AENL – Alternative Energy and Nanotechnology

Fuel Cell

Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cell (PEMFC) is one of the most promising candidates for the reliable and efficient conversion of chemical energy of the hydrogen fuel into electrical energy. It has drawn great interest due to its zero emission of pollutants, relatively low operating temperature, minimal corrosion problems, high efficiency and high power density for many applications including transport and electronic applications. Platinum (Pt) is the most effective electrocatalyst for sluggish oxygen reduction reaction (ORR) in PEMFC cathode, making them costly for commercial use. An active and stable cathode electrocatalyst promoting the ORR is desirable for better fuel cell performance with lower Pt content. Uniform decoration of platinum nanoparticles over conducting supports is one approach in that direction. Pt nanoparticles decorated partially exfoliated carbon nanotubes (Pt/PENT) were synthesized and employed as the cathode catalyst for PEMFC. It shows higher electrochemical active surface area, high mass and specific activity and power density outperforming the commercial Pt/C and other reported performance with hybrid structures of carbon nanotubes and graphene sheets; giving a maximum of 1 W cm power density with a total Pt loading of only 0.3 -2 mg cm on the electrodes.

Direct Methanol Fuel Cells

Direct methanol fuel cell (DMFC) is one of the promising candidates for solving the energy crisis in the future due to its high power density, compact design and easy refueling which makes it an appropriate candidate for portable applications. But the use of expensive catalyst, low reaction kinetics, methanol crossover and large over potential are the problems associated with the commercialization of DMFC. To reduce these problems some factors need to be taken care of apart from the catalytic activity like the morphology and structure of catalyst, to reduce catalyst content and enhance its utilization. Pt is the most active metal for dissociation of methanol but it gets poisoned due to adsorption of carbon monoxide, a byproduct formed during methanol oxidation. Hence bimetallic catalysts are widely used to regenerate inactive Pt sites.

Direct Ethanol Fuel Cells

Recently there has been an increasing interest on liquid fuels in fuel cells, which are easily transportable, and easily convertible into energy from the liquid state. Next to hydrogen, methanol is the favored fuel from the aspects of cost, efficiency, availability and existence in liquid form. However, the question of the toxicity of methanol remains crucial. Methanol is considered as a toxic product (mainly neurotoxic) and its large miscibility in water poses a major environmental problem. Compared with methanol, ethanol has advantages of lower toxicity, good stability, and low permeability across proton exchange membranes and higher energy density at room temperature than that of methanol. We are working on the development of novel carbon nanomaterials based catalyst support materials for DEFC.

Battery

Lithium Ion Battery

Lithium ion battery with high specific capacity is demanded for many applications. Conventional graphite anode could not fulfill this because of its -1low theoretical capacity of 372 mAh g . Our work evolves in designing the hybrid structures of carbon based nanomaterials in a much simpler and greener approach, compared to the existing hazardous, time consuming routes and employing them as anode material for LIB to understand the significant role played by individual elements and their physical and chemical properties. Partially exfoliated multiwalled carbon nanotubes (PENT) by unraveling few upper layers of parent multiwalled carbon nanotubes (MWNT) were -1 synthesized and investigated as anode material. It shows 880 mAh g capacity -at 100 mA gcurrent density and high rate capability by delivering a stable 157 -1 -1mAh g capacity at 10 A g . Enhanced performance of PENT can be attributed to the synergistic effect of the homogeneous distribution of the hybrid carbon nanostructure of 1D MWNT and 2D graphene nanoribbon (GNR) by providing high available surface area, electrical conductivity and defect sites, leading to improved Li intercalation with better transfer rate

Lithium sulfur battery

The development of high capacity energy storage systems is important due to the demand from portable electronic devices, power tools, and electric vehicles. Amongst the storage devices, lithium sulfur (Li-S) batteries have attracted great attention because the sulfur cathode has a high theoretical specific capacity of 1672 mA h g^-1 and an energy density of 2600 W h Kg^-1, which is three times higher than conventional cathodes. We are working on controlling the polysulfide shuttling using nanomaterials for enhancing the cyclic stability and specific capacity.

Lithium Air battery

Among beyond lithium ion battery chemistries, along with lithium sulfur batteries, Lithium air batteries are attractive for electric vehicle industry because of their extremely high theoretical capacity of 11680 Whkg^-1 which is ten times higher than the current lithium ion batteries (~100 Whkg^-1) and comparable to the energy density of gasoline (~ 13000 Whkg^-1). Lithium air batteries intend to use ambient oxygen in the environment for their operation. But, these batteries suffer from poor cyclability because of sluggishness of the oxygen reduction/evolution reaction, as well as the undesired side reactions occurring due to the other components of air such as moisture and CO₂. Also the present best performing electrocatalysts are not cost effective since they involve platinum group elements. We work on development of low cost bi-functional electrocatalysts and understanding the mechanism of reactions involved in Li-Air batteries, in order to improve the rechargeability of the battery.

Alternative cost-effective battery technologies

Sodium ion battery

To develop a cost-effective storage technology to the existing lithium ion battery, metal ion batteries like sodium ion, Magnesium ion, Calcium ion and aluminium ion batteries can be utilised due to its wide availability and cost effectiveness. We are working on sodium ion battery, room temperature sodium sulfur battery and aluminium ion battery.
In sodium ion battery, anode materials using carbon-based nanostructure like graphene and multiwalled carbon nanotubes has been developed. It involves the redesign of the carbon nanostructures for the better intercalation of larger size sodium ions. Also, working on the high voltage cathode materials for sodium ion battery. In addition, development of highly safe polymer electrolytes for sodium ion batteries are also developed

Sodium sulfur battery

The high energy density of sulfur is coupled with low cost sodium ion to develop a room temperature sodium sulfur battery. The formation and dissolution of sodium polysulfides into the electrolyte restricts its advantages to be utilized for practical applications. The work is focused on preventing the polysulfide dissolution using polar metal oxide-based compounds.

Aluminum ion battery

Aluminum is widely available in India and is highly safe to be handled in ambient conditions when compared to lithium and sodium metals. To intercalate the trivalent metal ions high voltage cathode materials, need to be developed. We are working on the development of high specific capacity cathode materials for aluminum ion battery. Development of high specific capacity cathode operating at higher voltage can pave the way for the development of rechargeable aluminium ion battery. A cathode structure with red phosphorous nanoparticles embedded in disordered carbon nanosheets from a cost effective resource by a simple and scalable technique is designed and developed. The developed cathode possess both high discharge voltage of 1.95 V and higher specific capacity of 350 mAh g^-1 at 30 mA g^-1 which is higher than graphite and other metal oxides.

Supercapacitors

Supercapacitors are similar to batteries; energy storage devices which possess high power density and long cycle life. Of late, hybrid supercapacitors mainly battery type hybrid supercapacitors (Lithium ion Capacitor, Aluminium Ion Capacitor and Sodium Ion Capacitor etc.), asymmetric type hybrid supercapacitors and hybrid nanocomposite-based supercapacitors are in trend. In our lab, we mainly focus on synthesis of different carbon-based nanomaterials such as carbon nanotubes (CNTs), hydrogen exfoliated graphene (HEG), electrospun carbon nanofibers, biomass derived activated carbon and their composites with metal oxides for application in different types of supercapacitors. We have achieved high specific value of 781 F g^-1 at 2 A g^-1 with long cycle life of 95.3 % over 10,000 cycles for symmetric solid state upercapacitor based on highly conductive, high-surface-area, heteroatom doped, porous carbon nanocomposite material.

Solar Cells

New-type solar cells typically including dye-sensitized solar cells (DSCs), organic solar cells (OSCs) and perovskite solar cells (PSCs) have been attractive reasonably for the low-temperature fabrications (below~150ºC), low thicknesses and unable colors. They potentially overcome Shockley-Queisser limit of 31-41% power efficiency for single bandgap solar cells. Electron transport layer (ETL) and hole transport layer (HTL) are introduced to reduce charge recombination in PSCs and OSCs, and electrolytes are required for harge transport and redox reaction in DSCs. Due to the advantages of abundance, long-term stability, good transparency, high conductivity and mechanical flexibility, carbon nanomaterials including fullerene, carbon nanotubes (CNTs) and graphene have been widely used for ealizing the flexibility and high performance of solar cells. GO and its derivatives exhibit high electron blocking capability and have been used as a qualified hole transport material. As a conductive electrode, carbon nanomaterials (like graphene, CNTs) are a promising substitute for commercial ITO leading to flexible solar cells. Graphene-based materials are also capable of functioning as charge selective and transport components in solar cell buffer layers. Moreover, low air stability and atmospheric degradation of the photovoltaic devices can be improved with graphene encapsulation due to its stable highly packed 2D structure.