Rice University scientists have developed a new single, robust catalyst that splits water into hydrogen and oxygen with Earth-abundant materials that approach the efficiency of more expensive platinum.

A film of high-surface-area nickel foam coated with graphene and a compound of iron, manganese and phosphorus serve as a water-splitting catalyst that can produce hydrogen and oxygen simultaneously. The material was created at Rice University and tested at the University of Houston.  Image Credit: Photo by Jeff Fitlow. Click image for the largest view.

The electrolytic film produced at Rice and tested at the University of Houston is a three-layer structure of nickel, graphene and a compound of iron, manganese and phosphorus. The foamy nickel gives the film a large surface, the conductive graphene protects the nickel from degrading and the metal phosphide carries out the reaction.

The team’s research paper about the new material is the subject of a paper in Nano Energy.

Rice chemist Kenton Whitmire and Houston electrical and computer engineer Jiming Bao and their labs developed the film to overcome barriers that usually make a catalyst good for producing either oxygen or hydrogen, but not both simultaneously.

Whitmire explained, “Regular metals sometimes oxidize during catalysis. Normally, a hydrogen evolution reaction is done in acid and an oxygen evolution reaction is done in base. We have one material that is stable whether it’s in an acidic or basic solution.”

The discovery builds upon the researchers’ creation of a simple oxygen-evolution catalyst revealed earlier this year. In that work, the team grew a catalyst directly on a semiconducting nanorod array that turned sunlight into energy for solar water splitting.

This electron microscope image shows nickel foam coated with graphene and then the catalytic surface of iron, manganese and phosphorus. Image Credit: Desmond Schipper. Click image for the largest view.

Electrocatalysis requires two catalysts, a cathode and an anode. When placed in water and charged, hydrogen will form at one electrode and oxygen at the other, and these gases are captured. But the process generally requires costly metals to operate as efficiently as the Rice team’s catalyst.

Whitmire said, “The standard for hydrogen evolution is platinum. We’re using Earth-abundant materials – iron, manganese and phosphorus – as opposed to noble metals that are much more expensive.”

The new catalyst also requires less energy, Whitmire explained. “If you want to make hydrogen and oxygen, you have to put in energy, and the more you put in, the less commercially viable it is. You want to do it at the minimum amount of energy possible. That’s a benefit of our material: The overpotential (the amount of energy required to trigger electrocatalysis) is small, and quite competitive with other materials. The lower you can get it, the closer you come to making it as efficient as possible for water splitting,” he said.

Graphene, the atom-thick form of carbon, is key to protecting the underlying nickel. One to three layers of graphene are formed on the nickel foam in a chemical vapor deposition (CVD) furnace, and the iron, manganese and phosphorus are added on top of that, also via CVD and from a single precursor.

Tests by Bao’s lab compared nickel foam and the phosphide both with and without graphene in the middle and found the conductive graphene lowered charge-transfer resistance for both hydrogen and oxygen reactions.

Co-lead author Desmond Schipper, a Rice graduate student explained, “Nickel is one of the best catalysts to make graphene. Essentially, we’re using the nickel to help improve the nickel.” He said the manganese adds a level of protection as well.

Whitmire said the material is scalable and should find use in industries that produce hydrogen and oxygen or by solar- and wind-powered facilities that can use electrocatalysis to store off-peak energy.

It may also be adapted to produce other advanced materials. “Our method could be widely applicable to a large number of metal phosphide materials for catalysts – not just for water splitting, but for a range of things,” he said.

“A critical factor is that we’re able to make phase-pure materials with different compositions. Currently, people have very little control over the phase they get on a surface, and in many cases they get a mixture. When that happens, they don’t know which phase is actually responsible for the catalysis. With our process, they can know.”

This is top of the line innovation in catalysts. Hydrogen production, while on most everyone’s list, is much harder to do at scale than most everyone realizes. If industry and small business can finally make economically free hydrogen fuel with this technology then the hydrogen economy could get started.


2 Comments so far

  1. Matt Musson on August 2, 2017 7:01 AM

    I believe these metal foams are going to unleash a whole slue of new and interesting products. But, right now people are still trying to figure out what to do with them.

  2. Sorting machine on August 6, 2017 8:59 PM

    Quite a great post for people. I like.

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