Production of Hydrogen Using
Nanocrystalline Protein-Templated
Catalysts on M13 Phage
Brian Neltner,
†
Brian Peddie,
†
Alex Xu,
†
William Doenlen,
†
Keith Durand,
‡
Dong Soo Yun,
†
Scott Speakman,
†
Andrew Peterson,
§
and Angela Belcher
†,,
*
†
Department of Materials Science and Engineering,
‡
Department of Mechanical Engineering,
§
Department of Chemical Engineering, and
Department of Biological
Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
H
ydrogen fuel cells generate power
by chemically converting hydro-
gen and oxygen into water. This
process does not produce power through
the use of a heat engine, so the maximum
efficiency can be quite high.
1
Although hy-
drogen has a mass energy density of 141.8
MJ/kg, the volumetric energy density is only
0.0116 MJ/L for uncompressed hydrogen
and only 11.4 MJ/L for hydrogen com-
pressed to 100 MPa (not including the
weight and volume of the tank required to
maintain such a high pressure). By compari-
son, ethanol has an energy density of 29.7
MJ/kg but has a volumetric energy density
of 23.4 MJ/L at atmospheric pressure.
2
By
catalytically reforming ethanol into hydro-
gen gas, the benefits of having a high en-
ergy density fuel can be combined with the
benefits of using hydrogen fuel cells to per-
form work more efficiently, resulting in a
significantly more practical way to incorpo-
rate fuel cells into existing systems.
The catalytic oxidative steam reforming
of ethanol-water mixtures saw a major
breakthrough in 2004, when the complete
conversion of ethanol over rhodium-ceria
(Rh@CeO
2
) catalysts was observed at 650
°C.
3
Since then, the conversion of ethanol
into hydrogen gas over ceria (CeO
2
) has
been widely investigated and makes a good
prototypical reaction to study the effects of
biotemplating and nanocrystallinity on
catalytic performance.
3-24
The overall oxi-
dative steam reforming reaction is
and is slightly exothermic with H
R
-50
kJ/mol, allowing for autothermal operation
when combined with a limited amount of
total combustion.
3
In this reaction, water is
consumed, so the molar ratio of H/C in the
product stream is not equal to the ratio
found in ethanol (3:1).
Combining rhodium with nickel on
CeO
2
(Rh-Ni@CeO
2
) enhances the ability of
the catalyst to oxidatively steam reform eth-
anol, especially at low temperatures.
6,10
The
presence of both nickel and rhodium allows
for the efficient decomposition of ethanol
to smaller molecules through C-C bond
cleavage, as well as the conversion of meth-
ane, CO, and H
2
O to H
2
and CO
2
. Nickel
alone tends to produce more acetaldehyde
than the mixed system, and rhodium alone
tends to produce large amounts of CO and
CH
4
compared to the mixed system. Nickel
is highly active in the steam reforming nec-
essary to convert methane and methanol
into hydrogen and carbon dioxide in the
presence of water and also to allow for the
water gas-shift reaction to convert residual
carbon monoxide and water into hydrogen
and carbon dioxide.
6,25
*Address correspondence to
belcher@mit.edu.
Received for review February 19, 2010
and accepted May 24, 2010.
Published online June 7, 2010.
10.1021/nn100346h
© 2010 American Chemical Society
C
2
H
5
OH + 2H
2
O + 1/2O
2
f 2CO
2
+ 5H
2
(1)
ABSTRACT For decades, ethanol has been in use as a fuel for the storage of solar energy in an energy-dense,
liquid form. Over the past decade, the ability to reform ethanol into hydrogen gas suitable for a fuel cell has drawn
interest as a way to increase the efficiency of both vehicles and stand-alone power generators. Here we report
the use of extremely small nanocrystalline materials to enhance the performance of 1% Rh/10% Ni@CeO
2
catalysts
in the oxidative steam reforming of ethanol with a ratio of 1.7:1:10:11 (air/EtOH/water/argon) into hydrogen
gas, achieving 100% conversion of ethanol at only 300 °C with 60% H
2
in the product stream and less than 0.5%
CO. Additionally, nanocrystalline 10% Ni@CeO
2
was shown to achieve 100% conversion of ethanol at 400 °C with
73% H
2
, 2% CO, and 2% CH
4
in the product stream. Finally, we demonstrate the use of biological templating on M13
to improve the resistance of this catalyst to deactivation over 52 h tests at high flow rates (120 000 h
1
GHSV) at
450 °C. This study suggests that the use of highly nanocrystalline, biotemplated catalysts to improve activity and
stability is a promising route to significant gains over traditional catalyst manufacture methods.
KEYWORDS: ceria · catalyst · ethanol · fuel cell · hydrogen
ARTICLE
www.acsnano.org VOL. 4 ▪ NO. 6 ▪ 3227–3235 ▪ 2010 3227