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Modification of Surface States of Hematite-Based Photoanodes by Submonolayer of TiO2for Enhanced Solar Water Splitting

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Modification of Surface States of Hematite-Based Photoanodes by Submonolayer of TiO2for Enhanced Solar Water Splitting. / Palmolahti, Lauri; Ali-Löytty, Harri; Khan, Ramsha; Saari, Jesse; Tkachenko, Nikolai V.; Valden, Mika.

In: Journal of Physical Chemistry C, Vol. 124, No. 24, 2020, p. 13094-13101.

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@article{2e777e8a1802452faf17066f75446ebb,
title = "Modification of Surface States of Hematite-Based Photoanodes by Submonolayer of TiO2for Enhanced Solar Water Splitting",
abstract = "Surface states are inherently involved with photoelectrochemical (PEC) solar fuel production; some of them are beneficial and participate in the surface reactions, but some act as recombination centers and therefore limit the PEC efficiency. Surface treatments have been applied to modify the surface states, but interrelated effects of the treatments on both types of surface states have not been properly considered. This research examines the modification of the surface states on hematite-based photoanodes by atomic layer deposition of submonolayer amount of TiO2 and by postannealing treatments. Our results show that the postannealing causes diffusion of Ti deeper into the hematite surface layers, which leads to an increased saturation photocurrent and an anodic shift in the photocurrent onset potential. Without postannealing, the separate TiO2 phase on the hematite surface results in a second intermediate surface state and delayed charge carrier dynamics, i.e., passivation of the recombination surface states. It is evident by these results that the intermediate surface states observed with impedance spectroscopy in a PEC cell are directly involved in the surface reaction and not with the recombination surface states observed with ultrafast (picoseconds-nanoseconds) transient absorption spectroscopy in air. These results open new optimization strategies to control the beneficial and detrimental surface states independently.",
author = "Lauri Palmolahti and Harri Ali-L{\"o}ytty and Ramsha Khan and Jesse Saari and Tkachenko, {Nikolai V.} and Mika Valden",
year = "2020",
doi = "10.1021/acs.jpcc.0c00798",
language = "English",
volume = "124",
pages = "13094--13101",
journal = "Journal of Physical Chemistry C",
issn = "1932-7447",
publisher = "American Chemical Society ACS",
number = "24",

}

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TY - JOUR

T1 - Modification of Surface States of Hematite-Based Photoanodes by Submonolayer of TiO2for Enhanced Solar Water Splitting

AU - Palmolahti, Lauri

AU - Ali-Löytty, Harri

AU - Khan, Ramsha

AU - Saari, Jesse

AU - Tkachenko, Nikolai V.

AU - Valden, Mika

PY - 2020

Y1 - 2020

N2 - Surface states are inherently involved with photoelectrochemical (PEC) solar fuel production; some of them are beneficial and participate in the surface reactions, but some act as recombination centers and therefore limit the PEC efficiency. Surface treatments have been applied to modify the surface states, but interrelated effects of the treatments on both types of surface states have not been properly considered. This research examines the modification of the surface states on hematite-based photoanodes by atomic layer deposition of submonolayer amount of TiO2 and by postannealing treatments. Our results show that the postannealing causes diffusion of Ti deeper into the hematite surface layers, which leads to an increased saturation photocurrent and an anodic shift in the photocurrent onset potential. Without postannealing, the separate TiO2 phase on the hematite surface results in a second intermediate surface state and delayed charge carrier dynamics, i.e., passivation of the recombination surface states. It is evident by these results that the intermediate surface states observed with impedance spectroscopy in a PEC cell are directly involved in the surface reaction and not with the recombination surface states observed with ultrafast (picoseconds-nanoseconds) transient absorption spectroscopy in air. These results open new optimization strategies to control the beneficial and detrimental surface states independently.

AB - Surface states are inherently involved with photoelectrochemical (PEC) solar fuel production; some of them are beneficial and participate in the surface reactions, but some act as recombination centers and therefore limit the PEC efficiency. Surface treatments have been applied to modify the surface states, but interrelated effects of the treatments on both types of surface states have not been properly considered. This research examines the modification of the surface states on hematite-based photoanodes by atomic layer deposition of submonolayer amount of TiO2 and by postannealing treatments. Our results show that the postannealing causes diffusion of Ti deeper into the hematite surface layers, which leads to an increased saturation photocurrent and an anodic shift in the photocurrent onset potential. Without postannealing, the separate TiO2 phase on the hematite surface results in a second intermediate surface state and delayed charge carrier dynamics, i.e., passivation of the recombination surface states. It is evident by these results that the intermediate surface states observed with impedance spectroscopy in a PEC cell are directly involved in the surface reaction and not with the recombination surface states observed with ultrafast (picoseconds-nanoseconds) transient absorption spectroscopy in air. These results open new optimization strategies to control the beneficial and detrimental surface states independently.

U2 - 10.1021/acs.jpcc.0c00798

DO - 10.1021/acs.jpcc.0c00798

M3 - Article

VL - 124

SP - 13094

EP - 13101

JO - Journal of Physical Chemistry C

JF - Journal of Physical Chemistry C

SN - 1932-7447

IS - 24

ER -