pnas201118655 15..17


Profile of Daniel G. Nocera

I
n a dim-lit laboratory in the chemistry
department at the Massachusetts In-
stitute of Technology, a postdoctoral
researcher points out the parts of

a handmade device that might be our
best hope yet for harnessing solar
energy. A chip the size of a microscopy
slide, the device is an artificial leaf, the first
of its kind made of relatively abundant and
inexpensive materials that, if further
refined, might help make the sun our main
source of energy. The brainchild of
National Academy of Sciences member
and MIT chemistry professor Daniel
Nocera, the leaf’s stainless steel chip is
coated with silicon, which can harvest
sunlight, and catalysts that can use that
light to split water into hydrogen and ox-
ygen. When burned in a fuel cell, Nocera’s
postdoctoratal fellow Joep Pijpers ex-
plains, hydrogen generates electricity and
water. The catalysts can help produce
enough hydrogen from a liter of water
to power an average home in the de-
veloping world. Someday, Nocera
hopes, this technology might help person-
alize energy in the Western world, un-
tethering its people from power grids
based on energy sources that emit planet-
warming gases.
Although he was born in Boston and

returned to the city later in life, Nocera
spent a childhood split between four states,
as he moved with his father, who worked in
retail sales. That peripatetic childhood
came with a price. “When you move that
much, you don’t easily make friends. I
became afraid to become attached to
people,” he says. The anxiety of separation
spurred his interest in science as a place of
refuge. Armed with an amateur micro-
scope built from an educational kit,
Nocera stoked his scientific curiosity,
examining creatures unearthed from his
back yard. “Science seemed like an in-
dividual’s pursuit, something I could carry
with me no matter where we moved,” he
recalls. Nocera soaked up the funda-
mentals of science at Bergenfield High
School in New Jersey, motivated by phys-
ics and chemistry teachers. In 1974, he
enrolled for a bachelor’s degree in chem-
istry at Rutgers University, New Jersey,
where as a plucky freshman, he vol-
unteered to perform experiments with
chemist Lester Morss, who studied lan-
thanides and actinides—periodic table
residents that include radioactive and
rare earth elements. For his under-
graduate thesis under the guidance of
Rutgers chemist Joseph Potenza, Nocera
helped illuminate a physical phenomenon
called dynamic nuclear polarization,
which affects subatomic interactions be-
tween electrons and nuclei. Analyzing

those interactions can help researchers
determine high-resolution structures
of biologically important molecules
through methods such as NMR
spectroscopy.
In 1979, Nocera began doctoral studies in

inorganic chemistry in the laboratory of
Caltech chemist Harry Gray. There, to-
gether with Caltech chemist Jay Winkler,
Nocerafashionedalaser-basedtechniqueto
measure the movement of an individual
electronthrough proteins, a pursuit that had
preoccupied Gray for nearly a decade and
that could help unravel natural reactions
like photosynthesis. Those findings, collec-
tively called fixed-distance electron transfer,
led to well-regarded reports in the Journal
of the American Chemical Society (1, 2)
and formed the basis of Nocera’s then-
novel interest in using light to generate
energy. But it was his 1986 paper, which
reported the observation of a chemically
reactive intermediate named the delta star
in reactions of quadruple-bonded metals,
that Nocera remembers best. Although the
report was published in the Journal of the
American Chemical Society (3), the research
also found an unlikely outlet; the delta
star became a centerpiece of a bestselling
work of detective fiction by the American
writer Joseph Wambaugh (4) in which a
band of chemistry professors help solve
a mysterious murder. “The writer actually
featured the abstract of the paper in the
novel,” Nocera recalls.

Trafficking Electrons and Protons
In 1983, just before graduation, Nocera
accepted an offer of assistant professor-
ship from Michigan State University
in East Lansing, Michigan. There, he
focused on the so-called energy problem,
a cause that he has championed for most
of his scientific career. Nocera brought
his electron transfer expertise gained in
Gray’s laboratory to bear on the thorny
problem of multiple electron transfer. At
the heart of plants’ ability to use sunlight
for photosynthesis is their near-mystical
knack for performing chemical reactions
that involve the transfer of multiple
electrons. Sunlight triggers the formation
of excited electronic states in plant cells
that, through a cascade of steps, lead to
the coupling of protons and electrons,
ultimately producing hydrogen and
oxygen. It is a testament to the fiendish
difficulty of replicating this chemical
reaction—which plants carry out with
casual ease—that a century after Italian
chemist Giacomo Ciamician wrote in
Science that “the photochemical pro-
cesses that hitherto have been the
guarded secret of the plants . . . will
have been mastered by human in-
dustry,” researchers are still trying to
perfect artificial photosynthesis (5).
Long considered a hurdle to harnessing

sunlight, the field of multielectron chem-
istry presented problems that Nocera
addressed through kinetic studies using
lasers. Among the first chemical reactions
he addressed was the transfer of two
electrons to an atom of hydrogen, a re-
action catalyzed by hydrogenase enzymes,
which help orchestrate anaerobic metab-
olism in organisms like algae. Under-
standing how algae carry out the reaction,
for example, could help researchers gen-
erate hydrogen for use as a fuel. More
importantly, multielectron chemistry
turned out to be a gateway to a more
complicated reaction called proton-cou-
pled electron transfer (PCET), whose
unraveling earned Nocera membership
in the National Academy of Sciences
years later. PCET pointed to a way to
harness sunlight.
Such limber explorations of subatomic

chemistry led to an assistant professorship
in 1997 at MIT, where Nocera set
about unifying the phenomena of multi-
electron chemistry and PCET as a path
toward addressing the energy problem.
Through nifty calculations that accounted
for worldwide population, average gross

Daniel G. Nocera.

This is a Profile of a recently elected member of the Na-
tional Academy of Sciences to accompany the member’s
Inaugural Article on page 10337 in issue 23 of volume 107.

www.pnas.org/cgi/doi/10.1073/pnas.1118655109 PNAS | January 3, 2012 | vol. 109 | no. 1 | 15–17

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domestic product per capita (a measure of
productivity), and energy consumed per
unit of gross domestic product (a measure
of energy conserved while achieving that
productivity), Nocera estimated in a
2006 PNAS Perspective that, by the turn
of the century, the global demand for
energy would hover around a staggering
43 trillion watts (6). Although fossil fuels,
like coal, oil, and natural gas, can to-
gether meet that demand handily, their
use is forever pinned with an asterisk:
climate change caused by the emission of
greenhouse gases. Achieving the emis-
sions reduction goals set by the In-
tergovernmental Panel on Climate
Change, then, would call for a reliable
source of carbon-neutral energy.

High Noon for Solar Energy
Nocera turned to an unfailing source: A
benchmark for reliability, the sun provides
more energy in an hour than people typi-
cally consume in a year. And there are two
main ways to harness that energy, namely
producing steam by using turbines or
converting sunlight into electricity by using
photovoltaic panels. But the challenge in
harnessing solar energy lies in the ability to
storethecapturedenergyforuseatnightor
when the sun is blanketed by clouds. A few
ways to store solar energy at night have
been developed, like entrapping the excess

energy in molten salt or compressed air.
But none are cost-effective enough to
render solar energy an industrial option.
In seeking a practicable solution to this
seeming impasse,Nocera lookedtonature.
His unraveling of multielectron chemistry
and PCET led to a quest to mimic pho-
tosynthesis. To that end, he sought an in-
expensive catalyst that could use sunlight
to split water into hydrogen and oxygen.
The gases could then be combined in a fuel
cell to generate electricity and water, thus
creating a potentially bottomless, self-
sufficient powerhouse. “Photosynthesis is
a water-splitting reaction and involves
four electrons and four protons. Plants
store and move four electrons from water
and produce an electric current. They also
convert the electric current into chemical
current conducted by protons, which
are moved as atoms. Atoms are heavier
and tougher to move than electrons. What
we needed was a catalyst that could
move atoms and assemble them,” Nocera
explains.
By 2002, Nocera had developed a rho-

dium-based catalyst to generate hydrogen
gas from a chemical solution using light
energy to make hydrogen atoms from
protons and electrons wrested from the
solvent. Meanwhile, other researchers at
the US National Renewable Energy
Laboratory in Golden, Colorado, had
uncovered ways to use semiconductors
to split water. But rhodium and semi-
conductors are too expensive for large-
scale use. Also, there was still no
reasonable means to generate oxygen
from water. “Reading the book of nature
helped us move closer to an inexpensive
catalyst for oxygen,” Nocera says. A re-
vealing chapter in the book came to light
when London’s Imperial College bio-
chemist James Barber published the high-
resolution crystal structure of the enzy-
matic machinery that helps plants carry
out photosynthesis. Known as the oxygen-
evolving complex, this macromolecular
structure was found to be the secret
behind plants’ photosynthetic prowess.
“When we saw what the plant’s catalytic
machinery looked like, we set out to
design a synthetic catalyst to split water,”
he adds. Thanks to a National Science
Foundation grant to explore renewable
energy sources and a private, philan-
thropic gift, Nocera set up an energy
research program at MIT called the Solar
Revolution Project, one of whose goals
was to develop such a catalyst.
Bolstered by the influx of research dol-

lars, Nocera and his then-postdoctoral
fellow Matthew Kanan fashioned a process
that could produce hydrogen and oxygen
from water. The process involves an elec-
trode made of indium tin oxide, which
when subjected to a voltage in a catalytic
solution of cobalt, potassium phosphate,

and water, generates oxygen gas and
hydrogen ions. At a different electrode
coated with a platinum catalyst, the hy-
drogen ions recombine into hydrogen gas.
As the reaction proceeds, the cobalt cat-
alyst breaks down—but reassembles over
time, regenerating itself for prolonged
use. Published in a 2008 Science report,
Nocera’s process was hailed as a break-
through (7). Over the course of a day, the
catalyst could use electricity generated
by a photovoltaic panel to split water
and produce energy to power an average
American home. The strength of the cat-
alyst, Nocera explains, was in its ability for
near-continuous self-repair, not to men-
tion the relative safety, abundance, and
affordability of raw materials such as co-
balt and phosphate. “The real scientific
discovery was its self-healing property,
which resembles that of the oxygen-
evolving catalyst of photosynthesis,” No-
cera says. Yet Nocera’s catalyst had
a number of shortcomings that needed to
be addressed. First, the catalyst needed
a good deal of electricity to start splitting
water, affecting its overall efficiency.
Complicating the matter further, it could
only accept low levels of current. Further
still, the platinum used to generate hy-
drogen was prohibitively expensive for
Nocera’s purpose. In the next two years,
Nocera and his team surmounted some
of those problems, publishing in a 2010
PNAS inaugural article, an improved ox-
ygen-evolving catalyst based on nickel
borate (8). At a pH of 9.2, thin films of the
catalyst, the paper reported, could be
electrodeposited from dilute solutions
of nickel borate electrolyte, allowing re-
searchers to control the thickness of the
films and the electric potential at which
the catalyst operates. “Structurally, the
nickel–borate catalyst is similar to the
cobalt catalyst, but it runs faster and
better in certain pH regimes. It also
shows that our original discovery isn’t
an isolated curiosity,” Nocera says. “Our
focus is now on this nickel–borate cata-
lyst,” he adds.

No Mere Pie in the Sky
To help commercialize the water-splitting
catalyst, Nocera cofounded Sun Catalytix,
a Massachusetts-based technology firm
that hopes to put his basic research
advances to work for people. The com-
pany’s long term goal is to personalize
energy by producing it at its point of use
instead of relying on traditional methods
of distribution along grids from a central-
ized source. In a tidily imagined scenario,
Nocera envisions turning surplus light
energy harvested by rooftop photovoltaic
panels into electricity with the help of his
water splitter, a pair of underground
tanks to store hydrogen and oxygen, and
a fuel cell to burn the hydrogen. “Thus,

An artificial leaf.

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your home becomes its own solar power
station,” Nocera explains with his char-
acteristic can-do spirit. In September
2009, National Geographic featured a
snapshot of Nocera cradling little more
than a gallon of water in his hands—the
amount that he estimates is needed to
power an average American home. A
vision of pharaonic scope that Nocera
hopes to someday pull off, personalized
energy must first overcome several hur-
dles, not least of which are the still-
prohibitive cost of fuel cells and the po-
litical inertia facing alternative energy.
“Over the years, we’ve been getting
greener in thinking about the future of
our energy, but it’s still largely carbon-
based. The slow pace of greening is
disappointing, mainly because of the
lack of policies to implement carbon
pricing,” he says.
Intertwined with this vision to wean the

Western world from its dependence on
fossil fuels is Nocera’s goal to make solar
energy a predominant resource in de-
veloping countries, which remain rela-
tively independent from large power
grids. But most photovoltaic panels are
made of semiconductors like silicon,
whose high cost would rapidly scupper
plans to commercialize personalized en-
ergy in poor countries. Which is why

Nocera developed a workaround by
further improving his water-splitting
catalyst.
“There’s a lot of cost going into the

fabrication of the photovoltaic panel. If I
could show there was a way to integrate
the silicon directly on the catalyst, I
wouldn’t need a panel,” he says. That is
precisely what he showed to a room full of
scientists and engineers at a March 2011
meeting of the American Chemical Soci-
ety in Anaheim, California. The demon-
stration doubled as a preview to a 2011
PNAS paper describing his version of an
artificial leaf (9). Based on the oxygen-
evolving complex of leaves, Nocera’s de-
vice is composed of a slender film the size
of a business card that bears crystalline
silicon cells covered with a layer of in-
dium tin oxide and containing his cata-
lysts. As sunlight hits a beaker of water
into which the leaf is immersed, oxygen
and hydrogen bubble up from separate
sides of the leaf. By directly placing his
catalysts on the silicon, Nocera obviated
the need for a photovoltaic panel. “This is
really what I started out to do in Gray’s
lab—to make an unsupported device that
could split water with nothing else but
sunlight,” Nocera says. In laboratory set-
tings, Nocera showed, the artificial leaf
worked continuously for three days. No-

cera has struck a partnership with Indian
businessman Ratan Tata to help harness
solar energy in parts of rural India, and
he hopes that a prototype artificial leaf
might be ready for use in people’s homes
within a few years.
Nocera’s efforts to harness solar energy

earned him a place in Time magazine’s
2009 list of the 100 most influential
people, an honor that he shared with US
Secretary of Energy Steven Chu. “The
recognition was noteworthy, because we
were among the few scientists who made
the list that year,” Nocera recalls. His
commitment to solving the energy crisis
runs beyond the often-closeted world of
academia. To help demystify scientific
efforts to use solar energy to solve the
energy crisis, Nocera has partnered with
the MIT Museum and the Boston Mu-
seum of Science, mounting exhibits that
have enthralled visitors. “People often
think that cool discoveries are made by
technocrats. What they don’t get is that
they are enabled by basic science,”
Nocera says. “My goal is to help people
see the road between basic science at
places like MIT and technology in the
real world.”

Prashant Nair, Science Writer

1. Winkler JR, Nocera DG, Yocom KM, Bordignon E,
Gray HB (1982) Electron-transfer kinetics of pentaam-
mineruthenium(III)(histidine-33)-ferricytochrome c. Mea-
surement of the rate of intramolecular electron transfer
between redox centers separated by 15 Å in a protein.
J Am Chem Soc 104:5798–5800.

2. Nocera DG, Winkler JR, Yocom KM, Bordignon E, Gray HB
(1984) Kinetics of intermolecular and intramolecular
electron transfer from ruthenium (II) complexes to ferri-
cytochrome c. J Am Chem Soc 106:5145–5150.

3. Nocera DG, Gray HB (1981) Electron transfer chemistry
of the luminescent excited state of octachlorodirhenate
(III). J Am Chem Soc 103:7349–7350.

4. Wambaugh J (1983) The Delta Star (Bantam Publishers,
New York).

5. Ciamician G (1912) The photochemistry of the future.
Science 36:385–394.

6. Lewis NS, Nocera DG (2006) Powering the planet:
Chemical challenges in solar energy utilization. Proc
Natl Acad Sci USA 103:15729–15735.

7. Kanan MW, Nocera DG (2008) In situ formation of an
oxygen-evolving catalyst in neutral water containing
phosphate and Co2+. Science 321:1072–1075.

8. Dincă M, Surendranath Y, Nocera DG (2010) Nickel-bo-
rate oxygen-evolving catalyst that functions under be-
nign conditions. Proc Natl Acad Sci USA 107:10337–10341.

9. Pijpers JJ, Winkler MT, Surendranath Y, Buonassisi T,
Nocera DG (2011) Light-induced water oxidation at silicon
electrodes functionalized with a cobalt oxygen-evolving
catalyst. Proc Natl Acad Sci USA 108:10056–10061.

Nair PNAS | January 3, 2012 | vol. 109 | no. 1 | 17

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