Sustainable Carbon Materials Derived from Biomass for Energy Storage Systems

The global demand for energy needs the development of new and efficient technologies capable of storing energy in many ways. Every sector within the energy field is undergoing innovations to meet market requests. Alongside optimizing energy storage devices and systems, extensive research is being conducted on materials that can enhance and improve the performance of energy systems. Carbon-based materials constitute a significant part of this market due to their exceptional conductive properties, tunable porosity, and morphological versatility, making them ideal candidates for energy-storage applications. In the idea of designing more sustainable devices while avoiding the depletion of fossil fuels, carbon-based materials can be derived from biomass resources. Biomass represents an abundant, cost-effective, and easily recoverable carbon source. Several carbonization methods can be employed depending on the desired final product. For solid carbon materials, the most common approaches are pyrolysis and hydrothermal carbonization, yielding distinct carbon materials tailored for specific applications. The use of activated carbon and hard carbon derived from biomass in energy applications offers significant advantages in terms of capacity, energy density, cost, and safety for emerging energy storage devices. In this thesis project, agricultural and cereal by-products were processed using two different synthesis methods to produce activated carbon and hard carbon. Activated carbons were obtained through pyrolysis combined with chemical activation using KOH at two different concentrations to evaluate surface area and porosity development. These materials were tested as electrodes in aqueous supercapacitors, aiming to minimize the use of toxic and environmentally unfriendly reagents in energy devices. Two electrolytes, one with alkaline pH and the other neutral, were employed. It was demonstrated that the combination of specific porosity characteristics with a neutral electrolyte extended the potential window of aqueous supercapacitors up to 1.7 V, instead of 1 V, reaching an energy density of 22.5 Wh·kg-1. Activated carbons were also investigated as solid hydrogen adsorbents, focusing on their ability to adsorb and release H2 under liquid N2 temperatures. This study evaluated the storage performance of different precursors and surface areas, providing a comprehensive understanding of potential materials for hydrogen storage applications. The best result in terms of gravimetric capacity was achieved by rice-derived activated carbon with a 6:1 activation of 4.8 wt%. Finally, hard carbons were tested as anodes in Na-ion half-cells with the aim of synthesizing carbons comparable to those currently available on the market. The synthesis involved hydrothermal carbonization followed by high-temperature annealing. To determine optimal parameters, three syntheses were conducted at different temperatures, allowing for the observation of physicochemical changes in the samples. Two biomass types, rice husk and corncob, were utilized in this study, with corncob-derived hard carbons demonstrating excellent performance in terms of capacity with a high coulombic efficiency of 89% and long cycle stability. In general, this study demonstrates the versatility of carbon-based materials derived from biomass for various energy storage applications, illustrating the potential of simple and scalable synthesis processes.