ELECTROOXIDATION STUDY OF ACETIC ACID IN MEMBRANELESS MICROFLUIDIC FUEL CELLNAME:- PROJECT MENTOR:-SHASHANK PARDHIKAR DR. H.L. PRAMANIK14045085SOLANKE PAWANKUMAR14045097

DIH SUMMER PROJECT EVALUATION

BACKGROUND Since energy is still mainly based on

fossil fuels, increasing energy demands have led to their depletion and to significant environment implications.

Fuel cells are useful tool to reduce carbon emission.

Fuel cells are efficient, environment friendly.

PRINCIPLE OF FUEL CELL Fuel cells are galvanic cells in which

free energy of a chemical reaction is converted into electrical energy.

∆rG= – nFE(cell) E(cell) = E(cathode) – E(anode)

TYPES OF FUEL CELLPolymer Electrolyte Membrane Fuel CellDirect Alcohol Fuel CellPhosphoric Acid Fuel CellAlkaline Fuel CellSolid Oxide Fuel CellMolten Carbonate Fuel CellMicrofluidic Fuel Cell

MICROFLUIDIC

FUEL CELL

WHAT IS MICROFLUIDIC CELL?

It can be defined as a fuel cell with fluid delivery and removal, reaction sites and electrode structures all confined to a microfluidic channel.

Microfluidic cells typically operate in a co-laminar flow configuration without a physical barrier, such as a membrane to separate cathode and anode.

HOW MICROFLUIDIC CELL WORKS? Streams of oxidant and fuel flow

laminarly in a Y-shaped microchannel.

Examples of Fuel – Formic Acid, Ethanol, Methanol, Acetic Acid etc.

Examples of oxidant – Hydrogen Peroxide, Potassium Permanganate etc

Electrolyte is added to fuel and oxidant to provide ionic charge transfer between electrodes.

WHY ELECTROLYTE IS BEING ADDED TO MICROFLUIDIC CELL?

To enhance ionic conduction To decrease ohmic losses

Generally strong acid or strong base is used as electrolyte.

Precaution- Large concentration of electrolyte should be avoided because it can corrode the cell.

Examples – Suphuric Acid, Potassium Hydroxide

TYPES OF MICROFLUIDIC CELL CONFIGURATION-

Y shaped configuration T shaped configuration F shaped configuration

ADVANTAGES OF MICROFLUIDIC CELL

As it does not contain membrane, all membrane related issues were eliminated like membrane degradation, water management, fuel crossover etc.

It allows the cell to operate in acidic and alkaline medium.

Size is less.

APPLICATIONS OF MICROFLUIDIC CELL

In near future, microfluidic cells are most likely to replace batteries of low power application such as mobiles, laptops etc.

It can be used in DNA analysis devices, blood diagonastics, pH gradient for use in iso-electronic focussing, glucose sensors, microfluidic circuit boards, etc.

LITERATURE REVIEW-Authors

Reactants Electrolyte Cell PerformanceCurrent density (mA/cm2)

Power density (mW/cm2)

Li et al Formic Acid(0.5M)Dissolved O2

Sulphuric Acid (0.1M)

1.5 0.18

Chobanet al

Formic Acid(2.1M)Dissolved O2

Sulphuric Acid(0.5M)

0.8 0.17

Choban et al

Methanol(1M)Dissolved O2

Sulphuric Acid (0.5M)

8 2.8

Salloum et al

Formic Acid(0.04M)KMnO4(0.01M)

Sulphuric Acid(0.5-1M)

5 2.8

Chobanet al

Methanol(1M)Dissolved O2

Sulphuric Acid or Potassium Hydroxide(1M)

40 12

OBJECTIVE- To fabricate the electrodes of the cell. To study the performance of

microfluidic fuel cell on different concentration of fuel i.e. Acetic acid.

To study the performance of microfluidic fuel cell on different concentration of electrolyte.

MATERIALS USED- PMMA Sheets Carbon paper Pt tin catalyst PTFE solution Nafion Epoxy adhesive Teflon tape Copper foil Acetic acid Hydrogen peroxide Sulphuric acid

FABRICATION OF ELECTRODES-The anode was prepared from Pt-tin/C electrode catalysts, activated carbon and mixture of Nafion ionomer (SE-5112, DuPont) and PTFE dispersion, which acted as binder. The anode electrode-catalysts slurry was prepared by dispersing the required quantity of electode-catalysts powder in Nafion solution with few drops of PTFE dispersion for 30 min using an ultrasonic water bath to obtain electrode catalyst slurry. The slurry was painted on a carbon diffusion layer using a paintbrush uniformly in the form of continuous wet film. Then it was dried in an oven for 1 hour at a temperature of 80oC. The cathode was prepared using similar compositions with Pt-black high surface areas electrode catalyst. The dried anode and cathode were sintered at a temperature of 300oC in a hot oven. The sintered electrodes were placed on the sides of grooved microchannel.

EXPERIMENTAL SETUP AND METHOD-

Fuel cell consisting of Y-shaped microchannel with electrodes on the inner sidewalls of the main channel. The cell was held together between two PMMA sheets using a set of retaining bolts positioned around the periphery of the cell. PTFE sheet were used for isolation and leakage prevention. The acetic acid concentration of 1M, 1.5M and 2M was fed at anode at different flow rate using a peristaltic pump. Hydrogen Peroxide is used as oxidant. For different concentration of acetic acid and electrolyte, the current and voltage were recorded using multimeters at variable electronic load.

RESULT AND DISCUSSION:-EFFECT OF FUEL CONCENTRATION ON CELL PERFORMANCE-

Cell performance improves with increasing fuel concentration from 1.0 M to 1.5 M and declines at higher concentration. The anode potential shows decreased oxidation kinetics at the acetic acid concentration of 1.0 M mainly due to dilute reactant on anode surface. At the higher concentration (2.0 M) of acetic acid cell performance is decreased due to fuel crossover to cathode.

EFFECT OF ELECTROLYTE-

The peak power density increases on increasing the electrolyte concentration from 0.1 M to 0.2 M mainly due to improved conduction and reduced internal resistance. However, the cell performance declines when electrolyte concentration is increased to 0.3 M sulphuric acid. This phenomenon can be attributed to the reduced acetic acid electro-oxidation due to enhanced blockage of sulphate and bisulphate on catalyst active sites at higher electrolyte concentration

EFFECT OF FLOW RATE-

For high Peclet-number flow regimes inter-diffusive broadening decreases near the top and bottom walls.

Diffusive broadening is the main cause of reactant crossover.

Reduction in the concentrations of fuel/oxidant streams leading to decreased current density.

Fuel crossover to cathode side leading to degradation of open-circuit potential. Since platinum is usually used for oxygen reduction at the cathode side, crossover fuel oxidation over Pt can block the catalytic active sites decreasing the rate of electroreduction of oxygen at the cathode.

EFFECT OF OXIDANT CONCENTRATION-

After increasing the concentration of Hydrogen Peroxide from 1M to 2M, open circuit voltage increases due to increase in oxygen concentration but after increasing the concentration further open circuit voltage reduced because more Oxygen bubbles were produced and Oxygen gas bubbles produced at the fuel cell cathode introduced an unsteady two-phase flow component which resulted in perturbed co-laminar flow and reduced fuel cell performance.

CONCLUSION- In this study microfluidic fuel cell was tested at

different fuel and electrolyte concentration. Maximum power density and current density was obtained at 1.5 M acetic acid concentration and 0.2 M sulphuric acid concentration. There is increase in OCV as we increase the flow rate. There is a big potential for research in this field and new advances can be explored in coming years. High performance can be achieved by paying careful attention in design considerations in view of the coupled mass transport to reactive sites and the electrochemical kinetics. Ohmic losses should be decreased by optimizing the spacing between electrodes and enhancing the conductivity of electrodes and aqueous electrolytes.

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N.T. Nguyen, S.T. Wereley, Fundamentals and Applications of Microfluidics, Artech House, Boston, MA, 2002.

Choban ER, Waszczuk P, Kenis PJA. Characterization of limiting factors in laminar flow-based membraneless microfuel cells. Electrochemical and Solid-State Letters 2005; 8(7):A348e52.

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