Surface matters: using earth-abundant materials to split water for energy storage

Figure courtesy of Reference 1

Figure courtesy of Reference 1

The hydrogen fuel cell – the name elicits the fantasy of a future world where clean, quiet cars roam our tangle of highways without a carbon-dioxide care in the world. But this truly is nothing but a fantasy at this point, as fuel cell technology is still in early development phases for mass commercialization.

One of the largest obstacles to achieving a transportation economy powered by fuel cells is finding a cheap method of creating and storing hydrogen, the primary input for operation (and the basis for the so-called hydrogen economy). Solar-based water splitting has been the best, fossil-fuel-free bet to generate the necessary hydrogen, but finding an efficient way to do this with earth-abundant materials has been difficult. Now, new research1 in Nature Communications sheds some important light on the mechanisms limiting efficiency and has identified a way to improve performance using common elements.

Splitting water for hydrogen

If society ever wants to kick its petroleum habit, it will have to find a new way to store energy. Oil has been the easy source for decades, stored in an energy-dense, liquid form that is easy to transport in automobiles. Petroleum was also easy to find initially, but the world is running out of accessible fields.2 Even if this fossil fuel were still plentiful, transportation emissions now account for 28% of US greenhouse gas emissions,3 trailing only the electricity sector as the major culprit in global warming.

Hydrogen has always been a hopeful storage alternative since its compressed form stores three times as much energy per unit mass compared to oil. The problem lies in finding the element in its molecular form and storing it in a safe, reliable manner. Hydrogen molecules (H2) make up only 0.00055% of the atmosphere! Such scarcity results from hydrogen’s highly reactive nature such that most lone H atoms have already reacted with other elements to form water, methane, etc. Not the best start for thinking about a hydrogen economy! But a solution exists: separating hydrogen from these other molecules, such as water, and storing the resulting H2 molecules to use for power generation.

Water is relatively abundant on the planet relative to other materials used in the energy industry, which makes it a very promising source from which to generate hydrogen. The molecule is quite happy as it is, though, which means additional energy is required to break the bonds between hydrogen and oxygen to procure the hydrogen we need. Scientists have succeeded in constructing a simple device to provide this bond-breaking energy, but all the important work to be done involves finding the right materials to make the device cheap and efficient.

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Learn more about how scientists are improving water-splitting devices at the Eyes on Environment blog on Nature’s Scitable Network!

References

1)

Jang, J., Du, C., Ye, Y., Lin, Y., Yao, X., Thorne, J., Liu, E., McMahon, G., Zhu, J., Javey, A., Guo, J., & Wang, D. (2015). Enabling unassisted solar water splitting by iron oxide and silicon Nature Communications, 6 DOI: 10.1038/ncomms8447

2) Neuhauser, A. “Oil discoveries headed for new low.” US News and World Report, Accessed June 27, 2015.

3) EPA. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2012. Accessed June 27, 2015.

 

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