Ashish V. Pattekar & Mayuresh
V. Kothare talk with ScienceWatch.com and answer a few
questions about this month's Fast Moving Fronts paper in the
field of Engineering. The authors have also sent along images
of their work.
Article: A microreactor for hydrogen production in
micro fuel cell applications
Authors: Pattekar, AV;Kothare, MV
Journal: J MICROELECTROMECHANICAL SYST, 13 (1): 7-18 FEB
Addresses: Lehigh Univ, Integrated Microchem Syst Lab, Dept
Chem Engn, Bethlehem, PA 18015 USA.
Lehigh Univ, Integrated Microchem Syst Lab, Dept Chem Engn,
Bethlehem, PA 18015 USA.
Why do you think your paper is highly
This paper describes one of the earliest attempts to integrate an entire
chemical reactor on a silicon chip, namely, a miniaturized hydrogen
production chemical-plant-on-a-chip for micro fuel cell applications.
As rechargeable battery technology has matured in recent years, it seems to
be hitting a plateau in terms of improvements in energy storage capacity
and density. Miniaturized fuel cells have been considered as a possible
alternative power source for portable electronics and also as stationary
electricity generators/auxiliary power units (APUs)—with theoretical
energy storage densities up to 10 times those of current battery
However, a major challenge with portable fuel cells has been the difficulty
and hazards involved in the storage and handling of hydrogen, which is used
as the fuel for producing electricity.
Through the work described in this paper, we successfully demonstrated a
micro-reactor on a silicon chip that could chemically convert an easy to
carry and package liquid fuel, methanol, to hydrogen for the fuel cell on
an as-needed and on-demand basis—thus helping to close an important
gap in the realization of this next-generation portable power source.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
This paper describes a novel methodology for realizing a truly chip-scale
chemical reactor by synthesizing the knowledge of diverse concepts from the
fields of chemical, mechanical, and electrical engineering,
microelectromechanical system (MEMS) design and fabrication, and modeling
and implementation/optimization of microfluidic flows in silicon
microchannel networks using computational fluid dynamics (CFD).
"A view of the fabricated chip-scale methanol reforming
microreactor for micro fuel cell applications."
An important aspect of this work is the customized fluidic interconnects
and integrated on-chip heaters and temperature sensors that we developed
specifically for this project: to enable reliable fluidic connections to
our device and the ability to control the device operation without
increasing the overall footprint—a critical issue in portable
Also, we were able to optimize the design of our microfluidic channel
network by modeling and simulating the flow of the reacting fluids using a
computer—thus enabling us to further minimize the device footprint
without sacrificing throughput (hydrogen production rate).
These developments represent an important contribution to furthering
knowledge in the field of microreaction technology (MRT), specifically for
application to micro fuel cell systems.
Would you summarize the significance of your paper
in layman's terms?
Imagine a power source for your laptop computer that can last 8 to 10 times
as long as today's rechargeable batteries, without any increase in size and
weight. Or imagine reducing the weight of the batteries that a soldier has
to carry in the field today, from up to 40 pounds (yes—that's how
much the batteries weigh which need to be hauled around in order to power
the on-person electronics that today's soldiers carry!) to less than 5
pounds. This is the scale of the impact that miniaturized fuel cell systems
could have on portable power applications in the future.
Our paper addresses one of the key challenges associated with realizing
such a high-energy-density fuel cell-based power source: the problem of how
to supply the hydrogen needed for fueling a miniature fuel cell. Hydrogen
is extremely difficult to carry and store in pure form.
For example, even at an extremely high storage pressure of 10,000 psi, one
can only store about 0.04 gm of H2 per cubic centimeter (cc).
Even as liquid hydrogen, the density is only about 0.07 gm of H2
per cc—and these numbers don't include the added space and weight
requirements of the high-pressure cylinder or the cryogenic storage
Other approaches such as metal hydrides and carbon nanotube based
H2 storage have also been explored in the past, but without much
improvement in actual storage capacity. Compared to this, liquid
hydrocarbons such as methanol are pretty easy to store and handle, and for
each cc of methanol that is reformed in our microreactor we can produce
nearly 0.15 gm of hydrogen through the reforming reaction.
Of course, one needs to account for the fact that we need to supply steam
for the reforming reaction (which can actually come from the exhaust of the
fuel cell) and the additional volume of the hydrogen-generating
microreactor. Even with these considerations, however, a reformed hydrogen
fuel cell could provide an order-of-magnitude increase in energy storage
density over today's batteries—a very good improvement overall.
Our paper provides a very practical way of enabling such a reformed
hydrogen fuel cell based power source, and, more generally, demonstrates
how an entire chemical plant could be shrunk down to the size of a single
How did you become involved in this research and
were any particular problems encountered along the way?
This program began through a grant that Lehigh University received from the
US National Science Foundation through their solicitation titled
"Engineering Microsystems: XYZ-on-a-chip" in 1999. At that time,
miniaturization of a host of traditional engineering scale systems to a
"silicon chip scale" size was a rapidly emerging area of research.
As chemical engineers, we proposed the miniaturization of an entire
chemical plant to a chip-scale device and proposed to demonstrate this
concept through a micro-scale hydrogen generation chemical plant.
Some of the difficulties that we encountered were involved with the actual
fabrication of the devices on silicon and tuning the various semiconductor
processing/MEMS fabrication techniques to realize a fluidic microreactor
We were fortunate to be able to use the facilities at the Cornell
Nanofabrication Facility (CNF) at Cornell University to implement our
designs, and were provided lots of helpful advice on selecting the most
suitable techniques for making our test devices by the CNF staff.
Perhaps some of the greatest difficulties we encountered were in the area
of microfluidic interconnections, i.e., making reliable and leak-proof
fluid delivery ports for introducing and removing fluids from such a
microreactor system working at elevated temperatures and pressures.
When we found that state-of-the-art techniques for plumbing fluids to and
from these miniature devices would not satisfy our temperature and pressure
requirements, we ended up inventing our own designs for implementing such
"building blocks" for our microreactor system. This work has also been
published earlier, in a separate publication.
Where do you see your research leading in the
"This paper describes one of the earliest attempts to
integrate an entire chemical reactor on a silicon chip,
namely, a miniaturized hydrogen production
chemical-plant-on-a-chip for micro fuel cell
Since publishing the work referenced in this paper, we actually published
an improved design—building on many of the same concepts first
demonstrated here, but providing a 2X increase in throughput capacity and
an 18X to 20X improvement in performance in terms of pressure loss versus
production rate: thus moving this chip-based microreactor one step closer
to the intended micro fuel cell application.
This follow-up work was published in a paper titled "A radial microfluidic
fuel processor," (Pattekar AV; Kothare MV, Journal of Power
Sources147 [1-2]: 116-27, September 2005).
Regarding where our research might lead in the future, we are actively
seeking funding for further work in this area, to combine our microreactor
fuel reformer with a micro fuel cell and highly efficient, customized power
electronics to actually demonstrate a fully integrated
micro-fuel-cell-based power source with an order-of-magnitude improvement
in performance versus conventional batteries.
It is well known that micro fuel cells as alternative portable power
systems have generated a lot of interest, but have remained elusive thus
far due to various technical challenges. Several research groups, including
ours, are actively working on resolving these issues.
We certainly expect this work to eventually lead to the "power source of
the future"—one that lasts many times longer than today's batteries,
and enables a "truly wireless" world where portable devices do not have to
be plugged into a power outlet every so often.
One of us, Ashish V. Pattekar, is currently at PARC, which has an active
cleantech program. In a recent analysis, we have compared this approach to
that of the current recharging-discharging model of supplying portable
power using batteries.
It turns out that, on a per watt-hour basis, the overall cycle of
generating electricity in a coal-fired power plant and then converting to
low-voltage DC for recharging at the point-of-use results in almost twice
as much CO2 emissions overall, compared to the production and
use of methanol in a portable fuel cell as discussed in our
publication—leading to significant environmental benefits as well,
apart from the performance improvements over today's rechargeable battery
Do you foresee any social or political
implications for your research?
Perhaps the greatest societal implication of the work may be in reducing
our dependence on electric grid-based power for portable device charging
and instead using fully portable and decentralized autonomous power
Additionally, our preliminary calculations indicate that this technology,
if fully realized, could also reduce net greenhouse gas (CO2)
Another significant impact area of this work would be through a somewhat
scaled-up application as auxiliary power units (APUs) for large vehicles
such as transportation trucks and recreational vehicles (RVs) that
currently need to keep their engines running to supply electricity
requirements (e.g., refrigeration of perishables during transport, other
electrical equipment for use by personnel on the vehicle)—even while
the vehicle is parked.
After a typical 11-hour shift, truck drivers are required by federal law to
rest at least 10 hours. Idling trucks consume an estimated one gallon of
fuel each hour and emit carbon dioxide, nitrogen oxides (NOx), carbon
monoxide, particulate matter, and volatile organic compounds (VOCs).
Successful development of this technology for vehicle APUs would have a
significant impact on these idling vehicle emissions and related fuel
consumption by eliminating such inefficiencies as well.
Ashish V. Pattekar, Ph.D.
Member of Research Staff II
Palo Alto Research Center (PARC) Inc.
Palo Alto, CA, USA
Mayuresh V. Kothare, Ph.D.
R. L. McCann Professor
Department of Chemical Engineering
Center for Chemical Process Modeling and Control
Bethlehem, PA, USA