Halide and Oxide Double Perovskites As Promising Semiconductor Photocatalysts Candidates for Artificial Photosynthesis of Solar Fuels
Authors: Mahmoud Idris Mohammed Ahmed 
Published: November 2022

Abstract

Artificial photosynthesis of solar fuels is deemed as one of the Holy grails of renewable energy technology for simultaneously solving energy and environmental issues. At the present, it is one of the most involved programs in the international Mission Innovation Challenge for Accelerating the Clean Energy Revolution. Solar-driven water splitting and CO2 conversion are the main research application of artificial photosynthesis. However, these reactions are extremely challenging due to energetically uphill (G>0) and non-spontaneous multi-electron transfer processes, which are difficult to be understood by traditional knowledge of catalysis. An efficient solar energy conversion system must simultaneously deal well with light absorption, charge separation and transfer, surface redox reactions. Particularly, efficient charge separation and transfer by retarding back electron transfer, are often regarded as the key determining steps for overall solar energy conversion. To solve the high recombination rates of photogenerated electron-hole pairs and their low reduction and oxidation abilities in a single photocatalyst, heterojunction manipulation is urgently required. Two mainstream heterojunctions—type-II and Z-scheme heterojunctions have been widely acknowledged [1].
Recently, lead halide perovskites (LHPs) with the chemical formula of ABX3, where A is an organic or inorganic cation (A= Cs+, MA+, FA+), B is Pb2+, and X is a halogen anion (Br-, Cl-, I-), such as CH3NH3PbI3,FAPbI3, and CsPbBr3 have been widely investigated as auspicious semiconductor photocatalysts for photocatalytic H2 production and photocatalytic CO2 reduction owing to their impressive photoelectrochemical properties, facile to synthesize, high carrier mobility, low exciton binding energy, and long carrier lifetime [2]. However, the high toxicity and notorious instability upon exposure to light, moisture, and high temperature are the major obstacles to their practical use.Therefore, developing alternative lead-free semiconductor photocatalysts with similar optoelectronic properties to the LHPs is highly needed.
Inorganic halide double-perovskites and analogous oxide double-perovskites with the chemical formula of A2B'B"X6 and A2B'B"O6, respectively, are layered 3D materials, which have been considered as a novel ecofriendly visible light responsive semiconductor photocatalysts to replace the toxic lead-halide perovskite. The main feature of the halide and oxide double-perovskites is that their structures can be accommodated with different transition metal combinations on B' and B" site cations to tune their intrinsic properties such as light absorption, carrier mobilities, chemical diversity, and so on. Theoretically, an auspicious photocatalytic activity can be realized from them owing to their impressive photophysical properties. However, poor charge separation and severe charge recombination have restricted their practical photocatalytic application. Recently, several halides and oxides double perovskites have been demonstrated as visible light-responsive photocatalysts for photocatalytic CO2 reduction and photocatalytic half-reaction (oxygen and hydrogen evolution reactions) such as Cs2AgBrBr6, Cs2AgSbBr6, Sr2CoTaO6, Sr2CoWO6, etc. [3-5]. However, for oxide double perovskites even though they have shown bifunctional photocatalytic oxygen and hydrogen two half-reactions with visible light but their potential as photocatalytic CO2 reduction and one-step overall water splitting have not been achieved so far. Therefore, further improvement of the material design and synthesis by assembling heterostructure based on two eco-friendly halide and oxide double perovskites may play a key role in achieving high efficient photocatalytic performance under visible-light-irradiation. Thought is a challenging task, but holds great potential in advancing science and technology in photocatalysis.

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