The Structural Properties and Photoelectrocatalytic Response of Mn-Doped Hematite Photoanodes Prepared via a Modified Electrodeposition Approach

The concept of nanostructuring and doping of hematite (α-Fe₂O₃) photoanodes have been widely engaged towards improving their photoelectrocatalytic (PEC) response. Here, a FeCl₃-based solution was modified with 0–10 % polyethylene glycol (PEG) 400 and used as an electrolyte for the electrodeposition of nanostructured α-Fe₂O₃ thin films. The electrolyte containing 10 % PEG was further used to prepare Mn-doped α-Fe₂O₃ films by adding 1, 3, 6, and 10 % of MnCl₂.4H₂O with respect to the molarity of FeCl₃. The addition of 10 % PEG into the electrolyte limited particle agglomeration and yielded the best PEC response among the pristine films. The 3 % Mn-doped α-Fe₂O₃ photoanodes produced the highest photocurrent, yielding 2.2 and 6.1-fold photocurrent enhancement at 1.23 V and 1.5 V vs. RHE respectively, over the pristine films. The improved PEC response is linked to the reduced particle agglomeration and improved charge transport properties observed for the films. Density functional theory (DFT) calculations of the formation energies yielded negative values for the Mn-doped α-Fe₂O₃, which implies that the materials are thermodynamically stable after doping. This work introduces a new pathway for the electrodeposition of doped α-Fe₂O₃ films and underscores the roles of Mn-doping in boosting their PEC response.