High energy density and long cycle life near-neutral Zn-air rechargeable batteries using polyoxometalates nanoclusters as homogenous catalysts

Even though Li-ion batteries have dominated the market so far, they lack the desired properties for large scale electric grids or electric vehicles. Besides, there are some concerns regarding the safety and raw-materials availability in the future. In this context, Zn-air batteries emerge as the most promising candidates to be the post-lithium technology for their lower weight and volume, and inherently safety. However, their cycle life is still below the required standards. Therefore, the goal of this proposal is to develop efficient electrically rechargeable Zn-air batteries with high energy density and cycling stability. To achieve this, near neutral electrolytes will be used instead of traditional highly alkaline solution employed in non-rechargeable devices. The latter leads to significant improvements in Zn anode cyclability increasing battery life. However, to fully exploit the potential of this technology, bifunctional catalytic materials specifically design to operate in this pH conditions are necessary and still missing. This project seeks to address this matter using metal oxide nanoclusters, known as polyoxometalates (POM), as homogenous bifunctional catalyst to promote both oxygen evolution and reduction reactions. These materials have outstanding electrochemical properties including an excellent reversibility, which makes them ideal for rechargeable energy storage devices. This research plan will investigate the electrocatalytic activity of various POMs in near neutral electrolytes using several electrochemical techniques. These will be later test in lab-scale Zn-air batteries to assess the performance of POMs as bifunctional catalyst in real operating conditions. The combination of near-neutral electrolytes and POM-based air cathodes is expected to allow fabrication of ZAB devices with increased cycle life, specific and volumetric energy density and power density. These improvements will consolidate ZAB secondary batteries as a post-lithium technology