Electrochemically activated surface reconstruction of OER catalyst by Cr leaching

• Main Author: Lee, Jun Yan
• Other Authors: XU Zhichuan, Jason
• Format: Thesis-Master by Research
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Materials
• Online Access: https://hdl.handle.net/10356/137828
• Institution: Nanyang Technological University

Global demand for energy consumption has been on the rise over the years with globalization and population growth. However, the current usage of fossil fuel as our main energy source raised concerns over the impact on our environment. Hydrogen appears to be the ideal replacement with scalable water electrolysis from renewable energy sources. However, the sluggish kinetics of oxygen evolution reaction (OER) cause it to be expansive and hindered its usage. Therefore it is important to develop an efficient OER catalyst based on first row transition metals to make water oxidation economical. For many years, different transition metal based oxides OER catalyst like perovskite, spinels, layered hydroxides and amorphous oxides/hydroxides have been explored. Recently, surface amorphisation and reconstruction of the catalyst during electrochemical cycling through OER was discovered to boost the OER performance. To engineer and advance our understanding on in-situ surface reconstruction, Cr leaching phenomenon from CoCr2O4 was investigated. Various characterization techniques like CV, CA, ICP, XPS, XAS and TEM techniques were employed to study the active species of OER. The leaching of Cr created vacancies and defects and allowed the formation of CoOOH surface species and improved the OER performance. The future works have been proposed on defect and vacancy studies on a series of Co(3-x)CrxO4 nanoparticle or nanosheets through controlled leaching of Cr. DFT computation have suggested that there is a possibility of large oxygen vacancies that exist in the CoCr2O4 structure and contributed to surface reconstruction. To identify Cr leaching mechanism during OER, isotopic investigation of the O2 and Cr complexes by OLEMS was proposed as well. Overall, this work have recommended a bottom up approach to design and develop more efficient OER catalyst through surface reconstruction.