Laser assisted manufacturing of nanomaterials for energy conversion
[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] With the rapid growth of global population and societal development, nonrenewable energy sources such as fossil fuels are being consumed at an alarming rate. Meanwhile, the environment is faced with a grand challenge due to the exploitation, processing, and utilization of these traditional fossil fuels. Therefore, it is of great importance to develop renewable and sustainable energy strategies, including energy storage and conversion. Among them, electrolyzer, hydrogen-based fuel cell and metal air battery have drawn much attention due to their high-efficient, renewability, environment-friendly. However, at present their performances highly depend on the noble metals based electrocatalysts which are not only scarce but also expensive. In order to lower the cost of abovementioned devices and facilitate their large-scale applications, it is necessary to develop high-efficient, low cost and stable electrocatalysts. So far, much effort has been devoted to developing earth-abundant element based electrocatalysts or lowering the use of the noble metals without compromising performance. These materials are developed by synthesis methods based on wet chemistry, which unavoidably involves tedious experiment steps, harsh reaction conditions, and costly capital investment. This dissertation focuses on investigating the laser assisted fabrication of nanocatalysts under ambient conditions, and exploring their applications in energy conversion, especially electrochemical water splitting. In contrast to traditional laser synthesis of nanomaterials in liquid or in vacuum which suffers from low yield and expensive experimental instruments, the developed CO2 laser based nanomanufacturing method has greater potentials for mass production. Chapter 1 introduces current challenges of electrolyzer, hydrogen-based fuel cell, and metal air battery as well as the proposed and demonstrated solutions. Much attention is paid to discuss merits and demerits of these solutions. Chapter 2 presents the synthesis of graphene from coal via one step laser scribing as multifunctional materials for joule heater, supercapacitor, an electrochemical dopamine sensor, and electrocatalyst. Next, Chapter 3 discusses the synthesis of laser induced MoS2/carbon and explores its catalytic activity toward hydrogen evolution reaction. In Chapter 4, a novel synthesis method of electrocatalysts has been reported by using polyimide derived laser induced graphene (LIG) as a microreactor and support. The obtained Pt/LIG and FeNi3/Fe3O4/LIG show superior catalytic activity toward hydrogen evolution reaction and oxygen evolution reaction, respectively. Benefited from the flexibility of the polyimide film and the simple synthesis method, a laser assisted roll to roll manufacturing method which is compatible with existing industrial protocols is proposed. Finally, in Chapter 5, by applying methodology shown in Chapter 4, supermolecules were explored as a novel precursor to produce electrocatalysts with much improved the catalytic activity.
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