Ni-, Co-, and Mn-Doped Fe₂O₃ Nano-Parallelepipeds for Oxygen Evolution

A unique synthesis route was developed to prepare different metal-doped iron oxide parallelepipeds via a low-temperature light-driven bottom-up chemistry approach devoid of any template molecule to be explored as an electrocatalyst in a basic medium for the oxygen evolution reaction (OER). We successfully prepared a hierarchical parallelepiped-like morphology of iron oxide (Fe2O3) and different transition-metal-doped M-Fe2O3, namely, Mn-doped iron oxide (Mn-Fe2O3), Co-doped iron oxide (Co-Fe2O3), and Ni-doped iron oxide (Ni-Fe2O3), and subsequently characterized them by diverse physical techniques. A closer inspection of the morphology clearly authenticated that the hierarchical parallelepiped-like morphology of M-Fe2O3 was evolved due to assembly of several small nanorods. We then studied their electrocatalytic activity toward OER and compared their activity during the OER process. All of the doped M-Fe2O3 exhibited enhanced catalytic activity compared to the pristine Fe2O3, owing to the synergistic effect of the doped metal together with Fe. Among all of the as-prepared catalysts, Ni-Fe2O3 showed outstanding stability and OER activity due to the higher electronegativity of Ni compared to that of Mn or Co. Finally, we had demonstrated how the doped metal enhanced the activity of the catalysts by tuning their electronegativity.