Shape-controlled silicon doped hematite nanostructures for enhanced PEC water splitting

Hematite (alpha-Fe2O3) is one of the most promising photoanode materials for photoelectrochemical (PEC) water splitting although great challenges hinder high performance. Silicon-doped alpha-Fe2O3 shows improved PEC activity but the relationship among dopant content and enhanced conductivity, structure, and particle morphology is only poorly understood. Here, we present a systematic study on hydrothermally grown alpha-Fe2O3 nanocrystals by using XRD, Raman, UV-vis spectroscopy, TEM, XPS, SQUID magnetometry, electrochemical impedance spectroscopy, and photocurrent measurements. We find that the Si content controls the morphology of alpha-Fe2O3 already at Si 5 at.% inducing a transition from nanostructures with ellipsoidal shape to nanowires. Si doping is effective in improving PEC activity in the case of Si1% at. sample, which shows a 20% photocurrent enhancement in comparison with pure alpha-Fe2O3. On the contrary, alpha-Fe2O3 containing Si content higher than 5 at.% presents lower PEC activity. Results are rationalized in the view of the interplay of morphological, structural, magnetic, and electronic properties in doped alpha-Fe2O3 thus providing general guidelines for the design of efficient photoelectrodes for solar water splitting.