Sweeping Action Of ZSM-5 In Fuel Cells Catalysis

Energy is a key component of economic development and growth and is an essential ingredient for a better lifestyle. Global demand for energy is swelling consistently and this is increasing the environmental pollution as power sectors depend primarily on the use of fossil fuels, especially in developing and underdeveloped nations.

To make the situation worse, fossil fuels beneath the earth crust are depleting alarmingly at a rate of 3% per annum. Hence there is an urgent search for an alternative fuel to fulfill the global energy demand.

Fuel cells are an option as they can generate electricity, cleanly and efficiently, by converting the chemical energy contained in a non-fossil fuel into electrical energy through a simple chemical reaction of positively charged hydrogen ions with oxygen or another oxidizing agent. The efficiency of fuel cells is higher than that of combustion engines as the former can generate electricity with efficiency around 60% and even higher with cogeneration while the efficiency of the latter is typically 33-35%.

Fuel cells can be a potential source of energy with less pollution in the atmosphere as recent research has found out ways to convert atmospheric carbon dioxide into ethanol by employing inexpensive copper nanomaterials with an exceptional high yield of around 63%. But platinum, which is considered a potent catalyst for electro-oxidation in fuel cells, has many demerits.

One primary concern is the scarcity and high cost of platinum and another is the in-situ coverage of the metal surface by carbonaceous by-products reducing the active sites available to catalyze fuel cell reactions. ZSM-5, a common zeolite, can be a solution to the two main problems of use of platinum.

Platinum nanoparticles supported by zeolites as co-catalyst are found to be better electro-catalysts. Silica in zeolite framework and modification of the electronic configuration of platinum increases the electrocatalytic efficiency. The lower density of valence electron in zeolite modified electrodes than that of pure platinum resulted in a lesser concentration of adsorbed carbonaceous and higher electrocatalytic efficiency.

Silica and alumina in ZSM-5 can facilitate cleansing of the catalytic electrode surface because, in case of zeolite modified electrodes, the oxygen-containing species in the framework strongly react with adsorbed carbon monoxide on the platinum surface to release active sites for further catalysis. The sweeping action of ZSM-5 is shown in the image below.

The mechanism of electro-oxidation reaction over zeolite modified electrodes is initiated by the flow of reactant molecules towards the electrode surface and resultant adsorption. Then the adsorbed intermediate gives product molecules that desorb from the electrode surface.

The zeolite modified electrode surface acts as a table tennis board where the reactants convert to products dropping in and popping out as ping pong ball as shown in the image at the beginning.

These findings are described in the article entitled Electro-oxidation of Methanol and Ethanol Catalyzed by Pt/ZSM-5/C, published in the journal Electroanalysis. This work was led by Basu Maan Daas and Susanta Ghosh from Netaji Subhash Mahavidyalaya, Udaipur, Tripura, India and the Integrated Science Education & Research Centre, respectively.

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