Researchers at the Indian Institute of Technology, Guwahati, have developed catalysts that help splitting of water directly using sunlight, without electricity.
Researchers Professor Mohammad Qureshi said in a press release issued today, “We have developed a ternary catalyst that comprises cobalt-tin layered-double hydroxides (LDH) and bismuth vanadate, which forms a p-n junction semiconductor with graphene bridges, and have shown that the catalyst, when used as a photoanode, is able to split water easily to produce hydrogen and oxygen.”
When light falls on the anode of a PEC cell, negatively charged electrons and positively charged holes are generated (excitons). In the absence of a catalyst, the thermodynamic barrier will be very high to overcome, hence cannot split the water into hydrogen and oxygen.
In order to split water, the holes must be prevented from recombining with the electrons, or in other words they should efficiency separate and get transported to the surface of the semiconductor. In the ternary catalyst system developed by the IIT Guwahati team, the bismuth vanadate generates electrons and holes in response to sunlight.
Graphene siphons the holes away from the vanadate and transports them into the cobalt-tin LDH, thus preventing their recombination with the electrons. The holes and the electrons are now available to split the water into hydrogen and oxygen.
The photocurrent density of the ternary photoanode is three-fold higher than when using the bismuth vanadate by itself because of the extraction and transportation of the holes by graphene. These researchers believe that their findings would help us understand the mechanism of hetero-structured photoanodes and inspire the design of cheaper photoelectrode systems for improved water oxidations.
The researchers are now in the process of developing a prototype device to test their photoanode in practical PEC cells.
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