Epitaxial Growth\nof a Three-Dimensional Hollow and\nChestnut Shell Photothermal p–n Junction Photoanode

The p–n junction, a widely studied semiconductor\nmaterial\nstructure, offers only limited improvements in photoelectrochemical\n(PEC) efficiency. Herein, a three-dimensional (3D) p–n junction\nh-Ta<sub>3</sub>N<sub>5</sub>@CoN featuring a stable chestnut shell\nhollow sphere structure and photothermal effect was synthesized by\nusing an epitaxial growth strategy. The fine fibers within the sphere\ninduce Rayleigh scattering, which scatters unabsorbed light, thereby\nenabling secondary absorption and enhancing light utilization. The\nquantum confinement effects generated by CoN fine fibers, which are\nsized in a few nanometers, inhibit the recombination of electron–hole\npairs. Moreover, the lattice matching between Ta<sub>3</sub>N<sub>5</sub> and CoN allows for smoother movement of carriers and nonradiative\nrelaxation phonons along the lattice, thereby enhancing the transport\nof both carriers and heat. The obtained h-Ta<sub>3</sub>N<sub>5</sub>@CoN/FTO p–n junction photoanode, under near-infrared (NIR)\nauxiliary irradiation, demonstrates a photocurrent of 8.71 mA cm<sup>–2</sup> at 1.23 V<sub>RHE</sub>. Moreover, the h-Ta<sub>3</sub>N<sub>5</sub>@CoN+NIR/FTO photoanode can sustain operation for 168\nh, which, to my knowledge, surpasses the operational durations of\nall other Ta<sub>3</sub>N<sub>5</sub>-based photoanodes. This study\nsynthesizes three-dimensional hollow chestnut shell photothermal p–n\nheterojunctions through an epitaxial growth strategy, endowing the\nmaterial with a more efficient carrier separation and photothermal\ntransfer efficiency.