Although it is simple in theory, splitting water into hydrogen and oxygen is a complex process, requiring two separate reactions — a hydrogen evolution reaction and an oxygen evolution reaction, each requiring a separate electrode.
Discovery could remove hurdle to producing hydrogen from water. University of Houston physicists have discovered a catalyst that can split water into hydrogen and oxygen, composed of easily available, low-cost materials and operating far more efficiently than previous catalysts. That would solve one of the primary hurdles remaining in using water to produce hydrogen. The catalyst, composed of ferrous metaphosphate grown on a conductive nickel foam platform, is far more efficient than previous catalysts, as well as less expensive to produce.
“Cost-wise, it is much lower and performance-wise, much better,” said Zhifeng Ren, M.D. Anderson professor of physics. The catalyst also is durable, operating more than 20 hours and 10,000 cycles in testing. “Some catalysts are outstanding but are only stable for one or two hours,” Ren said. “That’s no use.” Although it is simple in theory, splitting water into hydrogen and oxygen is a complex process, requiring two separate reactions – a H2 evolution reaction and an O2 evolution reaction, each requiring a separate electrode. While hydrogen is the more valuable component, it can’t be produced without also producing oxygen. And while efficient hydrogen catalysts are available, the lack of an inexpensive and efficient oxygen catalyst has created a bottleneck in the field.
Unlike solar power, wind power and other “clean” energy, hydrogen can be easily stored. Currently, most hydrogen is produced through steam methane reforming and coal gasification; those methods raise the fuel’s carbon footprint despite the fact that it burns cleanly. Chen said oxygen evolution reactions often depend upon an electrocatalyst using a “noble metal” – iridium, platinum or ruthenium. But those are expensive and not readily available.
“In this work, we discovered a highly active and stable electrocatalyst based on earth-abundant elements, which even outperforms the noble metal based ones,” she said. “Our discovery may lead to a more economic approach for hydrogen production from water electrolysis.” Water splitting can be triggered either through electric current or through photocatalysis, using the power of the sun. Direct solar-powered water splitting is too inefficient, as water can absorb just a small portion of the light spectrum. Ideally, Ren said, solar power would be used to generate the electric power used to split water. http://www.uh.edu/news-events/stories/2017/April/05152017Ren-Water-Catalyst.php
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