Transcript A Chemical Approach to Solar Energy

A New Catalyst for Splitting Water
into Molecular Oxygen
James M. Krier
UC-Berkeley
Unique challenges ahead
Energy = N (GDP/N)(E/GDP)
Per person
GDP
Energy
intensity
Even with optimistic
technological and
conservation forecasts,
the rapid economic
growth in developing
nations is predicted to
double global energy
needs by 2050
N. S. Lewis, D. G. Nocera, Proc. Natl. Acad. Sci. U.S.A. 103, 15729 (2006).
Power from the sun
2 H2(g) + O2(g) → 2 H2O(l)
∆H = -286 kJ/mol
bcs.whfreeman.com/lehninger
• Enough solar energy strikes
the globe in one hour (4.3 x
1020 J) to power all human
activity for one year (4.1 x
1020 J)
• Photosynthesis by plants is
an example of splitting water
for energy storage
N. S. Lewis, D. G. Nocera, Proc. Natl. Acad. Sci. U.S.A. 103, 15729 (2006).
The artificial plant
The oxygen reaction is tricky in both systems
N. S. Lewis, D. G. Nocera, Proc. Natl. Acad. Sci. U.S.A. 103, 15729 (2006).
Recent breakthrough
e-
e+
-
1.29 V
Conducting glass, such as indium tin oxide
0.5 mM Co(NO3)2
0.1 M KPi (potassium phosphate)
SEM image
Alternative:
Kanan, M. W. & Nocera, D. G. Science 321, 1072–1075 (2008).
Film is 2:1 as Co:Pi
Key features
• Self-repair mechanism, in situ formation
• Co2+, Co3+, Co4+ species likely responsible for balancing
different oxidation steps
• Co2+-HPO42- (aq)  Co3+-HPO42- (on electrode surface)
• Composed of earth-abundant materials
• Long lasting O2 production at low overpotential, neutral pH, room
temperature/pressure
• Drawbacks: large initial overpotential, not effective at high current
Kanan, M. W. & Nocera, D. G. Science 321, 1072–1075 (2008).
web.mit.edu/newsoffice/2008/oxygen-0731.html
Your new house?
Kanan, M. W. & Nocera, D. G. Science 321, 1072–1075 (2008).
Links to additional reading…
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nature.com/nmat/journal/v7/n10/full/nmat2284.html
rsc.org/ej/CS/2009/b802262n.pdf
sciencemag.org/cgi/reprint/321/5892/1072.pdf
www.web.mit.edu/newsoffice/2008/oxygen-0731.html
www.pnas.org/content/103/43/15729.abstract