Laser-Induced Graphene-Based Materials for Electrochemical Energy Storage and Conversion

The ever-increasing demand for clean energy has led to extensive research on the development of renewable energy technologies for energy storage and conversion, such as electrochemical capacitors, lithium-ion batteries, fuel cells, photo/electrical water splitting, and rechargeable metal-O2 batteries. This thesis focused on the development of laser-induced graphene (LIG) derived materials and devices for electrochemical energy storage and conversion. LIG is a 3D porous graphene material fused to a flexible substrate that is prepared by a one-step laser scribing process on commercial polyimide (PI) film. The LIG derived from PI is highly porous and is easily synthesized under ambient conditions in a scalable process. This thesis covers the design, synthesis, characterization and mechanistic study of LIG derived devices and catalysts in 5 chapters: Chapter 1 discusses the study on the all-solid-state, flexible, symmetric, and asymmetric LIG microsupercapacitors which are fabricated by a simple method in a scalable fashion from LIG on commercial polyimide films, followed by the electrodeposition of active materials on the interdigitated in‐plane architectures. These microsupercapacitors demonstrate comparable energy density to commercial lithium thin‐film batteries, yet exhibit more than two orders of magnitude higher power density with good mechanical flexibility. Chapter 2 describes the LIG-based electrodes with good activity for full water splitting and presents a water electrolyzer where H2 and O2 are simultaneously generated on either side of the plastic sheet and can thereby be selectively captured. In the rechargeable metal-O2 batteries, the cathode reactions (OER/ORR) often show significantly sluggish kinetics such as high overpotential and high Tafel slope. Therefore, I also focused on the LIG derived catalysts for the oxygen electrocatalysis. In Chapter 3, the oxidation of LIG by O2 plasma to form oxidized LIG boosts its performance in both OER and ORR, resulting in an enhanced activity towards rechargeable Li-O2 battery. In Chapter 4, I worked with collaborators and developed a distinctive method to prepare metal oxide/LIG composites as efficient catalysts for water oxidation (OER). Unlike the conventional methods, such as solvo-/hydro-thermal, thermal pyrolysis or chemical vapor deposition processes, my method synthesizes the NiFe-based catalysts through a facile laser scribing process without any tedious procedures. The LIG method is further developed to prepare bifunctional catalysts for metal-O2 batteries as shown in Chapter 5. The catalysts exhibited high activity in both Li-O2 and Zn-air batteries. It is worth noting that this method is newly developed, and its application is still expanding. We would anticipate that the method could be applied for the synthesis of a variety of metal-based catalysts for different reactions, and the dimension of metal species would be ranging from nanoparticles to sub-nano scale such as atomically dispersed supported metal catalysts, and even to metal-free heteroatom-doped LIG, with properly selected precursors and procedures.