Photoelectrochemical water splitting by hematite boosted in a heterojunction with B-doped g-CN 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-Fe 2 O 3 ) and boron-doped graphitic carbon nitride (B-C 3 N 4 ). 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-Fe 2 O 3 and the O 2 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 × 10 19 cm −3 for the α-Fe 2 O 3 /B-C 3 N 4 /p-CNT photoanode, compared to α-Fe 2 O 3 and α-Fe 2 O 3 /B-C 3 N 4 . Superstructuring the B-C 3 N 4 and p-CNT onto pristine α-Fe 2 O 3 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-Fe 2 O 3 /B-C 3 N 4 heterojunction. Achieving such cost-effective, highly efficient hematite-based photoanodes offers an opportunity to fabricate tandem photoelectrochemical devices for low-cost solar fuel production. Enhanced PEC water splitting with an α-Fe 2 O 3 /B-C 3 N 4 type II heterojunction. Use of pyrolytic (p-)CNT to improve photoanodic current density. Improved electrical conductivity for facile charge separation & transfer. DFT hints at a Z-scheme mechanism.