Hematite (Fe₂O₃) is a promising photoanode towards photoelectrochemical (PEC) water oxidation, but its efficiency is hampered by low conductivity and slow surface kinetics. To overcome this, we successfully explored the surface modification of Fe₂O₃ photoanodes with the electrodeposited amorphous MnO_x co-catalyst having unique nano-fibrous globe-like morphology. MnO_x overcoated Fe₂O₃ with optimized MnO_x thickness demonstrates the enhanced efficiency towards PEC water splitting, showing four-fold enhancement in its photocurrent density as compared to bare Fe₂O₃ thin films. Various physico chemical and electrochemical characterizations were conducted to unravel the role of amorphous MnO_x co-catalyst over Fe₂O₃ surface. Results suggest that this enhancement is mainly due to four important factors: (i) An increase in ECSA due to the nano-fibrous morphology of MnO_x over layers, (ii) the growth of amorphous MnO_x resulting in an increased number of electro-catalytically active centers, (iii) the formation of p-n junction (between p-type MnO_x and n-type Fe₂O₃) at the interface that reduces interfacial charge transfer resistance, and (iv) the presence of Mn with multiple oxidation states, viz. Mn³⁺ and Mn⁴⁺, in MnO_x that plays a significant role in water oxidation reaction. We believe that the presented methodology would be helpful for modifying other semiconductors’ surfaces (particularly with n-type conductivity) with amorphous p-type MnO_x nanofibrous structures for enhanced PEC water splitting activities.

Keywords: Photoelectrochemical (PEC) water splitting, Hematite (Fe₂O₃), MnO_x amorphous co-catalyst, shunting effect, nano-fibrous morphology.