Nanocarbons and Mediators for Energy Storage

Abstract

Renewable energy sources are important for switching from harmful energy systems to eco-friendly options because of environmental problems caused by industrialization and the growing demand for fossil fuels. Energy Storage Systems (ESS) are crucial for the development of renewable energy sources, which are inconsistent and depend on time and weather. The growth of electric vehicles also requires new ESS that can store and provide high energy and power. Electrochemical energy storage is especially important for this transition._x000D_ _x000D_ This thesis focuses on the enhancement of ESS through the addition of nanocarbons and multiredox nanosized oxides as dispersed conducting agents in zinc-air batteries and vanadium redox flow batteries (VRFBs). Nanocarbons are expected to increase the total active surface area, improve electrical conductivity, and build percolation networks for electrons. Multiredox nanosized oxides, such as polyoxometalate clusters and iridium oxohydroxide, act as redox mediators and catalysts for the oxygen reactions, enhancing the efficiency and reversibility of the battery cycling._x000D_ Various characterization techniques to understand the structure, composition, and electrochemical properties of the nanomaterials have been employed within the thesis. Electrochemical measurements are conducted to evaluate the performance of the modified electrolytes and anodes in VRFBs and zinc-air batteries._x000D_ For Zn-air batteries, the research highlights the significant enhancements in current densities and reductions in overpotentials for oxygen redox reactions achieved by incorporating nanocarbons as dispersed conducting agents and redox particles as mediators. The discovery of a bipolar effect on the conducting particles facilitated additional charge transfer mechanisms, leading to superior electrochemical performance. Although initial attempts to use a single electrolyte for both Zn and O2 half-cells were unsuccessful due to pH incompatibilities and Zn passivation, the use of carbon-based suspensions showed promise in improving cycling stability through protective coatings on Zn anodes._x000D_ In the domain of VRFB, the incorporation of Super P nanoparticles was found to form percolation networks that decreased charge transfer resistance and overpotentials while increasing current density. The complete redox flow cell study underscored the necessity of optimizing cell geometry to prevent clogging and improve electrolyte flow, highlighting the potential of small amounts of carbon black as a cost-effective alternative to traditional high-cost collectors._x000D_ _x000D_ The results are expected to contribute to the development of more efficient and sustainable energy storage systems, enhancing the transition to renewable energy sources and reducing environmental impacts.

Date of Award	2 Dec 2024
Original language	English
Supervisor	Dino Tonti (Director) & Maria Nieves Casañ Pastor (Director)