Bathed in simulated sunlight, this photoelectrolysis cell in the lab of Song Jin splits water into hydrogen and oxygen using a catalyst made of the abundant elements cobalt, phosphorus and sulfur. Image: David Tenenbaum/University of Wisconsin-Madison.A major roadblock to the widespread use of hydrogen as a fuel is the need for platinum or other expensive noble metals to catalyze the splitting of water into hydrogen and oxygen. "In the hydrogen evolution reaction, the whole game is coming up with inexpensive alternatives to platinum and the other noble metals," says Song Jin, a professor of chemistry at the University of Wisconsin-Madison.
In Nature Materials, Jin's research team now reports their development of a novel hydrogen-generating catalyst containing phosphorus and sulfur – both common elements – and cobalt, a metal that is 1000 times cheaper than platinum. According to Jin, this new catalyst is almost as efficient as platinum and likely shows the highest catalytic performance among the non-noble metal catalysts reported so far.
The advance emerges from a long line of research in Jin's lab focused on the use of iron pyrite (fool's gold) and other inexpensive, abundant materials for energy transformation. Jin and his students Miguel Cabán-Acevedo and Michael Stone came up with the new high-performing catalyst by replacing iron with cobalt to make cobalt pyrite, and then added phosphorus.
As well as being inexpensive, this new catalyst can also be powered purely by sunlight. Although electricity is the usual energy source for splitting water into hydrogen and oxygen, "there is a lot of interest in using sunlight to split water directly," 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," he explains. "Because this new catalyst is so much better and so close to the performance of platinum, we immediately asked WARF (the Wisconsin Alumni Research Foundation) to file a provisional patent, which they did in just two weeks."
Nevertheless, many questions remain about a catalyst that has only been tested in the lab. "One needs to consider the cost of the catalyst compared to the whole system,” says Jin. “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."
For replacing platinum with catalysts made from cheaper, more abundant materials is not just a question of cost, but also of practicality. "If you want to make a dent in the global warming problem, you have to think big,” reports Jin. “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."
This story is adapted from material from the University of Wisconsin-Madison, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.