Boron Doping of Metal-Doped Hematite for Reduced Surface Recombination in Water Splitting

Abstract

We report that metal ions (M: Sn4+ and Ti4+) and boron-codoped hematite photoanodes with an n–n+ homojunction showed significantly increased photoelectrochemical (PEC) water splitting activity with greatly reduced surface recombination. The secondary B-doping of broadly used M-doped hematite photoanodes not only suppresses the number of M+ ions, which inevitably cause electron–hole pair (EHP) recombination, but also generates an internal electric field for easy hole extraction. Taking advantage of these effects, the maximum length (500–600 nm) of hematite, which has the reported highest PEC performance, was increased to up to 900 nm in M:B-Fe2O, which in turn increased the active area of the photoanode. The M:B-Fe2O3 with a film thickness of 900 nm and a diameter of 122 nm converted the incident photons to EHPs with substantially reduced recombination and exhibited a photocurrent density of 1.92 mA/cm2 at 1.23 VRHE. After loading inexpensive oxygen evolution reaction catalysts (FeOOH) on the surface of M:B-Fe2O3, the photocurrent density of FeOOH/M:B-Fe2O3 reached 2.35 mA/cm2 at 1.23 VRHE. The cost-effective strategy of B-doping into M-doped hematite provides a straightforward way to address the M-doping-related negative effects, such as a high electron–hole recombination rate on the surface of hematite, and thus the critical length limitation of an ideal hematite photoanode, to potentially improve the performance of PEC devices.

Gradient tantalum-doped hematite homojunction photoanode improves both photocurrents and turn-on voltage for solar water splitting

“…Third, the preservation of high electrical conductivity in the bulk (by high concentration Ta 5+ dopants) promotes the rapid separation of photogenerated charge carriers. Besides, n + -n homojunction by heavily and slightly doped Ta 5+ in the core and shell parts provides a supplemental charge separation by an increased built-in electric field 39 . Finally, the gradient Ta dopants benefits the smooth flow of the separated charge carriers as schematically shown in Supplementary Fig.…”

Engineering surface states of hematite based photoanodes for boosting photoelectrochemical water splitting

“…[117] Plenty of attention has been drawn to the development of composite hematite photoanodes with doping or secondary semiconductors, to further enhance the PEC water oxidation efficiency. [106][107][108][109][110][111][112][113][114][115][116] Meanwhile, other researchers spared no effort in correlating PEC performance improvement with the surface states evolution upon doping or coating of a secondary semiconductor onto hematite photoanodes. [117][118][119][120][121][122][123][124][125][126][127][128] For instance, D. Monllor-Satoca et al prepared mesoporous hematite-titania composite films by mixing the respective preformed nanoparticles obtained by a non-aqueous solgel route in a wide range of loading levels (0-20 mol %).…”

Revealing the synergy of Sn insertion in hematite for next‐generation solar water splitting nanoceramics

“…The presence of natural mineral reserves and mining activity represents an advantage if hematite is used in PEC photoanodes, since the demand could be supplied by the countries that explore iron sources. To overcome well‐known intrinsic deficiencies of hematite associated with their electronic limitation that make the real response fall short of the predicted theoretical efficiency into solar to hydrogen conversion, different elements, such as: Ti, 18 V, 19 Sb, 20,21 P, 22 Cr, 23 B, 24,25 Ge, 26 and Sn, 27–32 and combinations like Nb‐Sn, 33 Ti‐Mg, 34 and Co‐Sn, 35 have been successfully employed. Sn has been highlighted as a potential modifier for this semiconductor polycrystalline ceramic, since it has been reported as able to improve the separation of photogenerated charges, achieving the highest photocurrent values among hematite photoanodes with different morphologies 36–38 .…”