Promoting Photocatalytic Overall Water Splitting by Controlled Magnesium Incorporation in SrTiO₃ Photocatalysts

Abstract

SrTiO3 is a well‐known photocatalyst inducing overall water splitting when exposed to UV irradiation of wavelengths <370 nm. However, the apparent quantum efficiency of SrTiO3 is typically low, even when functionalized with nanoparticles of Pt or Ni@NiO. Here, we introduce a simple solid‐state preparation method to control the incorporation of magnesium into the perovskite structure of SrTiO3. After deposition of Pt or Ni@NiO, the photocatalytic water‐splitting efficiency of the Mg:SrTiOx composites is up to 20 times higher compared to SrTiO3 containing similar catalytic nanoparticles, and an apparent quantum yield (AQY) of 10 % can be obtained in the wavelength range of 300–400 nm. Detailed characterization of the Mg:SrTiOx composites revealed that Mg is likely substituting the tetravalent Ti ion, leading to a favorable surface–space–charge layer. This originates from tuning of the donor density in the cubic SrTiO3 structure by Mg incorporation and enables high oxygen‐evolution rates. Nevertheless, interfacing with an appropriate hydrogen evolution catalyst is mandatory and non‐trivial to obtain high‐performance in water splitting.

Photocatalytic overall water splitting using modified SrTiO3

“…17 Reaction (1) is accompanied by vast structural re-arrangement, yielding some remaining Ni embedded in Ni(OH)2. (Re-)illumination again converts Ni(OH)2 into NiOOH (hence the initial high hydrogen production rate after a dark period), and dark treatment again converts additional Ni according to reaction (1). As consequence of reactions (1) and (3) the metallic Ni content decreases with time (see XPS) and eventually metallic Ni will only be present in small quantities, if any.…”

“…The growth in energy demand of the world has recently been met by enhanced production of fossil-based fuels, including coal, oil, or gas (methane). 1,2 As shown in Figure 1.1, renewable resources constitute a relatively small fraction of the combined world energy consumption. 3 As a consequence, greenhouse gas emissions and environmental pollution have increased to unsustainable levels.…”

“…Solar-light utilization for photocatalytic overall water splitting (POWS) is a promising alternative to electrolysis to produce hydrogen, since photocatalytic water splitting is simple, and can be operated at low-cost. 1,4,7 Transformation and storage of solar energy in the form hydrogen can significantly reduce the rate of the greenhouse gas emissions. Given the lowcost and simplicity of photocatalytic hydrogen production, this thesis has focused on designing an efficient photocatalytic water splitting system.…”

“…Research on photocatalysis for water-splitting in slurry phase reactors, yielding hydrogen and oxygen, has focused on i) doping, creating optimized semiconductors for conversion of sunlight into excited states (holes and electrons), and ii) functionalizing (doped) semiconductor crystals with so-called co-catalyst nanoparticles to enhance the reaction rates of the necessary surface redox reactions (proton reduction and water oxidation) 1 . One of such co-catalyst systems that has attracted significant attention, is a composite of Ni/NiO particles.…”

“…Storing solar light to in chemical bonds is considered a feasible method to contribute to the energy transition from fossil to renewable sources. [1][2][3] To this end, semiconductor-based photocatalytic water splitting needs to be developed. 4,5 To date, various promising photocatalysts have been reported.…”