Photoelectrochemical water splitting by hematite boosted in a heterojunction with B-doped g-C₃N₄ nanosheets and carbon nanotubes

Here, we effectively layered economically viable pyrolytic carbon nanotubes (p-CNTs) as solid-state mediators to accelerate the charge carrier transfer between hematite (α-Fe₂O₃) and boron-doped graphitic carbon nitride (B-C₃N₄). This synergistic combination leads to higher photoelectrochemical water splitting performance with a photoanodic current density of 2.85 mA cm⁻², which is a 4.1-fold enhancement compared to pristine α-Fe₂O₃ and the O₂ evolution rate detected was 22.70 μmol h⁻¹ cm⁻² with a Faraday efficiency of ∼98% at 1.7 V_RHE. Mott-Schottky analysis confirms the highest donor density of 55.7 × 10¹⁹ cm⁻³ for the α-Fe₂O₃/B-C₃N₄/p-CNT photoanode, compared to α-Fe₂O₃ and α-Fe₂O₃/B-C₃N₄. Superstructuring the B-C₃N₄ and p-CNT onto pristine α-Fe₂O₃ enhances the charge separation and transfer efficiencies, and moreover mitigates recombination losses. DFT calculations suggest the type II charge transfer mechanism switched to an enhanced Z-scheme type by simple deposition of p-CNT on the α-Fe₂O₃/B-C₃N₄ heterojunction. Achieving such cost-effective, highly efficient hematite-based photoanodes offers an opportunity to fabricate tandem photoelectrochemical devices for low-cost solar fuel production.