• Energy Research

AbstractAn eco‐friendly and sustainable salt‐templating approach was proposed for the production of anode materials with a 3D sponge‐like structure for sodium‐ion capacitors using gluconic acid as carbon precursor and sodium carbonate as water‐removable template. The optimized carbon material combined porous thin walls that provided short diffusional paths, a highly disordered microstructure with dilated interlayer spacing, and a large oxygen content, all of which facilitated Na ion transport and provided plenty of active sites for Na adsorption. This material provided a capacity of 314 mAh g−1 at 0.1 A g−1 and 130 mAh g−1 at 10 A g−1. When combined with a 3D highly porous carbon cathode (SBET ≈2300 m2 g−1) synthesized from the same precursor, the Na‐ion capacitor showed high specific energy/power, that is 110 Wh kg−1 at low power and still 71 Wh kg−1 at approximately 26 kW kg−1, and a good capacity retention of 70 % over 10000 cycles.

Faradaic deionization (FDI) is an emerging and promising electrochemical technology for stable and efficient water desalination. Battery-type energy storage materials applied in FDI have demonstrated to achieve higher salt removal capacities than carbon-based conventional capacitive deionization (CDI) systems. However, most of the reported FDI systems are based on inorganic intercalation compounds that lack cost, safety and sustainability benefits, thereby curtailing the development of a feasible FDI cell. In this work, we introduce an all-polymer rocking chair practical FDI cell, with a symmetric system composed by a redox-active naphthalene-polyimide (named as PNDIE) buckypaper organic electrodes. First, electrochemical performance of PNDIE in 0.05 M NaCl under open-air conditions is evaluated in both three-electrode half- and symmetric FDI full-cell using typical lab-scale electrode dimensions (1.6 mgPNDIE; 0.78 cm2), revealing promising specific capacity (115 mAh g-1) and excellent cycle stability for full-cell experiments (77 % capacity retention over 1000 cycles). Then, all-polymer rocking chair FDI flow cell was constructed with practical PNDIE electrodes (92.2 mgPNDIE; 9.6 cm2) that delivered large desalination capacity (155.4 mg g-1 at 0.01 A g-1) and high salt removal rate and productivity (3.42 mg g-1 min-1 at 0.04 A g-1 and 62 L h-1 m-2, respectively). In addition, long-term stability (23 days) experiments revealed salt adsorption capacity (SAC) retention values over 95% after 100 cycles. The overall electrochemical and deionization performances of the reported technology is far superior than the state-of-the-art CDI and FDI techniques, making it a competitive choice for robust and sustainable “water-energy” electrochemical applications. NP appreciates fellowship IJC2020-043076-I-I funded by MCIN/AEI/0.13039/501100011033 and by the European Union NextGenerationEU/PRTR. NP and RM acknowledge PID2021-124974OB-C21 financed by MCIN/AEI/10.13039/501100011033/FEDER "A way of making Europe". NG acknowledges the funding from the European Union’s Horizon 2020 framework programme under the Marie Skłodowska-Curie agreement No. 101028682. AFP and JJL appreciates the Talento’s program of the Community of Madrid which involves the project SELECTVALUE (2020-T1/AMB-19799). The authors also would like to thank Gonzalo Castro and Ignacio Almonacid for collaborating in the laboratory experiments and the sample analysis.