IIT Mandi, IIT Delhi develop catalyst for solar-powered production of green hydrogen

A multi-Institutional team from IIT Mandi, IIT Delhi and Yogi Vemana University have replicated the structure of leaf in a low-cost inorganic catalyst to enable light-induced production of green hydrogen and ammonia.  

Results of their recent work, a team led by Associate Professor Venkata Krishnan, School of Basic Sciences, IIT Mandi, has published an article in the Journal of Materials Chemistry A. “We have been interested in improving the efficiency of photocatalytic processes for the production of hydrogen and ammonia because these two substances are industrially important,” said Dr Krishnan. Hydrogen is a green energy source and ammonia is the backbone of the fertiliser industry. Both hydrogen and ammonia are being manufactured through processes that consume large amounts of energy in the form of heat and also release greenhouse gases. The use of photocatalysis in the production of these two chemicals can save not only energy and costs, but also have significant environmental benefits. 

The researchers have addressed the main bottlenecks of photocatalysis – poor light absorption, photogenerated charge recombination and the need for catalytically active sites to use sunlight effectively to drive chemical reactions. They have improved the properties of a low cost photocatalyst, calcium titanate through an approach called ‘defect engineering’ and have shown its efficacy in producing green hydrogen and ammonia in two light-driven reactions. 

Specifically, the defect engineering was done by incorporation of oxygen vacancies in a controlled manner. These oxygen vacancies act as catalytically active sites to promote the surface reactions and thereby enhance the photocatalytic performance.  “We were inspired by the light harvesting mechanism of leaves and replicated the surface and internal three-dimensional microstructures of the leaf of the Peepul tree in the calcium titanate to enhance the light harvesting properties,” said the lead researcher.  This way, they improved the efficiency of light absorption. In addition, the introduction of defects in the form of oxygen vacancies helped to solve the problem of recombination of photogenerated charges. 

The scientists studied the structural and morphological stability of the defect engineered photocatalyst and showed that their photocatalyst showed excellent structural stability as the engineered oxygen vacancy defects were well-retained after recyclability studies. They used the catalyst to produce hydrogen from water and ammonia from nitrogen, using the sun’s rays as the activator at ambient temperatures and pressures. 

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