Polyelectrolyte-coated zeolite-templated carbon electrodes for capacitive deionization and energy generation by salinity exchange

• Soft ZTC is a promising electrode material for both CDI and CapMix techniques. • Polyelectrolyte-coated ZTC enhances CDI: high salt adsorption with low energy cost. • Soft ZTC electrodes are used for the first time in energy generation by salinity exchange. • Soft ZTC electrodes with IEMs minimize leakages and maximize energy harvesting in CapMix. As global demands for freshwater and renewable energy intensify, capacitive deionization (CDI) emerges as a promising technique for water purification, desalination, and ionic separation. Reciprocally, energy harvesting has been made possible from exchanging solutions with different salinity, using the so-called capacitive mixing (CapMix) methods, now taking their first steps towards a wider range of application. In all the techniques mentioned, porous electrodes are used in order to maximize the stored charge, making it essential to properly select the material of which the electrode is composed. This work focuses on exploring the performance of zeolite-templated carbon (ZTC) as a highly promising electrode material. ZTC offers ordered pore distribution and high electrical conductivity, making it in principle ideal for energy harvesting and water purification applications. In order to optimize its performance, the surface of the ZTC is for the first time modified by application of polyelectrolyte coatings, resulting in so-called soft electrodes or SEs. This combination of electrode material and functionalization gives rise to a highly efficient and low energy-consuming strategy to fully realize the potential of this carbon material in CDI and CapMix techniques for tackling global freshwater and energy challenges. Energy and power generation values up to 25 mJ and 7.5 mW m −2 have been obtained (with measured potential rises of 131 mV by only exchanging salinities of the bathing solution), which overcome values such as 4.3 mW m −2 previously found in our laboratory under similar conditions.