YFO photocathode fabricated via spray pyrolysis for unassisted solar water splitting for generation of hydrogen fuel†

Efficient solar to fuel conversion technology is highly desirable to meet future global renewable energy demands as conventional energy resources are environmentally irresponsible and depleting rapidly. Photoelectrochemical (PEC) water splitting without the use of any external potential bias and/or assistance to produce hydrogen (a clean and renewable fuel) is a technology having the potential to fulfil this desire. However, the main bottleneck is the unavailability of cost-effective, efficient and stable photoelectrodes, which are used to conduct water splitting using light photons. YFeO₃ (YFO) thin films with a small energy band gap (E_g), suitable band positions straddling water redox potential and high stability were fabricated using a simple, cost-effective and scalable synthesis technique i.e., spray pyrolysis. The optimum YFO film was applied, for the first time to the best of our knowledge, for generation of hydrogen fuel through water splitting without applying any external potential bias and/or assistance. Orthorhombic YFO (o-YFO) showed a maximum photocurrent of ∼0.65 mA cm⁻² at 0.46 V vs. RHE, faradaic efficiency of ∼70%, and excellent stability spanning over 6 hours. UV-visible and electrochemical impedance spectroscopy (EIS) revealed the p-type characteristic, narrow E_g of 2.45 eV and suitable band positions, which encompassed the redox potential of water, of the o-YFO film. The o-YFO film generated 0.41 µmol cm⁻² of hydrogen over 6 hours without any assistance in a spontaneous hydrogen evolution reaction (HER). In a subsequent cycle, it generated 0.35 µmol cm⁻² of hydrogen, showing its potential as a reusable photoelectrode in the HER. Post HER characterizations did not show any visible/significant changes in the phase and morphology of the o-YFO film, indicating its stability under the applied HER conditions.