Water-splitting photoelectrodes consisting of heterojunctions of carbon nitride with a p -type low bandgap double perovskite oxide

Quinary and senary non-stoichiometric double perovskites such as Ba₂Ca_0.66Nb_1.34-xFe_xO_6-δ(BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO₂reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba₂Ca_0.66Nb_0.68Fe_0.33Co_0.33O_6-δ(BCNFCo), exhibited an optical absorption edge at ∼800 nm,p-type conduction and a distinct photoresponse up to 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C₃N₄(CN) was prepared via a facile solvent-assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C₃N₄followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskites and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm^-2for sunlight-driven water-splitting with a Faradaic efficiency as high as ∼88%.