Theoretical design of highly active SrTiO3-based photocatalysts by a codoping scheme towards solar energy utilization for hydrogen production

Abstract

SrTiO 3 is a promising photocatalyst for the production of hydrogen from water splitting under solar light. Cr doping is an effective treatment for adjusting its absorption edge to the visible-light range, although the performance of Cr-doped SrTiO 3 is strongly affected by the oxidation number of the Cr ions. In this study, we theoretically predict that elevating the Fermi level, i.e., n-type carrier doping in SrTiO 3 , can stabilize the desirable oxidation number of chromium (Cr 3+), contributing to a higher activity for H 2 evolution. Our computational results, based on hybrid density-functional calculations, reveal that such an n-type condition is realized by substituting group-V metals (Ta, Sb, and Nb), group-III metals (La and Y), and fluorine atoms for the Ti, Sr, and O sites in SrTiO 3 , respectively. From our systematic study of the capability of each dopant, we conclude that La is the most effective donor for stabilizing Cr 3+. This prediction is successfully evidenced by experiments showing that the La and Cr codoped SrTiO 3 dramatically increases the amount of H 2 gas evolved from water under visible-light irradiation, which demonstrates that our guiding principle based on Fermi level tuning by the codoping scheme is valid for the design of advanced photocatalysts.

Photocatalytic H2 production from spinels ZnGa2−Cr O4 (0≤x≤2) solid solutions

“…Such a deviation of photocatalytic activity from light absorption implies that other factors might dominate the catalytic performance at high Cr content. According to XPS analysis above, this is likely due to the enrichment of Cr at the surface in sample ZnGa 0.5 Cr 1.5 O 4 as Cr is treated as an active element in many photocatalytic systems [22,24,25]. A plot of hydrogen evolution rate with the amount of Cr at the surface according to XPS clearly shows the positive effect of Cr (Fig.…”

“…It is known that the physical and chemical properties of host materials are significantly altered by the amount of dopants and optimized doping content is often seen for the photocatalytic performance of host semiconductors [19][20][21][22]. Since chromium has generally been served as a low cost dopant for the modification of various wide band gap semiconductors [20,[22][23][24][25][26], the comparable ionic radius between Cr 3 þ (0.615 Å) and Ga 3 þ (0.62 Å) strongly implies the possible formation of wide range solid solution of chromium in ZnGa 2 O 4 [27,28]. More importantly, ZnCr 2 O 4 has been reported to exhibit high photocatalytic hydrogen production [17], it is therefore very interesting to investigate the photocatalytic activity of Cr doped ZnGa 2 O 4 .…”

High-performance heterostructured CdS/Ba1−xSrxTiO3 system with unique synergism for photocatalytic H2 evolution

“…Titanium-based perovskite oxides such as ATiO 3 (A = Ba and Sr) have been investigated as a class of promising photocatalysts [18]. Attempts were made to improve the photocatalytic activity of BaTiO 3 and SrTiO 3 through doping them with metals or non-metals or creating heterojunctions [19].…”

Comparing Pt/SrTiO3 to Rh/SrTiO3 for hydrogen photocatalytic production from ethanol

“…Numerous works have addressed the photo-catalytic activity of SrTiO 3 alone, with other transition metals as well as doped with other ions [5][6][7][8][9][10][11]. Results differ strongly from one study to the other due to difference in crystallinity, metal dispersion, effect of dopant and reaction conditions.…”

“…A recent computational study (using the hybrid DFT method) of doping SrTiO 3 with metal cations coupled with experimental study showed that co-doping Cr and La ions had considerable enhancement effect on hydrogen production of water/methanol solution [11]. The reason invoked is that doping with La ions raised the Fermi level of Cr ions and stabilizes its oxidation state of Cr 3?…”