Catalysts have been an inevitable part of innumerable chemical reactions and play a major role in controlling the rate of a reaction. Platinum is one of the most prominent catalysts in most of the reactions due to its favorable electronic configuration and also its stability in harsh chemical environments. One such applications of platinum is as a catalyst in a fuel cell.
A fuel cell is an electrochemical energy conversion device which uses hydrogen and oxygen to produce clean electricity. In this era of ever increasing demand for energy and the fast depletion of non-renewable resources such as fossil fuels, fuel cell has been hailed as a promising source of renewable energy.
The fuel cell is powered by simple reactions. The amount of power produced relies heavily upon the rate of reactions. Platinum plays a significant and efficient role in catalyzing the reactions viz. hydrogen oxidation reaction at anode and oxygen reduction reaction at the cathode.
The major disadvantages of platinum is its scarcity and high cost and hence an affordable fuel cell is still a distant dream. These limitations of the precious metal have triggered an intense research on a plethora of materials - both precious and non-precious.
To tackle the problem of high cost of platinum, several different approaches are being explored.
One way of reducing the cost is reducing the amount of platinum as a catalyst material. Another is maximizing the platinum usage by tailoring its properties towards optimum performance. Attempts have been made to produce platinum alloy catalysts, i.e. mixing platinum with other metals to reduce the precious metal content.
Several other materials with properties similar to platinum have been tried but they lack stability. One such metal is palladium which is also a precious metal but is abundant compared to platinum. Since palladium catalysts are not stable in electrochemical environments, extensive research has been carried out to stabilize it by producing alloy catalysts.
One of the major problems with palladium is the formation of an oxide layer on top of the palladium nanoparticles which severely hampers its catalyzing ability. In order to prevent oxide formation a number of transition metals like iron, cobalt, copper etc. have been alloyed with palladium. However, none of the alloy catalysts match the properties of platinum.
One promising alternative is core-shell catalysts with a monolayer of platinum as a shell on the non-platinum (palladium) or non-precious cores (copper). These use ultra-low quantities of platinum while retaining the same catalytic properties of Pt. This approach is limited to only small scale production of catalysts i.e. a few milligram scale synthesis and is yet to be implemented at the industrial scale.
The catalytic properties of platinum are highly shape dependant. At the IITB-Monash Research Academy in Mumbai, Research Scholar Naresh Nalajala has been working to exploit this very property. Working under the guidance of Manoj Neergat (IITB) and Prof. Bradley Ladewig (Monash University), Naresh has succeeded in producing shape-controlled nanoparticles of both precious and non-precious metals and then coating them with a thin layer of Platinum. The result is that the overall content of Pt is minimized without compromising on the catalytic properties.
"Since an impurity-free surface is mandatory for obtaining any electrochemical response from the catalyst, one of the aims of our research was to get rid of other reactants which adhere to the catalyst surface," says Naresh. "We have successfully developed a highly effective single-step method for cleaning the catalysts."
This new technology will help reduce the Platinum content in a fuel cell by 75%, making fuel cells cheaper and more economically viable. The team is excited at the prospect of their work facilitating the creation of a cheap and clean source of energy for the masses.
The IITB-Monash Research Academy is a Joint Venture between the IIT Bombay, India and Monash University, Australia. Opened in 2008, the Academy operates a graduate research program located in Mumbai that aims at enhancing research collaborations between Australia and India. Students study for a dually-badged PhD from both institutions, and spend time during their research in both India and Australia.
Research scholar: Naresh Nalajala, IITB-Monash Research Academy
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Supervisors: Prof. Manoj Neergat (IITB), Prof. Bradley Ladewig (Monash)
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