Hematite (α-Fe2O3) has been widely investigated as a promising material for
photoelectrochemical (PEC) water-splitting due to its abundance, stability, and favorable band
gap of 2.1 eV, with a theoretical 15% solar-to-hydrogen efficiency. Despite these desirable
properties, several challenges remain, including slow oxygen evolution reaction (OER) kinetics
and a mismatch between absorption depth and minority carrier collection length. Due to this
mismatch, nanostructured architectures are necessary to achieve large photocurrents.
Photoanodes of hematite-coated nanostructured scaffolds and thin films on F:SnO2 (FTO)
glass substrates were fabricated to investigate the effects of film thickness, interfaces, metallic
dopants, and nanostructured architecture on PEC water splitting. Hematite thin films were
fabricated by successive ionic layer adsorption and reaction (SILAR), where a substrate is
alternately immersed in iron-containing and oxidizing baths for a 0.5 nm growth rate per SILAR
cycle. Annealing at 775oC caused phase-transformation from iron-hydroxide to hematite and
diffusion of Sn from the FTO substrate into the hematite, which may increase film conductivity
and enhance OER kinetics.
Photocurrent increased with film thickness from heightened light absorption but
approached saturation at about 120 cycles due to charge collection limitations. Photocurrent was
further enhanced by adding an ultrathin (<10 nm) TiO2 interlayer between the FTO and hematite,
which likely improves the interface and reduces shunting. Depth-profiled XPS reveals that both
Ti and Sn diffuse through the hematite upon annealing. The surface is particularly rich in Ti,
which may passivate surface traps or catalyze OER kinetics.
To increase light absorption while maintaining hematite thickness similar to the
collection length, nanostructured inverse-opal Sb:SnO2 (ATO) scaffolds with hematite coatings
were prepared. This scaffold increased surface area by 85% compared to planar films, and
photocurrent increased by over 15%. Nanostructured architectures and interfacial treatments
following this approach will increase efficiency of PEC water splitting with hematite.
photoelectrochemical (PEC) water-splitting due to its abundance, stability, and favorable band
gap of 2.1 eV, with a theoretical 15% solar-to-hydrogen efficiency. Despite these desirable
properties, several challenges remain, including slow oxygen evolution reaction (OER) kinetics
and a mismatch between absorption depth and minority carrier collection length. Due to this
mismatch, nanostructured architectures are necessary to achieve large photocurrents.
Photoanodes of hematite-coated nanostructured scaffolds and thin films on F:SnO2 (FTO)
glass substrates were fabricated to investigate the effects of film thickness, interfaces, metallic
dopants, and nanostructured architecture on PEC water splitting. Hematite thin films were
fabricated by successive ionic layer adsorption and reaction (SILAR), where a substrate is
alternately immersed in iron-containing and oxidizing baths for a 0.5 nm growth rate per SILAR
cycle. Annealing at 775oC caused phase-transformation from iron-hydroxide to hematite and
diffusion of Sn from the FTO substrate into the hematite, which may increase film conductivity
and enhance OER kinetics.
Photocurrent increased with film thickness from heightened light absorption but
approached saturation at about 120 cycles due to charge collection limitations. Photocurrent was
further enhanced by adding an ultrathin (<10 nm) TiO2 interlayer between the FTO and hematite,
which likely improves the interface and reduces shunting. Depth-profiled XPS reveals that both
Ti and Sn diffuse through the hematite upon annealing. The surface is particularly rich in Ti,
which may passivate surface traps or catalyze OER kinetics.
To increase light absorption while maintaining hematite thickness similar to the
collection length, nanostructured inverse-opal Sb:SnO2 (ATO) scaffolds with hematite coatings
were prepared. This scaffold increased surface area by 85% compared to planar films, and
photocurrent increased by over 15%. Nanostructured architectures and interfacial treatments
following this approach will increase efficiency of PEC water splitting with hematite.