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We combine experiments and simulations to study structure-property

performance correlation in nanofiber-based novel materials for energy

storage and conversion devices such as fuel cells, super-capacitors,

batteries and solar cells.

INTRODUCTION- NANOFIBERS

Proton exchange membrane fuel cell (PEMFC) converts the chemical energy

liberated during the reaction between hydrogen and oxygen to electrical energy.

Limitation of State-of-the-art Fuel Cells: High cost of platinum catalyst has

been one of the key challenges that has prevented the broad deployment of fuel

cells for transportation application

Objective: To study structure-property-performance correlation in nanofiber-based

fuel cell cathodes that maximize triple phase reaction surfaces and enhance

platinum utilization, thereby reducing cost.

NANOFIBERS FOR FUEL CELLS

Supercapacitors (or electrical double-layer capacitors)

are energy storage devices that store charge by

adsorbing ions on the surface of highly porous carbon

materials.

Carbon nanofibers with well-controlled, hierarchical pore

structure exhibiting specific surface area of 1500-2000

m2/g are ideal candidates for such devices.

NANOFIBERS FOR SUPERCAPACITORS

NANOFIBERS FOR BATTERIES Batteries are energy devices that convert chemical reaction energy to electrical energy

FUNDING AND CONTACT

Vibha Kalra

E-mail: vk99@drexel.edu

Ph: 215-895-2233

http://www.chemeng.drexel.edu/kalraresearchgroup/default.aspx

Nanofibers for Energy Storage and Conversion Laboratory

Group Members: Chau Tran, Qinsu Niu, Nataliia Mozhzukhina, Alda Kapllani, Alice Hu, Chris Curran

PI: Vibha Kalra

Nanofibers are fabricated via a process

called electrospinning that uses strong

electric field to accelerate and thin a

polymer solution/melt jet forming

nanoscale fibers

Why Nanofibers?

Nanofibers are 10-100 times smaller than those produced

from conventional mechanical spinning

High surface area leads to enhanced efficiencies in

energy devices

Interconnected porous structure with tunable porosity

enhances mass transport

Versatility of the electrospinning process

Electrospinning Set-up

SEM image of a typical nanofiber mat

Combining Multi-functionalities via Core-Shell Electrospinning

500 nm

Coaxial Nanofibers

Triaxial Nanofiber cross-section

200 nm

Schematic- Fabrication of Porous Carbon Nanofibers

Nanofibers of Carbon

Precursor/Sacrificial Polymer Blend

High temperature Calcination to

selectively remove sacrificial polymer

forming Porous Carbon Nanofibers

As-made Blend Nanofibers (Pre-Calcination)-SEM Images

Porous Carbon Nanofibers (Post-Calcination)-SEM Images

Longitudinal

section-TEM Image

-0.2

0

0.2

0.4

0.6

0.8

1

0 20 40 60

Vo

ltag

e (

V)

Time (s)

-4.E-3

-2.E-3

0.E+0

2.E-3

4.E-3

-1.0 -0.6 -0.2 0.2 0.6 1.0

Fabrication and Structural Characterization

Performance Characterization

Cross-section-

TEM Image

showing co-

continuous

carbon and

pore phase

50 nm

Cu

rre

nt

(Am

p)

Voltage (V)

174.43 F/g

Galvanostatic charge-discharge measurements Cyclic Voltammetry Measurements

50 nm

Lithium-air is a novel battery chemistry that utilizes

oxidation of pure lithium metal at the anode and reduction

of oxygen at the air-cathode to produce electricity

Cathode Reaction (discharge): 2Li+ + 2e-+ O2 Li2O2

They can theoretically provide 2 orders of magnitude

higher energy density than the state-of-the art Li-ion

batteries and therefore hold enormous potential for

all-electric vehicles.

Fabrication of nanostructured air cathodes that optimize transport of all

reactants (air, Li+ ions, and electrons) to the active catalyst surfaces and

provide enough spaces for solid lithium oxide products. Nanofibers with

tunable porosity and internal structure will serve as excellent cathodes.

200 nm

1 mm

SEM Micrograph of Manganese Oxide Nanofibers, potential catalyst for Li-air batteries

High Magnification Image showing MnOx Nanocrystals

within Nanofibers

XRD Data showing MnOx peaks

500 nm

Core-Shell Nanofibers with carbon core and

MnOx nanocrystal shell

Molecular Dynamics Simulation Snapshots showing formation of

lamellar domains under extensional flow

Critical Requirement for Successful Development of Li-air Batteries

Schematic of Ideal Multiphase boundary in Li-air cathode

TEM Image of microtomed nanofiber sections showing

co-continuous morphology of PAN (light region) and

Nafion (dark region)

Super-porous pure nafion nanofibers

with potential application in fuel cells

and as high sensitivity sensors

Nano-engineered materials with simultaneous proton and electron conductivity

Addition of polyacrylonitrile enhances extensional viscosity of Nafion to enable electrospinning

Pure Nafion

in DMF

Nafion /PAN

blend in DMF