Triple‐Phase Interfacial Freestanding Fluffy Pine Needle Structures for Efficient Self‐Powered Photoelectrocatalysis

Abstract Approximately 2 billion people still lack access to clean drinking water. Extensive efforts are underway to develop semiconductor photocatalysts for water disinfection and environmental remediation, but conventional liquid‐solid diphase interfacial photocatalysts face challenges like low diffusion coefficients and limited solubility of dissolved oxygen. This study introduces freestanding copper oxide fluffy pine needle structures (CO‐FPNs) with tunable water pollutants‐gas‐solid (WGS) triple‐phase interfaces that enhance oxygen enrichment and reactive oxygen species (ROS) production. Three differently structured CO‐FPNs—microdendrites, hierarchical dendrites, and nanowires—are designed. The hierarchical CO‐FPN/WGS, predominantly in the Cassie‐Wenzel coexistence state, showed a 1.81‐ to 1.91‐fold higher reaction rate than the micro‐ and nanostructured CO‐FPNs due to increased interfacial O₂ levels and high adsorption capability. Under illumination, the hierarchical CO‐FPN/WGS achieved 99.999% sterilization by preventing pathogen adhesion and enhancing ROS generation. Additionally, a self‐powered photoelectrocatalytic system is constructed using nickel‐iron oxide‐deposited bismuth vanadate (NiFeO/BiVO₄) with hierarchical CO‐FPN/WGS, achieving 1.45 times higher than the hierarchical CO‐FPN/WGS alone, due to superior oxidation kinetics of NiFeO/BiVO₄ and improved oxygen reduction via atmospheric oxygen from the hierarchical CO‐FPN/WGS. This study demonstrates the first example of a triple‐phase interfacial self‐powered platform for efficient photoelectrocatalysis.