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Hydrogen peroxide (H₂O₂) is a versatile and environmentally friendly oxidant, yet its conventional anthraquinone-based production remains energy-intensive and environmentally taxing. Electrocatalytic H₂O₂ generation via the two-electron oxygen reduction reaction (2e⁻ ORR) offers a sustainable and decentralized alternative. However, its practical application is limited by challenges in selectivity, efficiency, and catalyst durability, particularly under acidic conditions. This thesis systematically investigates the design and evaluation of Pd-based electrocatalysts for efficient 2e⁻ ORR. In Chapter 5, Pd catalysts ranging from nanoparticles to sub-nanometer clusters and atomically dispersed species were synthesized to elucidate size-dependent effects. CO adsorption was employed as a site-specific probe to correlate adsorption strength with product distribution. The results demonstrate that isolated Pd sites with moderate CO binding energy exhibit enhanced H₂O₂ selectivity, offering insights into structure–selectivity relationships in Pd-based systems. To isolate the influence of extrinsic structural parameters on apparent catalytic behavior, Chapter 6 introduces Au-based catalysts as a model system to investigate the effects of interparticle distance, catalyst layer thickness, and mass transport phenomena. Both interparticle distance and catalyst layer thickness are identified as critical factors affecting intermediate diffusion, re-adsorption, and overall catalytic performance. During 2e⁻ ORR, reactive oxygen species (ROS) derived from H₂O₂ are unavoidably generated, posing a significant degradation risk to electrocatalysts. To directly assess chemical stability under such oxidative conditions, Chapter 7 introduces an H₂O₂ immersion protocol as a complementary method to conventional electrochemical stress testing. Applied to Pd₁Ac/C, the protocol revealed severe metal leaching and structural degradation, highlighting the vulnerability of conventional carbon-supported catalysts to ROS-induced damage. To address these limitations, heteroatom-doped hollow carbon spheres (HCS) were employed as advanced supports. Nitrogen and sulfur co-doping enhanced Pd anchoring, electronic stabilization, and resistance to oxidative degradation, substantially improving durability without compromising activity and selectivity. This work advances the fundamental understanding of H₂O₂ electrosynthesis by establishing structure–selectivity–stability relationships in isolated Pd catalysts supported on carbon. The resulting insights inform the rational design of efficient and robust electrocatalysts, supporting future development of scalable and sustainable H₂O₂ production technologies.