Combined Theoretical and Experimental Investigations of Atomic Doping To Enhance Photon Absorption and Carrier Transport of LaFeO₃ Photocathodes

Abstract

Perovskite-type lanthanum iron oxide, LaFeO3, is a p-type semiconductor that can achieve overall water splitting using visible light while maintaining photostability. These features make LaFeO3 a promising photocathode candidate for various photoelectrochemical cells. Currently, the photoelectrochemical performance of a LaFeO3 photocathode is mainly limited by considerable bulk electron–hole recombination. This study reports a combined theoretical and experimental investigation on the atomic doping of LaFeO3, in particular, substitutional doping of La3+ with K+, to increase its charge-transport properties and decrease electron–hole recombination. The computational results show that K-doping enhances not only the charge-transport properties but also photon absorption below the bandgap energy of the pristine LaFeO3. The effect of K-doping was systematically investigated by comparing the electronic and atomic structures, majority carrier density, hole-polaron formation, and optical properties of pristine and K-doped LaFeO3. The computational results were then verified by experimentally characterizing the crystal structures, compositions, optical properties, and photoelectrochemical properties of LaFeO3 and K-doped LaFeO3 electrodes. For this purpose, pristine LaFeO3 and K-doped LaFeO3 were prepared as high-surface-area, high-purity photoelectrodes having the same morphology to accurately and unambiguously evaluate the effect of K-doping. The combined computational and experimental investigations presented in this study provide useful insights into the effect of composition tuning of LaFeO3 and other p-type oxides with a perovskite structure.

Nanostructured LaFeO3 Photocathodes with Onset Potentials for the Hydrogen Evolution Reaction Over 1.4 V vs. RHE

“…11 Celorrio et al reported photovoltages as high as 1.2 V vs. RHE for the hydrogen evolution reaction at LaFeO 3 (LFO). 12 Other studies involving LaFeO 3 [13][14][15][16][17] and YFeO 3 18 have also observed high photovoltages but EQE less than 1%. The origin of carrier losses remains to be fully elucidated.…”

High Interfacial Hole‐Transfer Efficiency at GaFeO3 Thin Film Photoanodes

“…[ 9 ] Other ferrite photoanodes include ZnFe 2 O 4 , MgFe 2 O 4 , and CuFe 2 O 4 , achieving external quantum efficiency values of close to 10% and photocurrent onset potentials ranging from 0.6 up to 1 V. [ 10,11 ] Ferrite photocathodes such as LaFeO 3 and YFeO 3 have shown very interesting photovoltages for the hydrogen evolution reaction, but their activity is limited by bulk and surface recombination losses. [ 12–17 ] Ferroelectric materials such as BiFeO 3 and Bi 2 FeCrO 6 show complex PEC properties that have been linked to ferroelectric domains. [ 18,19 ] For instance, BiFeO 3 exhibits both n‐ and p‐type conductivity, including above photovoltages larger than the bandgap.…”

Strategies for the deposition of LaFeO3 photocathodes: improving the photocurrent with a polymer template

“…33 In a more recent work, the same author demonstrated that with K doping, LFO photocathodes of high porosity were able to achieve À268 mA cm À2 at +0.6 V RHE , when compared with À124 mA cm À2 for pristine LFO in O 2 purged electrolyte. 34 LFO lms prepared by pulsed laser deposition (PLD) exhibited photocurrent values of À65 mA cm À2 at 0 V RHE under simulated sunlight (100 mW cm À2 ) in oxygen-containing electrolyte solutions. 35 LFO lms deposited by spray pyrolysis demonstrated a photocurrent density of À160 mA cm À2 at +0.26 V RHE under simulated sunlight (100 mW cm À2 ) and O 2 containing solution.…”