Cation exchange process on copper selenide for HER/OER catalyst

• Main Author: Li, Jiuwei
• Other Authors: Alex Yan Qingyu
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: Engineering::Materials
• Online Access: https://hdl.handle.net/10356/104613; http://hdl.handle.net/10220/50139
• Institution: Nanyang Technological University

Although fossil fuels play a crucial role in modern society, the burning of fossil fuels will cause air pollution and emitter of carbon greenhouse gases such as carbon dioxide (CO2). Meanwhile, the increasing demand for energy in today’s society makes fossil energy insufficient. Therefore it’s necessary and urgent demand for sustainable and environmental friendly energy supply. Hydrogen has attracted people’s attention because of the outstanding conversion efficiency without generation of greenhouse gases. It can be produced by splitting of water with the help of electrocatalyst. Currently, high-efficiency catalysts are made of precious metals, for instance the platinum and iridium oxide for hydrogen evolution (HER) and oxygen evolution reaction (OER). However, the shortage and expensive prices prevent their widespread application in modern industry. Thus, developing a commercial catalyst with high efficiency to replace expensive precious metal-based catalysts and increase electrochemical reaction efficiency is an urgent thing. Non-precious metal catalysts with two-dimensional nanosheets structure are the most commonly used in catalytic electrolysis in recent years due to the relatively large exposed active area and stability compared with other nanomaterials. Here CuSe was selected to synthesize CuSe-CoSe nanosheets through cation exchange (CE) reaction. Firstly, we try to synthesize ultrathin CuSe nanosheet since traditional CuSe materials with poor HER and OER activity are rarely reported. It’s believed that the relatively large exposed active area of the nanosheets structure material can faster the mass transfer rate and facilitate the gas generated by the reaction to rapidly escape from the surface of the electrode. And nanosheet is stable compared with other nano materials, which means it would be difficult to destroy the structure during violent electrochemical reaction. An environmentally friendly and economical organic solution phase method was adopted to fabricated CuSe nanosheet. Secondly, cobalt will be introduced to CuSe precursor to enhance HER and OER performance of pure CuSe nanosheet by forming CuSe-CoSe nanosheets heterostructure. In one hand, Co-based catalysts are still considered to be one of the most likely alternatives to noble metal electrode catalysts because of their excellent performances towards HER and OER. In the other hand, the synergistic effect between copper and cobalt in heterostructures can increase the activity. To preserve the morphology of former nanosheet structure of CuSe, cation exchange (CE) reaction was used here. In the article, the effects of temperatures and reaction times can be explored with varying preparing conditions. Furthermore, the morphology and the phase were analyzed by Field Emission Scanning Electron Microscope (FESEM) and High-resolution transmission electron microscopy (HRTEM). Energy Dispersion X-ray (EDX) and X-ray diffraction (XRD) instrument would be used to determine the composition and element contents. Hydrogen and oxygen evolution performances were also tested for these materials to investigate whether the special heterostructure enhanced electrochemical properties comparing with pure copper selenide.