A B S T R A C T N-doped carbon aerogels were synthesized by the polycondensation of resorcinolformaldehyde-melamine mixtures. The prepolymerization of the precursors was determinant for the preparation of meso/macroporous aerogels with varied nitrogen content, regardless the solution pH and M/R molar ratio. The effect was more pronounced at pH 6, as the hydrogels prepared by the one-step route displayed essentially a microporous character, as opposed to the mesoporous network after prepolymerization. The prepolymerized carbon aerogels presented large capacitance values due to the optimum balance between pore structure, improved wettability and low polarization resistance for the highly doped materials. Salt deionization capacity revealed the importance of the macropore structure in the monolithic configuration of the aerogels for a fast electrosorption of ions.

A simple modification of the conventional sol-gel polymerization of resorcinol-formaldehyde mixtures allowed a facile preparation of ultrahigh mesoporous carbon gels. In the conventional synthesis the growth of the cluster polymer particles leading to the development of the porosity is controlled by the R/C ratio. In the presence of a carbon conductive additive, the polymerization of the reactants proceeded through the formation of less-branched polymer clusters resulting in carbon gels with large pore volumes within the micro/mesoporous range. The obtained materials displayed unusual heterogeneous pore systems characterized by large mesopores interconnected by necks of variable sizes, along with an enhanced electrical conductivity provided by the carbon black additive. The gels showed stable electrochemical response in neutral aqueous electrolyte, being reversibly charged/discharged at large potential windows, without significant losses in the current density, chemical modifications or structural collapse. The enhanced life cycle of these electrodes makes them good candidates for their use in electrochemical applications where a fast response and high cycleability is required.

A porous carbon gel obtained from the poly-condensation of resorcinol and formaldehyde was synthesized and used as an electrode material for the capacitive deionization (CDI) of synthetic brackish water. The desalting capacity of this material was evaluated in terms of applied voltage and zero-voltage regeneration over a number of cycles, and compared to that of commercially available carbon materials (powdered activated carbon and activated carbon cloth). Due to an adequate combination of chemical and porous features, the deionization capacity of the carbon gel electrode exceeded that of the electrodes based on conventional microporous carbons over a larger number of adsorption/regeneration cycles. An almost fully reversible ionic removal (ca. 90 % recovery) was obtained for this electrode material when regeneration was carried out at zero-voltage conditions. Characterization of the cycled electrodes showed that the carbon gel was resistant to electrochemical anodic oxidation under the polarization conditions used (applied voltage of up to 1.2 V), whereas the electrodes produced from the two commercial carbon materials undergo severe modifications (oxidation and a decrease in surface area) when the applied voltage was maintained for several cycles.

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Four carbon aerogels with varied micro/mesoporous texture were synthesized and their electrochemical response for the electro-adsorption of ions investigated in saline electrolyte. As a general trend, the ability of the electrodes to electrosorb ions depended on the microporosity, whereas the large pores (mesopores) had a strong influence on the kinetics of the electrosorption process. The aerogels exhibiting a well developed microporosity interconnected by a large mesoporous network showed large capacitance values and fast electro-adsorption kinetics. Indeed, the diffusion of the ionic species in solution controls the performance of the electrodes at high current loadings (or scan rates). Optimized electrode materials should combine pores within the micropore range to effectively electrosorb ions and large mesopore volumes for a fast diffusion of the ionic species in solution. An adequate meso/micropore ratio in the mesoporous carbon aerogels here reported allowed to record a capacitance value of 75.8 F g-1 .