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.