The development can lead to a carbon-free hydrogen economy as hydrogen is a clean and high-energy fuel that can be stored and used as needed. The findings have been published in the prestigious peer-reviewed Journal of Physical Chemistry Letters published by the American Chemical Society.
According to the research team, worldwide efforts in developing clean energy have been propelled by the ever-increasing need for energy accompanied by the dwindling reserve of fossil fuels which are also harmful for the environment.
"Since the discovery of the photovoltaic effect by Edmond Becquerel in 1839, conversion of solar energy into electrical power or chemical fuel has captured the interest and imagination of scientists. Solar energy is considered the most promising of the clean and renewable energy today," said Mohammad Qureshi, a professor at IIT Guwahati's chemistry department.
"The commonly known solar cells convert light directly into electrical energy. There is another type of sunlight-powered energy conversion system called PhotoElectroChemical (PEC) cells that have elicited attention in recent times due to their direct production of fuels in combination with electrical energy," he said.
Qureshi explained that PEC cells use solar energy to split simple and safe compounds such as water into hydrogen and oxygen. With hydrogen being a high-energy fuel that can be stored and used as needed, these cells are therefore considered the 'Holy Grail' of a carbon-free hydrogen economy. Despite the promise, PEC cells are not yet a practical solution to the energy crisis because of scientific bottlenecks such as the sluggishness of the water-oxidation process.
"Catalysts are used to activate the water-splitting process. These catalysts are expensive metals such as platinum, iridium and ruthenium, among others, which render the cells impractical," Qureshi said.
"We have developed a ternary catalyst that comprises cobalt-tin layered double hydroxides and bismuth vanadate, which forms a p-n junction semiconductor with graphene bridges. We have shown that the catalyst, when used as a photoanode, can split water easily to produce hydrogen and oxygen," he added.
Another member of the research team, Suhaib Alam, explained that 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. We are now in the process of developing a prototype device to test their photoanode in practical PEC cells," Alam added.