Revealing the roles of surface treatments on hematite (α-Fe2O3) photoanode in the shift of the onset potential

•We investigated effects of various treatments on the onset potential shift of hematite.•We found that the enhanced charge transfer efficiency resulting from the catalyzed oxygen evolution reaction did not influence the shift of the turn on voltage significantly.•We were able to observe the significant cathodic shift of the onset potential of hematite treated with NiFeOx, which could be attributed to the enhancement of the charge separation efficiency.