Capacitive deionization (CDI) is a developing water desalination technology in which a potential applied across two carbon-based electrodes electrostatically attracts ions out of solution. The limitations of CDI revolve around charge efficiency (i.e. how many ions are removed per electrical charge applied) which is mostly governed by the physical design and structure of the electrodes. We explored the use of chitosan, a biodegradable polysaccharide, as an electrode binder and compared it to the standard petrochemically-derived polyvinylidene fluoride (PVDF) binder used in most supercapacitors and CDI systems. Preliminary data shows electrodes with a chitosan binder are capable of removing up to twice as much salt per gram of electrode with improvements in charge efficiency of 20-100% compared to electrodes with PVDF binders. We hypothesize the improved performance stems from the increased hydrophilicity which allows for greater electrode pore access, and the introduction of ambient surface charge which reduces parasitic co-ion expulsion. As the degree of protonation of chitosan’s amine group is pH dependent (pKa ≈ 6.5), desalination tests at varying pH demonstrated improved charge efficiency with decreasing pH, reinforcing the notion that ambient charge improves performance. While being comparable in price, chitosan dissolves in weak acidic solutions whereas PVDF requires expensive and dangerous organic solvents, giving chitosan the potential to be an economical and sustainable replacement for PVDF binders in CDI systems.

Enhanced capacitive deionization performance using electrodes with polysaccharide binders

252nd National Meeting (2016)

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