KCl flux suppresses surface recombinations of hematite photoanode for water oxidation

Hematite is a promising photoanode for solar water splitting because of its favorable bandgap, excellent chemical stability and low cost. However, it suffers from both severe bulk and surface-charge recombinations, resulting in photoactivities much lower than the theoretical value. In this work, a facile new strategy is proposed by annealing hematite in the presence of potassium chloride (KCl) flux at 800°C. The photocurrent density of the annealed hematite, denoted ‘KCl-hematite’, increases from 0·34 mA/cm² for pristine hematite to 0·54 mA/cm² at 1·23 V_RHE and further to 0·90 mA/cm² after cobalt–phosphate (Co-Pi) deposition. Moreover, the photocurrent onset potential of KCl-hematite shows a cathodic shift of 120 mV compared with that of pristine hematite. It is demonstrated that potassium chloride flux can enhance the crystallinity and orderliness of hematite on the surface, reducing surface recombinations. This facile strategy by a flux offers a new insight to passivate surface recombinations of photoelectrodes and can be easily extended to other materials to enhance their photoactivities.