Degree Type

Dissertation

Date of Award

2019

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

Major

Mechanical Engineering

First Advisor

Shan Hu

Abstract

The oxygen evolution reaction (OER) plays vital roles in electrochemical energy conversion and storage applications, including water-splitting systems, fuel cells, metal-air batteries, and CO2 reduction devices, but the development of highly active and robust OER catalysts based on non-noble metals by simple methods is challenging. In this dissertation, three major strategies are proposed for developing advanced OER electrocatalysts at low cost by simple and versatile methods. In the first work, a bimetallic Ni-Fe-P nanosheet arrays were designed and fabricated as a pre-catalyst to catalyzing super high OER current densities under alkaline and neutral media. To catalyze a 10 mA/cm2 OER current density, only 156 mV and 396 mV overpotentials are needed in 1 M potassium hydroxide (KOH) and 0.1 M phosphate buffer (KPi) electrolytes, respectively. Specific investigations were carried out of the Fe/Ni ratios, electronic structures, and the Ni oxidation properties for the OER activities. The second work brought the rarely reported metal fluoride hydroxyl to the view of community and studied the role of fluoride in the electrochemical cyclic voltammetry (CV) cycling, using Ni-Fe fluoride hydroxide nanosheet arrays (NiFe-OH-F) as the representative case. After ~ 200 CV cycles, the original NiFe-OH-F surface of ~ 30 nm depth was converted into mesoporous and amorphous NiFeOx layer, which shows a 58-fold increase in OER current density compared to the 1st CV cycle, at the overpotential of 220 mV. The third work reported a facile room temperature strategy to fabricating self-supported grain boundary (GB)-rich 2D metal hydroxide networks at large scale by etching the cobalt metal-organic framework (Co-MOF, ZIF-L-Co). In the etching process, the simultaneous linker removal and metal ions hydrolysis in Co-MOFs lead to the formation of 2D ultrathin and defective Co/CoNi hydroxide networks. The obtained catalysts have been proven among the most active OER catalysts to date. These strategies create more opportunities for developing more advanced electrode materials for the electrochemical energy conversion and storage systems.

Copyright Owner

Bowei Zhang

Language

en

File Format

application/pdf

File Size

113 pages

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