Graphite felt 3D framework composites as an easy to scale capacitive deionization electrode for brackish water desalination

Abstract

Capacitive Deionization (CDI) is an emerging technology for brackish water desalination. Currently, CDI technology lacks practical means of scaling electrodes from the laboratory to pilot plant level for pre-commercial applications. With the aim of solving the scalability issues, we have prepared easy to scale 3D composites using the highly conductive macrostructure of a graphite felt (GF) as electron transfer channel with the microstructure of activated carbon (AC) to furnish ionic adsorption sites (GF-AC). The electrochemical characterization of GF-AC (1 cm2) showed a larger total ion storage capacity (25 F g−1, 40 mg cm−2, 0.79 F) as compared to an AC film electrode (93 F g−1, 1.5 mg cm−2, 0.11 F) prepared with the same active material. Moreover, a specific capacitance retention of 90% even after 5000 cycles was achieved showing a viable stability. GF-AC was then tested in a 1-Cell CDI System (10 cm2) reaching salt adsorption capacity (SAC) values of 5.2–8.7 mg g−1 and 57–67% in charge efficiency. Subsequently, long-term operation resulted only in a 30% SAC capacity loss after 120 cycles. Additionally, a strategy based on switching the electrode polarity was effectively used to recover CDI performance reaching 180 cycles with a 70% SAC capacity retention. Finally, the system was scaled to a 9-Cell Stack (300 cm2) demonstrating excellent performance (8.7 mg g−1 SAC, 2.6gSALT m−2 h−1 and 63% charge efficiency). Furthermore, the CDI system showed that brackish water desalination (from 2.1 g L−1 to 1.5 g L−1; WR = 50%) could be performed at 2.26 L m−2 h−1 and 0.60 kWh m−3. Therefore, we believe that GF-AC electrodes hold great promise for large-scale CDI practical applications.