Feeding long-term sustainability to our planet is becoming a major must, given the urgent need to preserve our natural resources, reduce pollution and protect the natural ecosystems. Sustainable development holds on three pillars, namely environmental sustainability and protection, economic viability, and social equity. Among them, the former receives great attention and it is build up on reducing carbon emissions and footprint, packaging waste, water usage, and other negative environmental impacts. New paradigm towards green chemistry, sustainability, and circular economy in the chemical sciences must be developed, in order to better employ, reuse, and recycle the materials employed in every aspect of modern life. Following this approach, electrochemical reactions have found technological applications in various fields, including electrochemical synthesis, energy storage, and environmental remediation [1]. Sustainability and electrochemistry are therefore closely related. In this talk, the utilization of electrochemical tools together with bio-based or sustainable materials is presented.

First, the exploration of new synthetic routes to reduce the toxicity of residual monomer and other chemicals employed (initiators, surfactants) during the fabrication of polymer hydrogels, one of the most promising groups of biomaterials, is required. With a similar approach to the previously developed "green" and clean production of polymer nanogels, largely used in biomedicine, based on the recourse to high energy irradiation, electrochemical advanced oxidation technologies were used to crosslink hydrogels of poly(vinylpyrrolidone)(PVP) by means of electrogenerated hydroxyl radicals. This facile electrosynthesis route showed that the kind of radicals strongly drives the transformation of the architecture of linear, inert polymer chains into a functionalized nanogel (with -COOH and succinimide groups), more suitable for further conjugation [2-4].

Second, the conversion of bio-based polymers such as chitosan and agarose, into eco-friendly carbonaceous electrodes is described, as a suitable choice for promoting sustainability due to their low cost and high activity/selectivity [5-6]. The use of mesoporous carbon supports both reduce the amount of noble metals employed as electrocatalysts and enhance the accessibility of reactants to the active sites. On the one hand, excellent electrocatalytic performance of N-doped chitosan-derived carbons and large surface area agarose-derived carbons are responsible of the high efficiencies achieved (above 95%), allowing the fast destruction of pharmaceutical residues in electro-Fenton treatment. On the other hand, chitosan-derived mesoporous carbons served as optimal supports for PtCu electrocatalysts, evidencing an increased activity of both the four-electron ORR and the methanol oxidation reaction as compared to commercial supported Pt and PtCu catalysts, which is attributed to the good balance achieved between micro/mesoporosity.

Finally, one of the most appealing and recent trends in the application of biopolymers in electrochemical water treatment is reported. The co-generation of freshwater and sustainable energy in a closed loop where the solar energy is used not only for water purification treatment with porous materials like hydrogels, but also for thermoelectric power generation, by means of material transpiration and diffusion processes. The photothermal electricity production is promoted by hydrogels based on biopolymers such as alginate (ALG) and thermosensistive materials like poly(N-isopropylacrylamide) (PNIPAAm). ALG-PNIPAAm bio-hydrogel, modified with conducting polymer (CP), as thermal absorber component, was used to obtain freshwater from seawater desalination under sunlight. Higher evaporation rates (> 4 kg/h*m²) have been observed in the presence of lineal CP, if compared with nanoparticles of CP [7-8]. Impedance measurements elucidate the ion diffusion dynamics within the hydrogel, directly correlating this behavior to enhanced power generation; these results revealed that the presence of hydrophilic groups (─OH, ─SO₃H), present in the CP backbone, promotes the capillary flow of the electrolyte during the sunlight irradiation. The doped CP molecules facilitate a fast ion transport thanks to a good balance between the material hydrophilicity and the interconnected pores.