Bathed in simulated sunlight, this photoelectrolysis cell in the lab of Song Jin, a professor of chemistry at the University of Wisconsin-Madison, splits water into hydrogen and oxygen using a catalyst made of the abundant elements cobalt, phosphorus and sulfur. Credit: David Tenenbaum/University of Wisconsin-Madison
Jin’s research team reports a hydrogen-making catalyst containing phosphorus and sulfur – both common elements – and cobalt, a metal that is 1,000 times cheaper than platinum. This is in answer to the major roadblock to “hydrogen economy”, ie the need for platinum or other expensive noble metals in the water-splitting devices. Noble metals are normally used as they resist oxidation and include many of the precious metals, such as platinum, palladium, iridium and gold.
Catalysts reduce the energy needed to start a chemical reaction. The new catalyst is almost as efficient as platinum and likely shows the highest catalytic performance among the non-noble metal catalysts reported so far. Jin and his students discovered the new high-performance catalyst by replacing iron to make cobalt pyrite, and then added phosphorus.
The new catalyst can also work with the energy from sunlight, Jin says. “We have demonstrated a proof-of-concept device for using this cobalt catalyst and solar energy to drive hydrogen generation, which also has the best reported efficiency for systems that rely only on inexpensive catalysts and materials to convert directly from sunlight to hydrogen.”
Many questions remain about a catalyst that has only been tested in the lab, Jin says. “One needs to consider the cost of the catalyst compared to the whole system. There’s always a tradeoff: If you want to build the best electrolyzer, you still want to use platinum. If you are able to sacrifice a bit of performance and are more concerned about the cost and scalability, you may use this new cobalt catalyst.”
Jin says. “If you want to make a dent in the global warming problem, you have to think big. Whether we imagine making hydrogen from electricity, or directly from sunlight, we need square miles of devices to evolve that much hydrogen. And there might not be enough platinum to do that.” http://news.wisc.edu/24010
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