Mirabbos Hojamberdiev, Ronald Vargas, Zukhra C. Kadirova, Kosaku

Kato, Hadi Sena, Aleksei G. Krasnov, Akira Yamakata, Katsuya

Teshima, Martin Lerch

Unfolding the role of B site-selective doping of

aliovalent cations on enhancing sacrificial visible

light-induced photocatalytic H2 and O2 evolution

over BaTaO2N

Open Access via institutional repository of Technische Universität Berlin

Document type

Hojamberdiev, M., Vargas, R., Kadirova, Z. C., Kato, K., Sena, H., Krasnov, A. G., Yamakata, A., Teshima, K.,

Lerch, M. (2022). Unfolding the Role of B Site-Selective Doping of Aliovalent Cations on Enhancing Sacrificial

Visible Light-Induced Photocatalytic H2 and O2 Evolution over BaTaO2N. In ACS Catalysis (Vol. 12, Issue 2,

pp. 1403–1414). American Chemical Society (ACS). https://doi.org/10.1021/acscatal.1c04547.

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*Corresponding author: E-mail addresses: khujamberdiev@tu-berlin.de and hmirabbos@gmail.com

(M. Hojamberdiev)

2

Doping of foreign cations and anions is one of the effective strategies for engineering the defects and

modulating the optical, electronic, and surface properties that directly govern the photocatalytic O2

and H2 evolution reactions. BaTaO2N (BTON) is a promising 600-nm-class photocatalyst because of

its absorption of visible light up to 660 nm, small band gap (Eg= 1.9 eV), appropriate valence band-

edge position for oxygen evolution, good stability under light irradiation in concentrated alkaline

solutions, and nontoxicity. Although the photocatalytic and photoelectrochemical water splitting

efficiencies of BaTaO2N have been progressively improved, it is still far from the requirements set

the optical, electronic, and surface properties. Also, molecular dynamics (MD) is used to gain insights

into the respective effect of cation doping on adsorption energy of water molecules and formed

intermediates (H* for H2 evolution and HO*, O* and HOO* for O2 evolution) on the BaTaO2N

surfaces terminated with TaO6, TaN6, and TaO4N2 octahedra. Finally, the experimental reaction rates

for H2 and O2 evolution are correlated well using a linear energy-performance relationship,

elucidating the doping and surface-termination trends observed in the BaTaO2N photocatalysts.

modeling; Adsorption energy

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1. INTRODUCTION

Unlike their oxide counterparts, mixed-anion compounds exhibit unique electronic and atomic

photoelectrochemical, dielectric, and magneto-resistive properties that are sensitive to the surface

gap (Eg= 1.9 eV), appropriate valence band-edge position for oxygen evolution achieved by a 4-

electron transfer (4HO– → 4e– + 2H2O + O2), good stability under light irradiation in concentrated

alkaline solutions, and nontoxicity.11 The Co cocatalyst-modified BaTaO2N photoanode prepared by

a particle transfer method generated a photocurrent of 4.2 mA∙cm–2 at 1.2 V vs. reversible hydrogen

electrode (RHE) under simulated sunlight.12 The FeNiOx cocatalyst-modified Ta3N5-

nanorods/BaTaO2N photoanode fabricated by combining glancing angle deposition and dip coating

techniques yielded a photocurrent of ~4.5 mA∙cm–2 at 1.2 V vs. RHE under simulated sunlight.13 The

CoOx-deposited BaTaO2N/Ta2N/Ta photoanodes produced a photocurrent of 4.6 mA∙cm–2 at 1.2 V vs.

RHE and exhibited a 9% IPCE at 600 nm during water oxidation under simulated sunlight.14 Further,

an unprecedented photocurrent of 6.5 mA∙cm–2 at 1.23 V vs. RHE was achieved for Ar-annealed

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precursors, controlling the exposed surface, engineering an effective cocatalyst, etc. For instance,

Maeda and Domen16 achieved the solar water splitting to produce H2 and O2 above 660 nm using a

BaZrO3‐BaTaO2N solid solution as an anode material in a photoelectrochemical cell with an external

bias of 1.0 V (vs. Pt). BaTaO2N synthesized from the nitridation of (Na1/4Ba3/4)(Zn1/4Ta3/4)O3

exhibited an enhanced oxygen evolution activity with an apparent quantum yield of 11.9% at 420

nm.17 A one-step NH3-assisted flux growth method was demonstrated to enhance the water-splitting

activity of BaTaO2N via reducing the defect density, which is generally resulted from a long high-

temperature nitridation.18,19 Recent studies on the effect of different exposed surfaces found that the

BaTaO2N crystals with well-developed {111} facets20 and co-exposed {100} and {110} facets21 can

exhibit a significantly enhanced photocatalytic activity for H2 evolution in comparison to the

physicochemical and photophysical properties by an intentional introduction of foreign cations with

different radii and valences into the A-site and/or B-site of AB(O,N)3 and ABO3 perovskite hosts. In

this way, the band-edge position, optical absorption, charge density, charge mobility, charge

separation, electrical conductivity, defect density, etc. can be modified to combat low water-splitting

efficiency.23 The SrCl2 flux-mediated Al doping in SrTiO3 resulted in an apparent quantum efficiency

of 30% at 360 nm in the overall water splitting reaction.24 Recently, Mg-modified BaTaO2N exhibited

an apparent quantum efficiency as high as 2.59% at 420±20 nm due to the stronger Ta–O/N bonds,

lower concentration of Ta4+ defects, and positive shift of band-edge positions.25 The partial

substitution of Ta5+ cations in BaTaO2N by higher valent Mo6+ was found to increase the donor density

effectively, enhancing the photoelectrochemical water splitting under visible light irradiation.26 On