Estudio del óxido de bismuto, y otros óxidos metálicos, como electrodos positivos en baterías de zinc

Abstract

This doctoral dissertation has been presented in the form of thesis by publication. Today, rechargeable batteries are at the spotlight of numerous research groups, since they are one of the fundamental topics in the search for alternative, sustainable, economical and reliable energy sources. Currently, lithium-ion batteries are the most marketed and ever-present batteries in a multitude of portable electronic devices (smartphones, laptops, tablets, etc.) and hybrid and electric vehicles (cars, motorcycles, scooters, bicycles, etc.). etc.). However, these batteries do not quite meet expectations in terms of energy requirements. This, together with the associated security problems, means that its use does not fulfil the requirements needed in fundamental services. There of arises the need to find an alternative type of battery with good energy density, an affordable price and good safety This is zinc-based batteries (zinc batteries with different metal oxides or zinc-air batteries) become important, since they emerge as a real alternative to the batteries currently marketed. Bismuth oxide (Bi2O3 exhibits some very interesting properties, such as its high practical capacity, which closely approaches the theoretical capacity. Its exceptional redox reversibility results in a remarkable cyclability and high discharge capacity. However, the use of bismuth oxide has long been limited to be a mere additive in anodes to suppress hydrogen evolution. In this study, electrodes composed of t Bi2O3 as active material have been investigated, using them in zinc batteries with different electrolytes through spectrochemical and electrochemical tests. Thus, a research line has been established in which Bi2O3 is employed as the main material in rechargeable zinc batteries. To achieve versatile and safe rechargeable batteries, polymeric gel electrolytes (GPEs) play a crucial role, as they are responsible for replacing liquid electrolytes to prevent potential leaks and safety issues during battery operation. In this study, GPEs primarily based on PVA doped with KOH have been used in batteries. It has been confirmed that these gels work perfectly when employed in different types of batteries, yielding excellent results in terms of conductivity and cyclability. This highlights the durability of this material and its practical application in electrochemical devices. When designing a battery, the long-term behavior must be considered. This is usually accomplished by cycling it for a period, but it is unknown what happens inside when it fails. To monitor batteries while cycling, information from the electrodes must be obtained separately. This was accomplished with very good results by monitoring both electrodes separately during operation, thanks to the incorporation of a pseudo-reference electrode. This method, extremely helpful in our work, enable researcher, general speaking for faster and more efficient progress in research. In this work, materials based on RuO2 obtained from the thermal decomposition of precursors have been used. These materials have demonstrated catalytic activities in both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). They have been tested as catalysts in Zn-Air batteries, achieving very promising results.