Novel Prussian Blue Analogous and Its Derived Material for Energy Storage and Energy Conversion

Abstract

Prussian blue analogs (PBAs) have a history of more than 100 years and have a significant impact on the comprehension of inorganic chemistry and materials. Due to the advantages of tunable chemical compositions, abundant redox-active sites, strong structural stability, and low cost, PBAs have been widely studied in many fields including energy storage and energy conversion. However, PBAs always suffer from the vacancies caused by water molecules, which will impact the structure stability, etc. In addition, PBAs also face the problem of low specific surface area, which will limit the exposure of the active site, so as to limit its development. In order to solve these problems, developing PBAs is significantly important. Herein, this thesis is aimed at developing PBAs materials and adjusting the morphology and structure of PBAs to enhance the performance of energy storage or energy conversion. The research contents and achievements of this project are as follows:

1. By utilizing the facile co-precipitation technique, a range of two-dimensional PBA nanosheets were synthesized, comprising single-metal CoCo nanosheets and multi-metal CuFe, CuCeFe, and CuCeCo nanosheets. Within the synthesized 2D PBA nanostructures, the CoCo nanosheets exhibit potential as anode materials for lithium-ion batteries, showcasing significantly enhanced specific capacity, improved rate performance, and superior stability compared to conventional CoCo cubes. In specific, the CoCo nanosheets demonstrate a reversible capacity of around 810.4 mAh g^-1 at 100 mA g^-1, surpassing most of the previously reported results. What is more, through serials of methods such as thermogravimetric analysis (TGA), electrochemical measurements and X-ray absorption fine structure (XAFS) characterization to study the mechanism of the superior performance of CoCo nanosheets over CoCo cubes toward high-performance lithium storage.

2. For the first time, the copper-cobalt Prussian blue analogue with unconventional hexagonal phase and prism-liked morphology (denoted as the H-CuCo) is synthesized. This phase H-CuCo PBA demonstrates a different lattice structure from the conventional cubic phase CuCo PBA, and a large amount of opened and unsaturated Cu site. Furthermore, via doping strategy, serials of hexagonal phase CuCo PBA with doping by Co, Fe, Ni, and Zn respectively are synthesized, and the amount of the unsaturated Cu atoms and the morphology of the hexagonal phase CuCo PBA are modulated.

3. Based on the hexagonal phase CuCo PBA prims method, adjusting the synthesis procedure, the CuCo PBA hexagonal sheets with the hexagonal phase (hp CuCo sheets) is prepared. With large amounts of unsaturated Cu sites, the hexagonal phase CuCo PBA plates deliver much better nitrate reduction to ammonia performance, 17 times than the conventional CuCo cubic PBA. In addition, the mechanism of high efficiency of electrosynthesis ammonia by nitrate reduction for the hexagonal phase CuCo PBA plates is studied via serials of methods.

4. The hexagonal phase CuCo PBA prism serves as the template, the CuO/Co₃O₄ prism with large amounts of cation vacancies is synthesized by the pyrolysis method. In this work, after pyrolysis CuCo PBA prism, the morphology of the prism can be maintained, and the inner of the prepared CuO/Co₃O₄ prism is compact instead of inner aggregation to cause morphology decomposing. In addition, via serial methods such as HRTEM and XAFS, the cation vacancies are characterized. What is more, the CuO/Co₃O₄ prism with cation vacancies shows impressive activity for nitrate reduction to ammonia. By in-situ measurements, the mechanism for high-efficiency electrocatalysis nitrate reduction to ammonia is revealed.

Date of Award	20 Aug 2024
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Zhanxi FAN (Supervisor)