전기촉매 강화를 위한 금속간 및 고엔트로피 합금 나노입자의 형상 및 조성에 관한 연구

Abstract

This dissertation focuses on the development of methods to control the morphologies and compositions of Pd-based nanoparticles for their application in electrocatalytic reactions. It explores their synthesis methods, as well as their physical, electronic, and electrochemical properties. The first chapter offers an overview of advancements in renewable energy related to Pd-based catalysts, strategies to enhance the catalytic performance of Pd-based materials, surface modifications of Pd-based catalysts, and research on nanomaterials and their utilization in electrocatalytic applications. Chapter two describes Pd based bimetallic nanocrystals (NCs) with low-coordinated surface atoms endow a tremendous ability to modify electronic properties and have the synergistic effect to improve electrocatalytic performance. Among various bimetallic NCs with different compositions, intermetallic Pd-Pb NCs can improve the poisoning tolerance of surface-active sites during electrocatalytic reactions. In addition, Pb can provide abundant oxygen-containing species (OHads) and has the ability to cleavage the C–C bond during electrocatalysis that can hinder the production of COads intermediate species, thereby improving ethanol oxidation reaction (EOR) performance. Herein, we report a wet-chemical method for synthesizing highly uniform Pd3Pb nanobranches (NBs). The growth process of Pd3Pb NBs was controlled using ascorbic acid as a reductant, oleylamine as a solvent, 1-octadecene as a surfactant, and ammonium bromide as a shape-directing agent. Their unique NB morphology makes them suitable as electrocatalysts, attributed to the effective adsorption of ethanol and (OH)ads and enhanced removal capability of intermediates adsorbed on the active site of Pd3Pb NBs due to the intermetallic Pd–Pb composition and high density of low-coordinated surface atoms in Pd3Pb branches that can enhance EOR in alkaline media. The prepared Pd3Pb NBs exhibited significantly higher mass activity than Pd3Pb nanocubes and commercial Pd/C catalysts. Chapter three deeply studies the cost-effective catalysts for the HER by substituting Pt to Ru in Pd- based catalyst. In this study, we investigate the size-dependent catalytic performance of Ru on intermetallic Pd3Pb NWs for HER, focusing on the role of single atoms, clusters, and nanoparticles. The synthesized Pd3Pb-RuX NWs (X: S, C, and N) exhibit distinct morphologies, with Ru atoms anchored on the NW surface. Through a facile synthetic method, the incorporation of Ru in various concentrations, producing Ru single atoms, clusters, and nanoparticles on Pd3Pb NWs. The electrocatalytic HER performance of these catalysts is evaluated, revealing that Pd3Pb-RuS NWs, with Ru single atom, exhibit superior activity, with a lower overpotential (13 mV) at 10 mA cm-2 compared to Pt/C (45 mV) and a lower Tafel slope (31 mV dec-1) than Pt/C (50 mV dec-1). The presence of Ru single atom on Pd3Pb NWs significantly enhances stability, with Pd3Pb-RuS NWs displaying minimal potential loss (5 mV) after 10,000 cycles. Detailed characterization elucidates the structural modifications induced by Ru decoration, highlighting the precise control achievable over nanoscale features. XRD, XPS, and XANES reveal the structural alterations and bonding environments resulting from Ru incorporation. Electrochemical impedance spectroscopy demonstrates enhanced charge transfer rates in Ru-decorated Pd3Pb NWs, contributing to improving HER activity. This study underscores the potential of size-dependent Ru modifications on intermetallic NWs as efficient electrocatalysts for HER, offering insights into catalyst design for sustainable energy applications. Chapter four focuses on Direct Alcohol Fuel Cells (DAFCs), which present a promising avenue for sustainable energy conversion, with ethanol emerging as a key fuel due to its high energy density and low toxicity. However, challenges persist in developing efficient electrocatalysts for ethanol oxidation, particularly in alkaline media. Intermetallic Pd3Pb nanocrystals have shown potential as electrocatalysts, with lead (Pb) enhancing catalytic activity. This study explores the impact of boron doping on Pd3Pb NWs, focusing on strain and ligand effects on ethanol oxidation. Boron incorporation induces tensile strain and alters surface electronic states, affecting the adsorption of reaction intermediates and influencing p-d orbital hybridization. The synthesized Pd3Pb-B NWs exhibit enhanced catalytic activity and selectivity for C1 products with a significant decrease in CO poisoning compared to Pd3Pb nanocubes and Pd/C. Mechanistic insights reveal a downshift in the d-band center, favoring C1 pathway selectivity by more than 50%. The superior performance and stability of Pd3Pb-B NWs underscores the potential of tailored strain and ligand effects in designing efficient electrocatalysts for ethanol oxidation in DAFCs and other energy systems. Chapter five discusses the controlling morphologies of high-entropy alloys (HEAs) for their potential applications in nanotechnology, particularly in catalysis for HER. This chapter explores the synthesis and characterization of PdPtFeCoNi HEA nanostructures, including NSs, NWs, and NPs, using a one- pot synthetic approach. The influence of various chemical reagents on the morphological evolution of these nanostructures is investigated, revealing insights into the tailored synthesis of HEA materials. The electrochemical performance of these nanostructures is evaluated for HER, demonstrating that PdPtFeCoNi HEA NSs and PdPtFeCoNi HEA NWs exhibit superior catalytic activity compared to PdPtFeCoNi HEA NPs, attributed to their increased active surface area, optimized hydrogen adsorption- desorption dynamics, enhanced mass transport, and structural stability. This study underscores the importance of nanoengineering strategies in developing efficient and durable electrocatalysts for sustainable energy applications.