Aliovalent gallium dopants remove Ti 3+ defects and improve photocatalytic and photoelectrochemical water oxidation properties of LaTiO 2 N

Wang, Li [University of California, Davis, CA (United States)]; Kandel, Rajesh [University of California, Davis, CA (United States)]; Salmanion, Mahya [University of California, Davis, CA (United States)]; Rao, Guodong [University of California, Davis, CA (United States)] (ORCID:0000000180433436); Hahn, William [University of California, Davis, CA (United States)]; Najaf, Zainab [University of California, Davis, CA (United States)]; van Benthem, Klaus [University of California, Davis, CA (United States); University of Alabama, Tuscaloosa, AL (United States)]; Britt, R. David [University of California, Davis, CA (United States)] (ORCID:0000000308898436); Osterloh, Frank E. [University of California, Davis, CA (United States)] (ORCID:0000000292883407)

doi:10.1039/d6ta00050a

DOE OSTI · 3762394

Aliovalent gallium dopants remove Ti 3+ defects and improve photocatalytic and photoelectrochemical water oxidation properties of LaTiO 2 N

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Abstract

LaTiO 2 N is a promising semiconductor for the water splitting reaction due to its 2.1 eV band gap and stability against corrosion. However, its solar energy conversion is limited by Ti 3+ recombination defects introduced during ammonolysis. Here we show for the first time that Ti 3+ defects in LaTiO 2 N can be suppressed with incorporation of 2, 5, and 10% aliovalent gallium (Ga 3+ ) dopants during synthesis via the layered La 2 Ti 2 O 7 intermediate. Electron paramagnetic resonance (EPR) spectroscopy on the solid powders confirms a reduction in the Ti 3+ donor density from 2.97 × 10 17 cm −3 for the non-doped material to ∼6.24 × 10 16 cm −3 for 5% Ga-doped LaTiO 2 N. The remaining Ti 3+ defects are concentrated near the LaTiO 2 N surface, according to X-ray photoelectron spectroscopy. The defect reduction shifts the optical absorption edge from 2.02 to 2.09 eV and eliminates a broad absorption band at 1050 nm from the optical absorption spectra. It also removes a 1.0–1.7 eV sub-band gap photovoltage signal from surface photovoltage spectra. This suggests that empty Ti 3+ d-orbitals are located 1.0–1.7 eV above the LaTiO 2 N valence band edge. Removing these recombination states with increasing Ga 3+ content enhances the photoconversion efficiency of LaTiO 2 N during water oxidation. The optimized 2 wt% CoO x -loaded 5% Ga-doped LaTi O2 N material has a 16% AQE (400 nm) for O 2 production from aqueous silver nitrate solution and a ∼2.1 mA cm −2 water oxidation photocurrent at 1.23 V under 100 mW cm −2 Xe arc lamp illumination. The water oxidation photocurrent is stable during a 50 min test, and the Faraday efficiency for O 2 generation is 97%, confirming short-term corrosion stability of LaTiO 2 N. Altogether, these results provide a better understanding of the distribution, concentration, and impact of Ti 3+ defects on the optical, photovoltage, and photoelectrochemical properties of LaTiO 2 N. In combination with other defect control strategies, aliovalent Ga 3+ doping can help bring the solar energy conversion efficiency of LaTiO 2 N closer to the theoretical limit.

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Wang, Li [University of California, Davis, CA (United States)], Kandel, Rajesh [University of California, Davis, CA (United States)], Salmanion, Mahya [University of California, Davis, CA (United States)], Rao, Guodong [University of California, Davis, CA (United States)] (ORCID:0000000180433436), Hahn, William [University of California, Davis, CA (United States)], Najaf, Zainab [University of California, Davis, CA (United States)], van Benthem, Klaus [University of California, Davis, CA (United States); University of Alabama, Tuscaloosa, AL (United States)], Britt, R. David [University of California, Davis, CA (United States)] (ORCID:0000000308898436), Osterloh, Frank E. [University of California, Davis, CA (United States)] (ORCID:0000000292883407). 2026-01-01. Aliovalent gallium dopants remove Ti 3+ defects and improve photocatalytic and photoelectrochemical water oxidation properties of LaTiO 2 N. https://doi.org/10.1039/d6ta00050a

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