Our Faculty

• Assistant Professor, Department of Chemical and Engineering & Materials Science
• Assistant Professor, Center of Excellence in Advanced Materials & Green Technologies

• National merit scholarship 2002-2004
• ​DST Inspire faculty award 2014

RESEARCH THEMES

• Energy Materials
• Functional Materials

RESEARCH INTERESTS

My group’s primary research interest is in the development of materials for energy storage and conversion. We are interested in understanding the fundamental nature of the selected materials for applications such as hydrogen production & storage, and lithium-ion batteries.

Hydrogen Storage:

Hydrogen can be stored by various physical and chemical methods. Worldwide, many materials classes have been investigated concerning their potential to store hydrogen. However, each material class exhibits specific advantages along with disadvantages. Despite the search for a suitable high storage capacity materials that adapts to the standards set by the US-DOE for on-board mobile applications, there seems to be no significant breakthrough in that direction. It has been known that an ideal storage material should have (i) high gravimetric and volumetric capacity, (ii) cost-effective, (iii) no capacity degradation over thousands of cycles, (iv) made from materials that are earthabundant and eco-friendly, (vi) fast kinetics for charge and discharge requiring temperatures no more than 100 °C and ambient pressures. Presently, the only materials which are capable of storing and releasing hydrogen at ambient conditions are LaNi5, TiFe, and therefore they are under large-scale production. However, the gravimetric capacity of these compounds is low, i.e. these materials can store upto 1.2 wt.% and 1.5 wt.% of hydrogen, respectively. A promising class of materials with storage capacities of more than 6 wt.% is Mg-based alloys. Pure MgH2 can store 7.6 wt.% of hydrogen. However the rate of (de)hydrogenation is poor and compound is thermodynamically too stable. The equilibrium pressure is 1 bar at 300˚C. Mg-based systems can be modified to improve the sorption properties, such as temperature and reaction rate. It has been recognized that magnesium can be modified in different ways, e.g., by forming nano particles, alloying Mg with transition metals and adding catalysts. We are synthesizing and characterizing bulk Mg-TM alloys for hydrogen storage nickel and metal hydride battery applications.

Hydrogen Production:

Photo electrochemical (PEC) water splitting is considered as one of the ultimate solutions to make the hydrogen cycle sustainable as it requires only sunlight and water to generate hydrogen. The thermodynamic voltage for water splitting under standard conditions is 1.23 V and the photoactive materials must generate a photovoltage sufficiently high enough to drive water splitting reactions. Hematite is one of the most favorable materials for PEC water oxidation but they suffer from poor electronic conductivity, low absorption coefficient, short hole diffusion length and high electron-hole recombination rate. Altering the properties (both structural and dopant composition) of hematite nanostructures and forming heterojunctions by use of N-doped graphene and secondary metal oxides with a matching band gap would be a promising route to significantly improving the water splitting capability of α-Fe2O3. We are focusing a) developing highly active and durable graphene and hematite-based photo catalysts, b) determining the effects of synthesis routes on the PEC properties of catalysts, and c) developing a cost effective and environmental friendly photo electrode fabrication route for commercialization.

Lithium-ion batteries:

Graphene has elicited significant interest as anode material for Li-Ion energy storage applications due to its superior conductivity, high theoretical surface area (~ 2630 m2g-1), good mechanical properties, high flexibility, and ease of functionalization. Pre Lithiated-Graphite has been typically used as the anode material for Li-Ion batteries but it has poor kinetics for (de)insertion of lithium during charging and discharging and also a problem of volume expansivity during the same process. Also while the theoretical capacity of graphite is 372 mA.h g-1, the practical capacity is only ~320 mA.h g-1, hence, alternate anode materials are studied to improve the cycling capacity and storage capabilities. Metal oxides such as iron oxide, ruthenium oxide, nickel oxide, tin oxide, and manganese oxide have been studied as potential anode materials. Particularly, iron oxide seems to be more promising for practical applications because of its low cost, high theoretical specific capacity (1007 mAh.g-1), environmentally benign nature and easy handling. But one of the major issues of using iron oxide and in fact, most of the metal oxides, is volume expansivity and low electrical conductivity during high charge-discharge rates and hence, reduced cycle life. It has been shown that graphene/metal oxide nanocomposites exhibit improved electrochemical performance as result of reduced diffusion pathways for Li. Also, it is advantageous to consider nano-sized iron oxide because it can be easily prepared by electrochemical deposition at room temperature without any templates and catalysts. The need for a multilayered graphene-iron oxide structure is mainly due to its enhanced electrical conductivity, cycling durability and lithium storage performance. Also, using multi layered graphene could better accommodate the stresses induced due to the volumetric change during Li alloying/ de-alloying process because of its flexible structure. We aim at developing electrodeposited iron oxide-graphene nanostructures, including multilayer structures.

Electrochromism:

Conceptually, ‘electrochromism’ is the reversible optical change of specific compounds in response to a change in the oxidation state of the involved electro-active species. Metalhydrides expanded the classes of electrochromic materials and were listed among advanced optically switching inorganic compounds. Unlike most of the electrochromic color changing materials, metal hydrides even showed all three optical states (reflecting, absorbing and transmitting states) during the reversible (de)hydrogenation processes without any color change. metal-hydride switchable mirrors can be classified into three generations: rare earth (RE) metal hydrides, magnesium – rare earth (MgRE) metal hydrides and magnesium–transition metal (MgTM) hydrides. Various optical states have been identified during the (de)hydrogenation Mg-based alloys, which seem to be interesting for switchable mirror applications. According to Lambert-Beer’s law, the logarithm of the optical transmission is expected to be a good measure of the hydrogen concentration in a film. We aim at developing Mg based alloys thin films for switchable mirror applications.

KEYWORDS

• Hydrogen storage
• Hydrogen Production
• Metal hydrides
• Metal-oxides
• Electrochemistry
• Photoelectrochemical water splitting
• ​Electrochromic materials

COLLABORATORS

• Dr. M.V.V. Reddy, National University of Singapore, Singapore.
• Prof. B.V.R. Chowdari, Department of Physics, National University of Singapore, Singapore.
• Dr. Kaushik Jayasayee, SINTEF Materials and Chemistry, SINTEF, Norway.
• Dr. Murali Rangarajan, Center of Excellance in Advanced Materials and Green Technolgies, Amrita Vishwa Vidyapeetham, Coimbatore.

• Material Thermodynamics
• Advanced Electrochemistry
• Energy Storage Technologies