For the first time, hematite (α-Fe2O3) crystals were electrochemically deposited over vertically
aligned conductive zinc oxide nanorods (NR) to form a specially designed 3D heterostructure
with a unique triple layer structure. The structure formed with a thin layer of ZnFe2O4
sandwiched between the hematite and the ZnO, which forms a barrier to reduce the back
migration of holes. Hence, the charge separation is significantly improved. The small unequal
bandgaps of α-Fe2O3 and ZnFe2O4 help to enhance and broaden visible light absorption. The
electron transportation was further improved by yttrium doping in the ZnO (YZnO) NRs,
resulting in increased conductivity. This allowed the vertically aligned NRs to perform as
electron highways, which also behave as effective optical waveguides for improved light
trapping and absorption, since ZnO absorbs little visible light. All these benefits made the unique
structures suitable for high performance photoelectrochemical (PEC) water splitting.
Optimisation of α-Fe2O3 thickness led to a photocurrent density improvement from 0.66 to
0.95 mA cm−2 at 1.23 VRHE. This was further improved to 1.59 mA cm−2 by annealing at
550 °C for 3 h, representing a record-breaking photocurrent for α-Fe2O3/ZnO systems. Finally
IPCE confirmed the successful generation and transfer of photoelectrons under visible light
excitation in the specifically designed heterostructure photoanode, with 5% efficiency for blue
light, and 15% for violet light