Epitaxial Growth of a Three-Dimensional Hollow and Chestnut Shell Photothermal p–n Junction Photoanode

The p-n junction, a widely studied semiconductor material structure, offers only limited improvements in photoelectrochemical (PEC) efficiency. Herein, a three-dimensional (3D) p-n junction h-Ta₃N₅@CoN featuring a stable chestnut shell hollow sphere structure and photothermal effect was synthesized by using an epitaxial growth strategy. The fine fibers within the sphere induce Rayleigh scattering, which scatters unabsorbed light, thereby enabling secondary absorption and enhancing light utilization. The quantum confinement effects generated by CoN fine fibers, which are sized in a few nanometers, inhibit the recombination of electron-hole pairs. Moreover, the lattice matching between Ta₃N₅ and CoN allows for smoother movement of carriers and nonradiative relaxation phonons along the lattice, thereby enhancing the transport of both carriers and heat. The obtained h-Ta₃N₅@CoN/FTO p-n junction photoanode, under near-infrared (NIR) auxiliary irradiation, demonstrates a photocurrent of 8.71 mA cm^-2 at 1.23 V_RHE. Moreover, the h-Ta₃N₅@CoN+NIR/FTO photoanode can sustain operation for 168 h, which, to my knowledge, surpasses the operational durations of all other Ta₃N₅-based photoanodes. This study synthesizes three-dimensional hollow chestnut shell photothermal p-n heterojunctions through an epitaxial growth strategy, endowing the material with a more efficient carrier separation and photothermal transfer efficiency.