Hierarchical polymeric carbon nitride/poly(triazine imide) heterojunction film with benchmark photoelectrochemical water splitting efficiency

Carbon nitride family materials have attracted extensive attention for their applications in photocatalytic solar energy conversion. However, their progress in photoelectrochemical cell is limited by inefficient charge separation and difficulty in synthesis of heterojunction photoanode. Herein, a hierarchical polymeric carbon nitride /poly(triazine) imide (CN/PTI) photoanode was synthesized by pre-introducing CN into monomer film prior to thermal condensation. The pre-introduced CN ensures uniform photoanode synthesis, induces growth of PTI arrays, and provides scaffold for heterojunction fabrication, ultimately leading to hierarchical photoanode architecture composed of vertical PTI nanoflakes grown beneath and surficial carbon-doped CN layer on top. Photoelectronic studies confirm the extended light absorption, improved conductivity, and effective heterojunctions within the CN/PTI photoanode. Consequently, it produces benchmark photocurrent of 1.64 mA·cm⁻² at 1.23 V under 1-SUN illumination in 0.1 M KOH, with H₂ production rate of 1.96 μmol·cm⁻²·h. The IPCE values at 420 nm and 450 nm reach 75 % and 52 %, respectively. In triethanolamine-containing solution, the photocurrent is up to 2.34 mA·cm⁻² with IPCE of 95 % at 420 nm. This work unlocks benchmark photoelectrochemical performance by hierarchical CN/PTI photoanode via rationally designed architecture with heterojunction interfaces, and showcases the potential of photoanode structure design to achieve efficient photoelectrochemical water splitting.