Janus 2D materials can harvest abundant hydrogen fuel
(Nanowerk News) Several studies have suggested that water splitting reactions could be catalyzed by a particular group of 2D materials – each only a few atoms thick. One particularly promising group is named Janus 2D materials, the two sides of which each display a different molecular composition.
Through new calculations detailed in EPJ B (“Janus AsXY (X=Se, Te; Y=Br, I) Two Dimensional Two Dimensions for Photocatalytic Water Splitting”), Junfeng Ren and colleagues at Shandong Normal University in China presented a new batch of four Janus 2D materials, which are well suited for the task.
Because hydrogen releases an enormous amount of energy when burned, with only water as a by-product, hydrogen is now widely viewed as an excellent alternative to fossil fuels. The splitting of a water molecule involves a ‘redox reaction’, in which electrons and holes participate in reduction and oxidation reactions.
Because it is an excellent semiconductor, the Janus 2D material is well suited to catalyze this reaction. When an electron in the insulating ‘valence band’ of a semiconductor absorbs a photon, it is excited into the ‘conduction band’ of the material, leaving behind a positively charged hole.
In turn, these materials act as sources and acceptors of electrons – allowing redox reactions to occur more easily.
In their theoretical study, Ren’s team examined this group of four materials: with one surface composed of selenium or tellurium, and the other of bromine or iodine – with both sides flanking a middle layer of astatine. In these semiconductors, the valence and conduction band energies are far enough apart to prevent electrons and holes from easily recombining: allowing them to combine electrons and holes to produce hydrogen and oxygen.
With all four materials showing excellent stability and light absorption, the researchers believe they could be very promising candidates for catalyzing water-splitting reactions. If these results can be reproduced in experiments, Ren’s team hopes the four ingredients can become key elements of global efforts to eliminate our carbon emissions in the coming decades.
