Metal-Organic Frameworks Derived Electrochemical Devices

Promovendus/a: Xuan Zhang

Promotor(en): Prof. dr. ir. Jan Fransaer, De heer Jiangshui Luo

Our daily life is rife with electrochemical devices: batteries, electrochemical capacitors, fuel cells, electrochromic windows and displays, Grätzel solar cells,…. The demand for conventional electrochemical devices keeps increasing at a fast pace. For example, the global lithium-ion battery market was valued at 22.8 billion USD in 2016 and expected to reach 93.1 billion USD by 2025. Likewise, the supercapacitor market will grow to 2.18 billion USD by 2022 at an annual growth rate of 21 % between 2016 and 2022 (568.2 Million USD in 2015). In the future, considering the current rush in renewable energy systems and the pressing global CO2 emission reductions, electrochemical devices such as , metal-air and metal-sulfur batteries, sodium batteries, water splitting electrolyzes and electrochemical synthesis cells will continue to grow. In view of this, there is a strong demand for more efficient electrochemical devices. The core of all electrochemical devices are their electrodes, and hence the performance of these devices is largely determined by these electrodes. The performance of these electrodes in turn depends on the electroactivity of the electrode materials and the techniques for preparing the electrodes. On the one hand, the bottlenecks of these electrochemical materials are the kinetically sluggish multi-electron transfer reactions (e.g oxygen reduction reaction for fuel cell and metal-air battery) and the high-cost of these electroactive materials (e.g Pt for oxygen reduction reaction). Metal-organic frameworks (MOFs), constructed from metal ions or clusters bridged by organic ligands, have been considered as ideal self-sacrificial templates for metal-carbon nanomaterials due to their highly ordered cavities, open channels and rational composition and structure These unique characteristics of MOFs allow them to serve as both template and precursor materials (metal and carbon). On the other hand, the conventional technique for preparing the electrodes involves several time-consuming steps and addition of polymer binder, which decreases the effective number of active sites and increases the cost. Seamlessly electrodes could be the solution for binder issues. Therefore, this PhD thesis addresses these two aspects, through the following tasks:

(1) Construction of effective and cheap electro-active materials and increase the number of active sites per mass/volume of electrode: A series of BTC linker based MOFs are designed and prepared by changing the pillars in these MOFs to works as a model platform for exploring the influence of MOF units (i.e. organic ligands, metal units and interactions of these two parts) on key parameters of MOF-derived materials. Depending on understanding the influence of MOF units on key parameters of MOF-derived materials, suitable electroactive materials for specific devices are designed.

(2) Investigation of new methods to seamlessly integrate composite electro-active materials into electrodes: In-situ synthesis of MOF derived materials is highly recommended for electrochemical (or photoelectric) devices not only because of the enhancement of reactivity and easy recycling but also to avoid binder issues. We proposed a universal strategy for the in-situ synthesis of carbon–metal oxide composite electrode by electrodeposition.