The growing demand for efficient energy conversion technologies has compelled researchers to explore novel approaches for catalytic systems that can address the pressing global challenges associated with energy sustainability. The unique properties exhibited by nanomaterials, such as their unique electronic structure, high surface area, tailored morphology, and tunable surface chemistry, offer tremendous opportunities for optimizing their catalytic activity. Herein, my dissertation presents a comprehensive exploration of the design and synthesis of nanostructured catalysts, focusing on the principles of structural engineering to manipulate the composition, morphology, and surface properties of materials. Structural engineering plays a pivotal role in tailoring the properties of nanostructured catalysts, enabling the precise control of their electrochemical behavior, and enhancing their performance in energy conversion processes. By carefully designing the structure at the atomic and nanoscale levels, it becomes possible to optimize the catalysts' activity, stability, and selectivity, ultimately advancing the field of energy conversion and enabling the development of high-performance catalyst materials. Specifically, this dissertation will delve into the atomic structure of metal-nitrogen-carbon materials (Chapter 2 and 3), ultrafast synthesis of catalysts with non-equilibrium structures (Chapter 4-6), and the surface functionalization of nanoparticles/nanostructures by using conjugated alkyne ligands (Chapter 7 and 8):
Chapter 1 serves as an introductory chapter, providing a comprehensive overview of the fundamental ideas and principles in energy conversion, including the importance of electrocatalysis and the role of nanostructured catalysts. It sets the stage for the subsequent chapters, highlighting the significance of structural engineering for achieving high-performance catalysts. Meanwhile, some background review of metal-nitrogen-carbon nanomaterials, ultrafast synthesis, and the surface functionalization of materials are provided. Chapter 2 investigates the fabrication of metal-nitrogen-carbon (MNC) nanocomposites using a wet-impregnation procedure. The obtained Pd-HNC nanocomposites demonstrate superior ORR activity compared to metallic Pd nanoparticles and even outperform commercial Pt/C and relevant Pd-based catalysts. This highlights the effectiveness of atomic dispersion and surface enrichment of palladium in a carbon matrix. In Chapter 3, carbon nanocomposites based on transition-metal oxides are explored for the ORR. The introduction of dual metals (Ru and Fe) and nitrogen doping results in RuFe-NC nanocomposites with excellent ORR activity, rivaling commercial Pt/C benchmarks. The use of a trinuclear complex facilitates atomic dispersion of ruthenium within iron oxide nanoparticles, leading to enhanced ORR performance. Introducing dopants is also a very effective structural engineering method in improving the electrocatalytic activity of nanomaterials. Chapter 4 focuses on the use of ruthenium nanoparticles supported on carbon paper for the hydrogen evolution reaction (HER). The metallic Ru nanoparticles prepared using a novel magnetic induction heating (MIH) method exhibit remarkable HER activity, comparable to commercial Pt/C benchmarks. The surface metal-Cl species, which are hard to preserve in conventional heating methods, play a critical role in enhancing electrocatalytic activity. Chapter 5 explores the ultrafast preparation of cobalt/carbon nanocomposites using MIH. The resulting nanocomposites exhibit excellent oxygen evolution reaction (OER) performance, surpassing commercial RuO2. Charge transfer between the carbon scaffold and metal nanoparticles contributes to their superior catalytic activity. Operando x-ray absorption spectra (XAS) was employed to reveal the electrocatalytic mechanism that metallic Co nanoparticle would transform into CoOx species to act as active sites for OER. In Chapter 6, carbon-FeNi spinel oxide nanocomposites are synthesized using MIH-quenching, resulting in high-performance catalysts for the OER. The rapid heating and quenching process prevents phase segregation and produces a Cl-rich surface, contributing to the exceptional catalytic activity, confirmed both experimentally and theoretically. Chapter 7 investigates the design of bifunctional catalysts using 4-ethylphenylacetylene-functionalized iridium nanoparticles. The Ir-C≡ nanoparticles exhibit enhanced electrocatalytic activity for both HER and OER, surpassing commercial Ir/C and Pt/C benchmarks. The formation of Ir-C≡C- conjugated interfacial linkage enhances the electron density and interactions with reaction intermediates, leading to improved performance in electrochemical water splitting. In Chapter 8, a facile wet-chemistry procedure is reported for the preparation of stable CuOH nanostructures through deliberate functionalization with select organic ligands. The resulting CuOH nanostructures exhibit a nanoribbon morphology with embedded nanocrystals within an amorphous nanosheet-like scaffold. The functionalization with acetylene and mercapto derivatives forms Cu-C≡ and Cu-S- interfacial bonds, respectively, leading to effective electronic coupling at the ligand-core interface in the former case. The acetylene-capped CuOH nanostructures demonstrate enhanced photodynamic activity in inhibiting bacterial growth, attributed to reduced material bandgap and effective photocatalytic generation of reactive oxygen species.
