Several investigations have suggested that particular groups of 2D materials, each only a few atoms thick, may be able to catalyze the water-splitting reaction. The so-called 2D Janus materials, whose two sides differ in their molecular make-up, are a particularly intriguing class.

Junfeng Ren and colleagues from Shandong Normal University in China introduce a new set of four 2D Janus materials using new calculations described in EPJ B that may be particularly well suited to this endeavor.

It is now well acknowledged that burning hydrogen produces an enormous amount of energy, with the only byproduct being water, making it a superior option to fossil fuels. A “redox reaction” called the splitting of water molecules involves both electrons and holes in reduction and oxidation processes. The 2D Janus materials are ideal catalysts for this process because they are excellent semiconductors. A positively charged hole is left behind when an electron in a semiconductor’s insulating “valence band” absorbs a photon and is stimulated into the “conduction band” of the substance. Redox reactions can take place more readily because of the dual roles played by these materials as an electron generator and a receiver.

Ren’s team analyzed a set of four of these materials in their theoretical study: one surface is made of selenium or tellurium, the other of bromine or iodine, and both sides are encircled by a layer of astatine in the centre. The energies of the valence and conduction bands in these semiconductors were sufficiently different to prohibit electrons and holes from readily recombining, allowing them to combine to produce hydrogen and oxygen.

The researchers think that all four materials could be exceptionally interesting candidates for accelerating the water-splitting reaction because they exhibit great stability and light absorption.