capacity (SAC) and concentration reduction (Δc) can be improved by more than 200% when reducing GF electrode thickness from 6.0 mm to 2.6 mm. Additionally, by using the thinnest electrodes and increasing AC mass loading, values of Δc over 50% higher were reached in accordance with the electrochemical analysis. However, this achievement was obtained penalizing SAC, ASAR, productivity (P) and, energy consumption (EV) mainly due to the larger occurrence of Faradaic reactions. Moreover, microscopy images showed that the AC was not uniformly distributed over the GF structure, just on the outer surface, impairing the penetration of electrolyte inside the electrodes. Further research, focused on adjusting the synthesis conditions, enabled us to prepare electrodes with a more homogeneous dispersion of AC. These highly distributed GF composites produced a significant enhancement in terms of ASAR (45%) and P (59%). This progress on optimizing the preparation of GF composite materials by using simple strategies has paved the way for improving the electrochemical separation of ions.