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Density functional theory calculations are applied to study the influence of co-doping on the stability, electronic structure, and photocatalytic activity of tetragonal BaTiO 3 (001) surface. The results show that the formations of all the metal-nonmetal co-doped BaTiO 3 (metal = V, Nb, Ta, Mo, W and nonmetal = N, C) are energetically favorable. Most of co-doped surfaces have remarkable narrower bandgaps than the pristine surface, which favors the movement of absorption edge to the visible light region. Co-doped systems have better affinity toward H 2 O than the pure surface. For most of the studied systems, the active sites of HER and OER are the O site and the Ti site adjacent to the metal dopant, respectively. Surface co-doping results in remarkable decreases in | Δ G H | of HER and the OER overpotential of BaTiO 3 (001) surface. This work proposes the potential application of BaTiO 3 modified by surface co-doping as efficient photocatalysts for overall water splitting. Surface codoping in BaTiO 3 remarkably enhances the activities of HER and OER. [Display omitted] • Surface codoping can efficiently reduce the band gap of BaTiO 3. • Co-doped BaTiO 3 surfaces have better affinity toward H 2 O than the pure one. • Co-doped BaTiO 3 involving Mo or W remarkably improve the OER performance. • Co-doped surfaces exhibit higher activities in HER than the pure BaTiO 3 surface. [ABSTRACT FROM AUTHOR]

SrTiO 3 loaded with NiO cocatalyst is one of representative photocatalysts for overall water splitting, which have attracted considerable attention. However, the function of NiO particles in the photocatalytic system is still under debate. In this work, we present a theoretical investigation based on density functional theory calculations to reveal the origin of the high photocatalytic performance achieved by loading NiO onto SrTiO 3 surface. By considering two terminations of SrTiO 3 (001), the interfacial geometries, electronic structures, charge densities and optical absorptions of NiO(001)/SrTiO 3 (001) have been calculated. The interface including SrO-termination connecting with NiO(001) (NiO/SrO) has a stronger covalent interaction than the one including TiO 2 -termination connecting with NiO(001) (NiO/TiO 2). The analyses on electronic properties and charge redistributions indicate that the formation of interfacial structures reduces the effective masses of photoinduced carriers and results in a type-II band alignment, which is conducive to separate the photogenerated carriers into two components of the interface. The electrons gathering on SrTiO 3 side will take part in the hydrogen evolution reaction, while the holes accumulating on NiO side will participate in the oxygen evolution reaction. It is found that the geometrical reconstruction around the interface has no influence on the extension of absorption edge due to the characteristics of heterostructures with indirect band gap. This study reveals that NiO functions as the water oxidation cocatalyst to suppress the recombination of photoinduced electron and hole pairs, which leads to the enhancement of photocatalytic activity in SrTiO 3 system. NiO functions as the oxidation cocatalyst to suppress the recombination of photogenerated carriers and enhance the photocatalytic activity of SrTiO 3. Image 1 • The heterostructures have indirect gaps and faster mobilities of charge carriers. • The interface benefits the separate gathering of charge carriers on two components. • The internal electric field is a driving force for charge separation. • Our findings give reasonable explanations on the high activity of NiO/SrTiO 3. [ABSTRACT FROM AUTHOR]

NaTaO 3 loaded with NiO cocatalyst is one of the few photocatalysts for overall water splitting in UV region, which have attracted much attention. In this work, density functional theory calculations have been performed to investigate the interfacial geometries, electronic structures, charge transport, optical absorptions and band offsets of NiO(001)/NaTaO 3 (001) slab models. By considering possible terminations of NaTaO 3 (001) surface, two heterostructures denoted as NiO/TaO 2 and NiO/NaO have been constructed. Our results show that two kinds of contact are thermodynamically stable, and there is a stronger rumpling of atomic layers appearing in NiO/NaO than NiO/TaO 2. The calculated band structures reveal that NiO(001)/NaTaO 3 (001) interfaces have indirect band gaps. The mobilities of photoinduced charge carriers in interfacial structures are faster than those in pure surfaces. NiO/TaO 2 has a higher mobility and lower recombination rate of photogenerated electrons and holes than NiO/NaO. Loading NiO on NaTaO 3 surface has a negligible effect on the extension of light absorption, which is consistent with experiments. Both heterostructures form a Type-II band alignment. The difference of electrostatic potentials around the interface as a driving force boosts the migration of electrons and holes to different domains of the interface, which is beneficial to extend the lifetime of photoinduced carriers and improve the photocatalytic activity of NaTaO 3 system. NiO/TaO 2 has the ability of overall splitting water with NiO as the oxidation cocatalyst, while in NiO/NaO, the photogenerated electrons and holes are accumulated on NiO and NaO side, respectively. Our results demonstrate that the function of NiO in NiO/NaTaO 3 photocatalytic system is determined by the termination property of NaTaO 3 (001) surface, which may be one possible reason why it is difficult to ascertain whether NiO is a proton reduction cocatalyst or water oxidation cocatalyst experimentally. • The heterostructures have indirect gaps and faster mobilities of charge carriers. • The interface benefits the separate gathering of charge carriers on two components. • The different electrostatic potentials is a driving force for charge separation. • The contacting layer of NaTaO 3 (001) with NiO(001) is the key to the role of NiO. • Our findings give reasonable explanations on the high activity of NiO/NaTaO 3. [ABSTRACT FROM AUTHOR]