Another Photoelectrolysis Method With Iron Oxide

Technion-Israel Institute of Technology researchers have found another design to split water molecules into hydrogen and oxygen using iron oxide.

The news follows by a day yesterday’s release by Kevin Sivula and his colleagues at Ecole Polytechnique Fédérale de Lausanne (EPFL).  Who is first may be a notable question in the coming months and years.  But for now – there are differences.

Lead researcher Associate Prof. Avner Rothschild, of the Department of Materials Science and Engineering at Technion-Israel Institute (TII) said, “We have found a way to trap light in ultrathin films of iron oxide that are 5,000 times thinner than typical office paper.  This is the enabling key to achieving high efficiency and low cost. ”

The TII work, very simply explained suggests they are working with a one step process film using iron oxide while the EPFL work is using another layer with titanium dioxide.  The TII press release and paper abstract published this week in Nature Materials isn’t clear on the full process to the extent that EPFL has provided.

A quick refresh – iron oxide is a common semiconductor material, inexpensive to produce, stable in water, and – unlike other semiconductors such as silicon – can oxidize water without itself being oxidated, corroded, or decomposed.  But it isn’t a good electrical conductor.  The TII press release points out getting from light to a photogenerated charge carrier before the charges die out by recombination is a problem

Prof. Rothschild explains his teams route, “Our light-trapping scheme overcomes this tradeoff, enabling efficient absorption in ultrathin films wherein the photogenerated charge carriers are collected efficiently. The light is trapped in quarter-wave or even deeper sub-wavelength films on mirror-like back reflector substrates. Interference between forward- and backward-propagating waves enhances the light absorption close to the surface, and the photogenerated charge carriers are collected before they die off.”

Now this team also has a breakthrough.  It could make possible the design of inexpensive solar cells that combine ultrathin iron oxide photoelectrodes with conventional photovoltaic cells based on silicon or other materials to produce electricity and hydrogen.  According to Prof. Rothschild, these cells could store solar energy for on demand use, 24 hours per day.

These technologies are strong contrasts to conventional photovoltaic cells, which provide power only when the sun is shining and not at night or when it is cloudy.  They make fuel when they sun activates them and can bleed the fuel off for use as needed.  While not electricity, the storage problem of batteries and an inverter is skipped.  Straight to fuel is a worthwhile economic choice.

The TII take is interesting in another way.  Rothschild suggests the panels could be dual function generating hydrogen fuel as well as electrical power.  Whether or not that economic choice has legs begs a lot more information.

The curious thing is the almost simultaneous announcements of two somewhat different methods.  The facts speak to observers that the research has breadth already and good prospects.  The attractiveness of making one’s own fuel on the roof is a very interesting idea.

The TII news is very thin.  How much depth they could provide isn’t known and that’s where the EPFL information gets a lead.  Which technology is the leader can only be learned over time.

One hopes that both have strong enough and compelling enough production, efficiency and investment expense to get a good marketplace start.  Both are still years out – but the race is likely on, and that is a very very good thing for almost everyone.

The starting gun has just went off . . .  its will be a grand competition.

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