Extremely stable bare hematite photoanode for solar water splitting

Photoelectrodes that are efficient, highly stable, made from low cost materials and easily prepared using inexpensive techniques are required for commercially viable solar photoelectrochemical (PEC) water-splitting technology. Hematite is one of few materials that is being considered for this application. In this work, bare hematite thin films prepared by spray pyrolysis were systematically optimized following a design of experiments approach. A response surface methodology was applied to factors: (i) sprayed volume of solution; (ii) temperature of the glass substrate during the deposition; and (iii) time gap between sprays and the optimized operating conditions obtained were v=42 mL, T=425 °C and t=35 s. The optimized hematite photoelectrode showed a photocurrent density of ca. 0.94 mA cm−2 at 1.45 VRHE, without dopants or co-catalysts, which is remarkable for a thin film of ca. 19 nm. The stability of this photoelectrode was assessed over 1000 h of PEC operation under 1-sun of simulated sunlight. A record-breaking result was obtained with no evidences of hematite film degradation neither of current density loss. These results open the door to turn PEC cells into a competitive technology in the solar fuel economy.