Liquid-phase chemical reduction and supercritical hydrothermal synthesis of copper nanocrystals: advances in synthetic control, antioxidation strategies, and applications

Copper nanocrystals are promising materials for conductive pastes, printed electronics, catalysis, and energy-related devices because of their high electrical and thermal conductivity, catalytic activity, and low cost. However, their practical deployment remains limited by rapid oxidation, agglomeration, and the difficulty of simultaneously achieving synthetic controllability, oxidation resistance, and long-term functional stability. Although considerable progress has been made in the synthesis and surface protection of copper nanocrystals, the relationships among synthesis route, antioxidation design, and application-oriented performance have not yet been systematically integrated. This review addresses this gap by comparing two major synthetic routes, liquid-phase chemical reduction and supercritical hydrothermal synthesis, within a unified framework that connects synthetic control, oxidation resistance, and practical applicability. The nucleation and growth behavior of copper nanocrystals are first summarized, followed by an analysis of how reducing agents, precursors, stabilizers/protective agents, solvents, and supercritical reaction conditions affect particle size, morphology, crystal structure, and dispersion behavior. Major antioxidation strategies, including surface coating, crystal-plane reconstruction, and surface conversion, are then compared, with emphasis on their mechanisms and compatibility with low-temperature sintering, conductive interconnects, and long-term reliability. Representative applications in conductive materials, catalysis, and functional composites are further discussed to clarify how materials design governs practical performance. By linking synthesis variables with antioxidation mechanisms and application requirements, this review provides a more integrated perspective than previous method- or application-focused summaries. Finally, key challenges and future directions are highlighted, including scalable green synthesis, cleaner surface-protection strategies, mechanistic in situ characterization, and durability evaluation under service-relevant conditions.