High Water-Splitting Efficiency through Intentional In and Sn Codoping in Hematite Photoanodes

Abstract

The effects of intermittent thin ITO layers on the water-splitting efficiency of α-Fe2O3 films grown by PECVD on FTO substrates are reported. The α-Fe2O3 was codoped with indium and tin by temperature-driven ionic transport and diffusion from the ultrathin ITO layer sputtered between the α-Fe2O3 layer and FTO substrate. The α-Fe2O3/ITO/FTO photoanodes showed a remarkable interdependence between the thickness of the ITO layer and PEC efficiency. Hematite photoanodes with a 32 nm thick ITO underlayer showed the highest photocurrent density of 2.5 mA cm–2, corresponding to an approximate 3-fold enhancement over pristine α-Fe2O3 at 1.23 V vs RHE, whereas the thinner (8 nm) ITO underlayer yielded the lowest onset potential at 0.6 V vs RHE. Although the electrode with a thicker 72 nm ITO underlayer showed a higher onset potential of 0.9 V vs RHE, it still showed an enhancement in the photocurrent density at higher bias voltages. α-Fe2O3 was also deposited on metallic titanium substrates with intermittent sputtered tin and ITO layers. The codoping with indium and tin from ITO was observed to yield greatly enhanced performance when compared with both α-Fe2O3 alone and tin-doped α-Fe2O3. Transient absorption decays in the sub-nanosecond time scale were not affected by the doping, indicating that the doping had little effect on the primary charge carrier generation and recombination. On the other hand, fewer trapped electrons on the microsecond to millisecond time scale and a greatly increased amount of long-lived surface photoholes were observed for the ITO-doped samples. The transient absorption results imply that the large increases in photoelectrochemical efficiency were obtained due to higher electron mobility, which reduces recombination and leads to more efficient electron extraction from the electrodes.

Ti, Zn co-doped hematite photoanode for solar driven photoelectrochemical water oxidation

“…Several modifications have been developed to ameliorate it, including the construction of passivation layers [10] , catalyst loading [18] , and building heterojunction [19,20] . Bimetallic doping is an important and facile way to elevate the conductivity and reduce recombination simultaneously [21][22][23] . Jun Wang et al .…”

“…Ali et al . [22] fabricated In, Sn co-doped hematite by inserting an ITO layer and demonstrated that they can reduce the recombination of electrons and holes. Si, Ti [23] and Sn, Zr [24] codoped hematite had also been investigated before.…”

Probing the dynamics of photogenerated holes in doped hematite photoanodes for solar water splitting using transient absorption spectroscopy

“…Element doping (i.e., addition of Ti, Si, Pt, Sn, P and Zr) [8][9][10][11][12][13][14][15][16][17][18] has been recognized as an efficient and widely used method to enhance the PEC activities of hematite photoanodes. For example, the dopant of Pt may have different states to play multiple roles in enhancing the PEC activity, 10 and non-metallic P doping can enhance the electron mobility, thus improving the PEC activity.…”

A facile surface passivation of hematite photoanodes with molybdate overlayers for efficient PEC water oxidation

“…For instance, indium and tin elements were codoped into α-Fe 2 O 3 by temperature-driven ionic diffusion from the ultrathin ITO layer which was sputtered on the FTO substrate. It was found that a 32 nm thick ITO underlayer exhibited 3-fold photocurrent enhancement over pristine hematite at 1.23 V vs. RHE [34].…”