Another Approach to Solar Storage

Plants have this whole solar thing down.

They use the sun’s rays to convert water into energy by breaking its chemical bonds, storing the excess as sugar for later use when sunlight may not be available. Sounds simple - water is relatively easy to split into its constituent elements oxygen and hydrogen via electrolysis - but until now cost-effectiveness and storage have remained hurdles for researchers hoping to emulate the photosynthetic process. If it could be produced cheaply enough, hydrogen could become a viable replacement for fossil fuels. Current electrolytic techniques use prohibitively expensive platinum as a catalyst, however, as do the fuel cells in which the hydrogen is stored and reconverted. Now two MIT researchers have developed a more affordable method.

Matthew Kanan and Daniel Nocera have found that, by substituting much cheaper cobalt and phosphates for platinum and running a mild electrical current through the solution via a glass electrode, they could extract oxygen from water in a similar manner. The excess protons left behind during oxygen formation migrate to a second electrode - still typically platinum - and assemble into hydrogen molecules as they pair with available electrons. This hydrogen could then be stored in fuel cells until it is needed. This means that photovoltaic panels could be used both to generate energy for immediate use and create excess energy for storage in the form of hydrogen. Nocera believes that, within ten years, cobalt-based reactions could be combined with pV arrays to power most homes and buildings.

Cheap, easy and efficient, this new process is being hailed as a “major discovery”. At the very least, it is a significant upgrade over the cumbersome and costly alternatives. According to James Barber, the Ernst Chain Professor of Biochemistry at Imperial College London, “The importance of their discovery cannot be overstated since it opens up the door for developing new technologies for energy production…”

And another development may make the process even more practical. While Kanan and Nocera’s discovery greatly diminishes the need for platinum as a catalyst, this expensive metal is still needed in the form of that second electrode to help form hydrogen after the water molecules have been broken apart and in fuel cell cathodes to reverse the process, reconstituting the stored hydrogen with oxygen to create usable energy and water (as a byproduct). Bjorn Winther-Jensen, a researcher at the ARC Centre for Excellence in Materials Science in Australia, and his team appear to have partly addressed this problem by developing new fuel cell cathodes made from a conducting polymer called poly(3,4-ethylenedioxythiphine) coated onto a Goretex membrane, which provides a surface area large enough to produce the oxygen needed for recombination at similar rates to platinum cathodes.

Compared to the $1700 to $2000 pricetag for an ounce of platinum, the polymer costs a miniscule $57 an ounce. The amount of platinum needed to run a conventional automobile fuel cell alone would cost $3500-$4000, as opposed to only several hundred dollars for new polymer-based fuel cells generating the equivalent amount of current. And the polymer substitute has other significant benefits, as well. Platinum cathodes become less effective if the platinum nanoparticles clump together or react with carbon monoxide. The new polymer cathodes suffer no such drawbacks.

There are still some details to be worked out. For instance, though these developments significantly reduce the amount of platinum needed, some is still necessary to create hydrogen during the electrolytic process. However, Nocera believes that it is simply a matter of time before another substitute is found. The same must go for the fuel cells themselves, if these breakthroughs are to work on a large scale. Winther-Jensen’s team is now working on developing a three-dimensional fuel cell to support thicker electrodes and increase the amount of surface area available for generating current.

Wherever these developments ultimately lead, they have raised hydrogen’s profile from a dark horse to a legitimate contender in the crowded field of renewables staking their claim as the next big thing, and they may have taken a step toward solving the problem of solar storage. Both Kanan and Nocera’s announcement and that of Winther-Jensen’s team were published in the August 1 issue of Science. Also, click here to read the transcript of an interview with Winther-Jensen.


Posted on Friday, January 11th, 2008 at 2:01 pm | Tagged in Energy, Energy Efficiency, Photovoltaics, Renewables, Sustainability, Technology | posted by Bill

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