Science at the Edge
Engineering Seminar
September
30th,
2016
11:30
a.m.
Room1400
Biomedical
and Physical Sciences Building
Refreshments
served
at 11:15 a.m.
Professor Nathan. S. Lewis
California Institute of
Technology
Division of Chemistry
and Chemical Engineering
Beckman Institute and
Kavli Nanoscience Institute
Sunlight-Driven
Hydrogen
Formation by Membrane-Supported Photoelectrochemical Water
Splitting
Abstract
We are
developing an
artificial photosynthetic system that will utilize sunlight
and water as inputs
and will produce hydrogen and oxygen as outputs using a
modular, parallel
development approach in which the three distinct primary
components-the photoanode,
the photocathode, and the product-separating but
ion-conducting membrane-are
fabricated and optimized separately before assembly into a
water-splitting
system. The design principles incorporate two separate,
photosensitive
semiconductor/liquid junctions that will collectively generate
the 1.7-1.9 V at
open circuit to support both the oxidation of H2O
(or OH-)
and the reduction of H+ (or H2O). The
photoanode and
photocathode will consist of rod-like semiconductor
components, with attached
heterogeneous multi-electron transfer catalysts, needed to
drive the oxidation
or reduction reactions at low overpotentials.
The high aspect-ratio semiconductor rod electrode
architecture allows
for the use of low cost, earth abundant materials without
sacrificing energy
conversion efficiency due to orthogonalization of light
absorption and
charge-carrier collection. Additionally,
the
high surface-area design of the rod-based semiconductor array
electrode
inherently lowers the flux of charge carriers over the rod
array surface
relative to the projected geometric surface of the
photoelectrode, lowering the
photocurrent density at the solid/liquid junction and thereby
relaxing demands
on the activity (and cost) of any electrocatalysts. Flexible composite
polymer film will allow
for electron and ion conduction between the photoanode and
photocathode while
simultaneously preventing mixing of the gaseous products. Separate polymeric
materials will be used to
make electrical contact between the anode and cathode and also
provide
structural support. Interspersed
patches
of an ion conducting polymer will maintain charge balance
between the two
half-cells. The
modularity design
approach allows each piece to be independently modified,
tested, and improved,
as future advances in semiconductor, polymeric, and catalytic
materials are
made. This work will
demonstrate a
feasible and functional prototype and blueprint for an
artificial
photosynthetic system, composed of inexpensive, earth-abundant
materials while
simultaneously efficient, durable, manufacturably scalable,
and readily
upgradeable.
Bio
Dr. Nathan S. Lewis is the George L.
Argyros
Professor of Chemistry at the California Institute of
Technology. Professor
Lewis is Principal Investigator of
the Beckman Institute Molecular Materials Resource Center. His research interests
include artificial
photosynthesis and electronic noses. Nate continues to study
ways to harness
sunlight and generate chemical fuel by splitting water to
generate hydrogen. He
is developing the electronic nose, which consists of chemically
sensitive
conducting polymer film capable of detecting and quantifying a
broad variety of
analytes. Technical details focus on light-induced electron
transfer reactions,
both at surfaces and in transition metal complexes, surface
chemistry and
photochemistry of semiconductor/liquid interfaces, novel uses of
conducting
organic polymers and polymer/conductor composites, and
development of sensor
arrays that use pattern recognition algorithms to identify
odorants, mimicking
the mammalian olfaction process.
For further
information
please contact Prof. Richard Lunt, Department of Chemical
Engineering and
Materials Science at [log in to unmask]
Persons with disabilities have the right
to request and
receive reasonable accommodation. Please call the Department of
Chemical
Engineering and Materials Science at 355-5135 at least one day
prior to the
seminar; requests received after this date will be met when
possible.