A New Catalyst for Splitting Water into Molecular Oxygen

James M. KrierUC-Berkeley

Unique challenges ahead

Energy = N (GDP/N)(E/GDP)

Even with optimistic technological and conservation forecasts, the rapid economic growth in developing nations is predicted to double global energy needs by 2050

Energy intensity

N. S. Lewis, D. G. Nocera, Proc. Natl. Acad. Sci. U.S.A. 103, 15729 (2006).

Per person GDP

Power from the sun

• 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

bcs.whfreeman.com/lehninger

2 H2(g) + O2(g) → 2 H2O(l)

∆H = -286 kJ/mol

N. S. Lewis, D. G. Nocera, Proc. Natl. Acad. Sci. U.S.A. 103, 15729 (2006).

The artificial plant

N. S. Lewis, D. G. Nocera, Proc. Natl. Acad. Sci. U.S.A. 103, 15729 (2006).

The oxygen reaction is tricky in both systems

Recent breakthrough

1.29 V

SEM image

Film is 2:1 as Co:Pi

Conducting glass, such as indium tin oxide

0.5 mM Co(NO3)2

0.1 M KPi (potassium phosphate)

e-e-

Kanan, M. W. & Nocera, D. G. Science 321, 1072–1075 (2008).

-+

Alternative:

Key features

• Self-repair mechanism, in situ formation• Co2+, Co3+, Co4+ species likely responsible for

balancing different oxidation steps

• Co2+-HPO42- (aq) Co3+-HPO4

2- (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 currentKanan, M. W. & Nocera, D. G. Science 321, 1072–1075 (2008).

Your new house?

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Kanan, M. W. & Nocera, D. G. Science 321, 1072–1075 (2008).

Links to additional reading… 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