Development of advanced electrolytes and electrocatalysts for electrochemical energy storage and conversion devices

Abstract

Development of flexible, scalable and portable electrochemical energy storage (EES) technologies is crucial to achieve a stable energy supply in various scenarios, and the innovation in the advanced materials for sustainable and efficient energy harvesting, conversion, storage, and utilization has been recognized as the key points. This thesis focuses on the design, synthesis, characterization and application of novel active materials for selected EES devices. The related background, operating principle, current progress, and existing challenges are comprehensively discussed. The first project presents research work on non-aqueous redox flow batteries (NRFBs), which is considered as the most promising EES technology for the modular, large-scale electrical grid. A novel electrolyte based on (nBu4N)4[MV13O33Cl] (M= V=O2+ {V14} or MgOH+ {MgV13}) {MV13}) in acetonitrile was explored for application as charge carrier for nonaqueous electrochemical energy storage. This project describes initial investigations into the electrochemical properties of the mixed-valent {MV13} cluster, revealing the viability of this compound to serve as multi-electron charge carrier in symmetric NRFBs. Benefiting from its excellent physicochemical properties (high solubility, stability and nano-size), the proposed NRFBs based on {MV13} cluster demonstrated remarkable battery performance. The second part investigates the safe, environmentally friendly zinc-air batteries (ZABs), which have high energy density, low-cost manufacturing and feasibility of scaling up. The sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) pose great challenges for ZABs in practical application. Thus, developing efficient and economic bifunctional ORR/OER electrocatalysts for rechargeable ZABs is urgently required. In this regard, atomically dispersed FeNi dual-metal pairs on the nitrogen-doped carbon matrix with a hierarchical structure wrapped by multi-walled carbon nanotubes is reported in this section. X-ray absorption spectroscopy and transmission electron microscopy were utilized to identify the FeNi dual atomic active sites. The electrochemical properties as well as rechargeable ZABs performance of this catalyst were systematically evaluated. Furthermore, a novel ultrathin Pd metallene doped with atomic WOx/MoOx ORR catalyst was also synthesized and characterized, demonstrating how defects engineering can be used to enhance electrocatalytic activity of the electrocatalysts. The electrochemical properties and practical performance of this catalyst in both primary and rechargeable ZABs were investigated in detail. The third part explores the development of electrocatalysts for trifunctional zinc-nitrate/nitrite batteries (ZNBs), which can achieve sustainable energy supply, electrosynthesis of green ammonia and degradation of the NO3-/NO2- pollutant in wastewater simultaneously. Compared with traditional Haber-Bosch plants, this ZNBs device features fast dynamic response and decentralized manufacturing based on local production, making the system easier to control as well as reducing the transport costs and environmental impacts. In this part, a self-supported catalyst bimetallic NiCu modified 3D printed electrode based on acrylonitrile butadiene styrene was fabricated for zinc-nitrate batteries through typical electroless plating. The morphology, structure and compositions of this electrode were characterized by a series of technologies including X-ray diffraction, X-ray photoelectron spectroscopy and electron microscopy. Besides, the catalytic activity, selectivity and stability of the as-prepared electrode and the battery performance of the ZNBs were carefully investigated. The results demonstrated that the as constructed ZNBs enabled reliable energy supply and continuous ammonia production. Furthermore, another catalyst was prepared for selective electrocatalytic reduction of nitrite to ammonia. Through a three-step synthetic route, the ruthenium atoms were incorporated into a copper nanowire structure, which demonstrated impressive electrocatalytic activity and selectivity. The integration of this catalyst into an aqueous zinc-nitrite battery also verified the technological utility of the electrode system. Through these studies, a range of advanced materials and methods have been discussed, highlighting the significance of rational design, targeted synthesis, state-of-the-art characterization as well as practical applications. In doing so, this thesis will serve to promote the current understanding of EES technologies and push their further universal application.