Carbon nanotubes as catalyst support in PEM Fuel cells

 

At IIT Madras, we study the performance of purified MWNTs as catalyst support for Polymer Electrolyte Membrane Fuel cells (PEMFC).PEMFC consists of a proton exchange electrolyte membrane sandwiched between an anode (negative electrode) and a cathode (positive electrode). Each of the electrodes is prepared by coating Pt/MWNTs electrocatalyst on one side of the carbon paper or cloth such that the maximum surface area of the Pt can be exposed to the hydrogen or oxygen. The large surface area of CNTs along with good electronic conductivity make them suitable material for supporting the catalysts in fuel cells. We prepare Pt/MWNTs electrocatalysts by different synthesis routes, use them as electrocatalysts for the oxygen reduction reaction in PEMFC and study the performance of PEMFC with respect to the catalyst synthesis and Pt loading.

Carbon nanotubes based Micro Fuel cells

 

In recent years, there has been a lot of interest on micro fuel cells as a next generation power source for portable electronics. The worldwide increase in portable electronic devices including laptop computers, mobile phones and other power packs have created a large and growing demand for energy sources that are compact, lightweight and powerful. Existing rechargeable battery technology, which has greatly developed, does not meet the needs of users.With more and more powerful devices, the current generation lithium ion rechargeable battery technology will struggle to meet ever-increasing power requirements. This creates an enormous opportunity for new power technologies and products.There is a need for developing better, long lasting solutions for mobile electronics devices.
In spite of this need, commercial fuel cell products based on traditional designs are yet to emerge in the market. While the potential and prospects for micro fuel cells are enormous, new approaches are required to overcome the technical and commercial challenges. Considerable efforts are being focused on the development of micro fuel cells that could potentially replace battery coin cells for micro applications. The main issue facing the portable fuel cell systems is to produce a compact, light weight system. In addition, the methodology of fuel supply needs to be developed. Presently we are involved in the development of carbon nanotubes based PEM micro fuel cells.

Carbon nanotubes based Supercapacitors


Supercapacitors are electrochemical capacitors with high capacitance and power density, which typically comprise of two electrodes separated by an insulating material that is ionically conducting in electrochemical devices. They store the electric energy in an electrochemical double layer formed at the solid electrolyte interface. Positive and negative charges from the electrolyte accumulate at the surface the electrodes and compensate for the electronic charges at the electrode surface. The resulting charge distribution iscalled electric double layeror electrochemical double layer (ECDL). The capacity of an electrochemical supercapacitor inversely depends on the separation between the charge on the electrode and the counter charge in the electrolyte. In order to achieve high capacitance, porous electrode materials with large accessible surface area are used.
Recently, there have been considerable attempts to use CNTs as electrode material for electrochemical energy storage systems. The CNTs are attractive materials for use as energy storage systems due to chemical and mechanical stability, low mass density and large surface area. At IIT Madras, we use purified MWNTs synthesized over alloy hydride catalysts as electrode material for supercapacitors. The performance of the supercapacitor test cell is being studied using cyclic voltammetry galvanostatic charge-discharge method and electrochemical impedence spectroscopy (EIS).

Development of Field Emission from Carbon Nano Materials

 

Electron sources play an essential role in information display. They mostly use the thermionic emission mechanism, where electrons are emitted from heated filaments ( hot cathodes ). Field emission is an alternative mechanism to extract electrons. It is a quantum effect where under a sufficiently high external electric field, electrons near the Fermi level can tunnel through the energy barrier  and escape to the vacuum level. A large field enhancement factor, high electrical conductivity and environmental stability are prerequisites for an efficient field emitter. For this reason, carbon nanotubes have been considered as one of the best field emitters due to their unique properties such as high aspect ratio, chemical inertness, high mechanical strength and high electrical conductivity. Several applications based on CNT emitters have been proposed in last few years including flat-panel displays, microwave tubes and lamps.
Presently, we are involved in the field emission studies of the different types of the carbon nanotubes (SWNTs, MWNTs and nanocoils) grown over varried types of substrates. Figures below  show  the  Field emission study setup which is to be housed in vacuum for measurements. The second figure shows the field emission from MWNTs.

 

Hybrid Carbon Nano Materials Based Solar Cell

Dye Sensitized Solar Cells (DSSC) and Organic Solar Cells are III solar cells and are believed to be cost effective alternatives for conventional silicon based solar cells. Research work at AENL is mainly focused at further improving the efficiency and reducing the costs of III G PV. Carbon based nanostructures like carbon nanotubes, graphene and their composites with nanoparticles of metals, metal oxides and polymers are synthesized. These materials are employed as active/counter electrode material in DSSC or as electron acceptors in organic solar cells and their performance is evaluated. The use of carbon nanostructures is expected to increase the surface area/porosity of the active layer, improve electron conduction in the active layer, and enhance the catalytic activity of the counter electrode in DSSC. In organic solar cells, the use of carbon nanostructures improves the electron separation and transport in the donor-acceptor blend (photoactive component).  

Carbon Nano Materials for EMI Shielding

In recent years electronics field has diversified in telecommunication systems, cellular phones, high speed communication systems, military devices, wireless devices etc. Due to the increase in use of high operating frequency and band width in electronic systems, there are concerns and more chances of deterioration of the radio wave environment known as electromagnetic interference (EMI). This EMI has adverse effects on electronic equipments such as false operation due to unwanted electromagnetic waves and leakage of information in wireless telecommunications. Recently, conductive polymer nano-composites have attracted a great deal of academic and industrial interest due to their potential applications in many areas including EMI shielding.
In contrast to larger conventional composite fillers, nano-composite fillers have at least one dimension in the nanometer range, including materials such as carbon nanotubes (CNT), graphite nanoplatelets (GNP) and graphene. These high-aspect ratio nano-scale fillers form interconnectivity conductive networks much more readily than conventional conductive fillers. Due to larger filler-matrix interface, mechanical and thermal properties may also be enhanced or improved. Furthermore, conductive polymer nano-composites are lighter and more easily processed.

Lithium-ion Batteries

 

Li-ion batteries applications vary widely from powering small devices to running hybrid electric vehicles and storing solar energy.  We are interested in studying battery materials (focusing mainly on anodes) that would meet the main desired goals of high-performance Li ion batteries. Our present studies include carbon based nanomaterials (Multiwalled carbon nanotubes and graphene) and their composites with different metal oxides and silicon as anode materials for Li-ion battery applications. The electrochemical performance tests include cyclic stability and galvanostatic charge/discharge profiles of half- as well as full-cells.

 

 

 

 

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