(393g) Interfacial Synergy Between Energy and Nanomaterials

 Introduction

Energy and Nanomaterials are intimately related.  Most energy processes occur at the
interface.  Nanomaterials, when
used as interfacial modifiers have the potential to significantly alter the
energy landscape.  Although carbon
nanomaterials have been explored for a suite of energy applications, to-date
the approach has been based on replacing bulk materials, not as interfacial
modifiers.  The work presented here
will highlight this latter approach by showing results for a suite of energy
applications from the author's own work.

 Experimental

Experimental details will be presented at the
presentation with regards to the synthesis and utilization of the
nanomaterials.  Our applications
include energy conversion, generation, storage, efficiency, conservation and
control.

 Results
and Discussion

Nanoscale materials are
redefining the relation between material composition, size and properties.  Chemical properties (e.g. reactivity)
and physical properties (e.g. surface area) become a strong function of size at
the nanoscale. 
Applications illustrated include the following selected examples from
the author's work: catalysis, composite materials, energy storage, sensors,
thermal management, and tribology.  The key concept is that the
nanomaterials serve as interfacial modifiers.  Since most energy related processes are dominated by
interfacial reactions, nanomaterials have the potential to dramatically affect
energy conversion rates and magnitudes. 
Examples follow.

Catalysis is central to particulate and NO_x
after-treatment systems.  A prime example of
reducing materials to nanoscale and realizing new
properties is catalysis by nanoscale gold.  Au nanoparticles
supported on oxides such as CeO₂, TiO₂ and Fe₂O₃
offer ambient temperature oxidation of CO, volatile organic compounds (VOCs) and potentially exhaust hydrocarbons.  Examples will be presented.

Lightweight
materials will reduce weight significantly yielding substantial benefits in
fuel efficiency with reduced emissions. 
Composites with substantial gains in Young's modulus, tensile strength,
and EM shielding may be realized in polymeric composites using carbon nanotubes
as an interfacial modifier rather than bulk filler [1].  As will be described, the interfacial
modification of a metal foil using carbon nanotubes directly grown upon the
foil.  The purpose of the foils is
to serve as a gas impermeable barrier layer within the polymer composite.

Advances
in energy storage include batteries, ultra-capacitors.  These can support lighting, appliances,
a starter, cooling fans, transmission and hydraulic systems, fuel and air
handling systems and ultimately enable hybrid systems.  Towards these goals, substantial gains
in Li ion battery cathode and anode materials have been realized using carbon nanofibers, coating processes and including elements such
as tin and silicon.  Modifications of the CNT surfaces
increases the Li ion capacity beyond
the theoretical limit of normal graphite. 
As an illustration, CNTs were directly
fabricated for this end-application use upon ultra-fine SS mesh.  Significantly no harvesting,
purification or processing (using binders) was required.  The CNTs
could be used directly as synthesized. 
TEM and SEM images will be presented of the CNTs
upon the SS mesh and discharge (de-intercalation) curves [2].

With regards to overall system integration and control, sensors
will play a prominent role [3]. 
With ultrahigh surface exposure relative to bulk material, nanoscale materials are exceedingly sensitive to gas
adsorption.  Exploitation of nanoscale properties will lead to new NO_x
sensors and in-cylinder oxygen sensors. 
Examples include catalyst coated metal oxide semiconductors capable of
ambient temperature operation, as will be illustrated in the talk.

Thermal management will benefit from nanofluids.  Nanofluids
can increase thermal conductivity and reduce radiator and heat exchanger
size.  Carbon-based nanofluids using nano-onions and
carbon nanotubes have increased water conductivity by ~ 20% [4].  Examples as shown by HRTEM images of
such nanocarbon additives will be compared during the presentation.

Lubrication is critical to many engine components and powertrain systems. 
Nanolubricants can bridge the gap between
fluid and solid materials [5].  As
additives with liquids or greases, synergistic properties may be realized,
particularly in boundary-phase lubrication.  Improved coating formulations and properties can reduce or
eliminate fretting and pitting. 
Results with nanocarbons show superior performance relative to graphite,
diamond like carbon (DLC) and even Teflon, as will be detailed.

 Conclusions

Nanoscale materials are redefining the relation
between material composition, size and properties.  Their applications to energy processes include selected
examples from the author's work. 
Selected technologies include catalysis, composite materials, energy
storage, sensors, thermal management, and tribology.  Interfacial modification serves to
affect changes in energy conversion rates, and transfer magnitudes.  This appears to be a rather universal
concept and suggests R&D directions for nano-engineering
of interfaces.

Acknowledgements

Funding through The
Penn State Institutes for Energy and the Environment (PSIEE) and the
Pennsylvania Keystone Innovation Starter Kit (KISK) is gratefully acknowledged.

References

 (1)     Vander
Wal, R. L., and Hall, L. J., Advanced Engineering Materials 2004, 6, 48-52.

(2)     
Luo, Y., Vander Wal,
R. L., and Scherson, D. A., Electrochemical and Solid
State Letters 2003, 6,
A56-A58.Vander Wal, R. L., Mozes, S. D., and Pushkarev, Nanotechnology 2009, 20,
105702-10.

(3)     
Hunter, G. W., Vander Wal, R. L., Liu, C. C., Xu, J. C., and Berger, G. M., Sensor and Actuators B 2009,
138, 113-119.

(4)     
Vander Wal, R. L., Mozes,
S. D., and Pushkarev, Nanotechnology 2009,
20, 105702-10.

(5)     
Street, K. W., Miyoshi, K., and Vander Wal, R.
L., "Application of Carbon Based Nano-particles to
Aeronautics and Space Lubrication", in Superlubricity,
Chapter 19, pp 311-340.  Edited by
Drs. Jean-Michel Martin and Ali Erdemir, Elsevier,
Amsterdam (2007).  (also NASA/TM-2007-214473).