Carbon electrodes for capacitive deionization (CDI) are usually ranked by capacitance measured under conditions different from those of desalination. Six electrodes—a microporous activated carbon from waste coffee grounds, a micro-mesoporous templated carbon from magnesium citrate, their 1:1 mixture, and each with 5 wt% polyaniline (PANI)—were characterized electrochemically in 1 M H₂SO₄ and in the NaCl feed at the CDI cell voltage, and tested in batch-mode CDI at +1.6 V. For the three pristine electrodes, capacitance ranked the initial salt adsorption capacity (SAC) correctly in both electrolytes and by every technique, and their 1:1 mixture showed no synergy under the conditions tested. PANI raised the capacitance by 16–18% in acid, but in the feed its contribution varied between the carbons, was partly irreversible and did not follow the SAC, which fell for the coffee-waste carbon and rose for the templated one. No electrochemical measurement anticipated durability: all electrodes retained 95–100% of their capacitance over 10,000 cycles in acid, whereas the pristine ones lost most of their SAC within 100 CDI cycles, and PANI raised the mean SAC retention of the templated carbon from 12% to 76%. Capacitance is thus a useful first screen for purely capacitive carbons, but not for electrodes with a pseudocapacitive component or for predicting service life.

Porous carbon was prepared by direct carbonization of tri-lithium citrate tetrahydrate at 800 °C, followed by acid leaching and re-annealing. Pyrolysis produced Li₂CO₃ and Li₂O within the carbonizate; their removal left an oxygen-functionalized disordered carbon with an openwork structure of crumpled sheets, a BET area of 342 m² g⁻¹ and micropores near 0.9 nm that supply about 40% of the NLDFT surface area. In a symmetric cell with 6 mol L⁻¹ KOH, the carbon delivered a single-electrode capacitance of 91.5 F g⁻¹ at 0.5 A g⁻¹ and retained 80.2 F g⁻¹ at 5 A g⁻¹, with nearly rectangular voltammograms and coulombic efficiencies of at least 98.9%. In concentrated aqueous lithium bis(trifluoromethanesulfonyl)imide (10 mol kg⁻¹), three symmetric coin cells extended the voltage window to 2.0 V and gave a reproducible capacitance of 57.6 ± 0.2 F g⁻¹ at 0.2 A g⁻¹. In batch capacitive deionization with 10 mmol L⁻¹ NaCl at 1.2 V, the electrodes returned a stable charge of 1.4–1.5 C per cycle over 100 cycles and removed 2.54 ± 0.28 mg g⁻¹ of salt in the first five cycles; the decline in salt adsorption on cycling identifies charge efficiency as the next property to improve.