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New robust triple-layer bifunctional catalyst for water splitting with earth-abundant materials

A new robust and highly active bifunctional catalyst developed by Rice University and the University of Houston splits water into hydrogen and oxygen without the need for expensive metals such as platinum. The work, the team suggests, provides a facile strategy for fabricating highly efficient electrocatalysts from earth-abundant materials for overall water splitting.

The electrolytic film produced at Rice and tested at Houston is a three-layer structure of nickel, graphene and a ternary metal phosphide (FeMnP, 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. A paper on the work is published in the journal Nano Energy.

FeMnP exhibits high electrocatalytic activity toward both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Utilizing FeMnP/GNF as both the anode and the cathode for overall water splitting, the team achieved a current density of 10 mA cm−2 at a cell voltage of as low as 1.55 V with excellent stability. Complementary density functional theory (DFT) calculations suggested that facets exposing both Fe and Mn sites are necessary to achieve high HER activity.

IMG_0467
A catalyst developed by Rice University and the University of Houston splits water into hydrogen and oxygen without the need for expensive metals like platinum. This electron microscope image shows nickel foam coated with graphene and then the catalytic surface of iron, manganese and phosphorus. (Credit: Desmond Schipper/Rice University). Click to enlarge.

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 (OER) or hydrogen (HER), but not both simultaneously.

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.

—Kenton Whitmire

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.

The new catalyst also requires less energy, Whitmire said.

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.

—Kenton Whitmire

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.

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.

Zhenhuan Zhao of the University of Houston and the University of Electronic Science and Technology of China, Chengdu, is co-lead author of the paper. Co-authors are Andrew Leitner, Jing-Han Chen and Zhiming Wang of Rice and Hari Thirumalai, Lixin Xie, Fan Qin, Kamrul Alam, Lars Grabow, Shuo Chen, Dezhi Wang and Zhifeng Ren of the University of Houston. Whitmire is a professor of chemistry and associate dean of the Wiess School of Natural Sciences at Rice. Bao is an associate professor of electrical and computer engineering at the University of Houston and an adjunct professor at the University of Electronic Science and Technology of China.

Supporting the research were Rice University, the National Science Foundation (NSF) and the Robert A. Welch Foundation. Computing resources were provided by the University of Houston uHPC cluster, the NSF-supported Extreme Science and Engineering Discovery Environment and the Department of Energy Office of Science National Energy Research Scientific Computing Center.

Resources

  • Zhenhuan Zhao, Desmond E. Schipper, Andrew P. Leitner, Hari Thirumalai, Jing-Han Chen, Lixin Xie, Fan Qin, Md Kamrul Alam, Lars C. Grabow, Shuo Chen, Dezhi Wang, Zhifeng Ren, Zhiming Wang, Kenton H. Whitmire, Jiming Bao (2017) “Bifunctional metal phosphide FeMnP films from single source metal organic chemical vapor deposition for efficient overall water splitting,” Nano Energy, Volume 39, Pages 444-453, doi: 10.1016/j.nanoen.2017.07.027

Comments

Davemart

Some figures would have been nice.

HarveyD

Could this become one of many near future ways to split water to make much lower cost H2 with excess REs and/or solar energy?

If so, would the surplus oxygen created become an environmental problem?

With lower cost, higher efficiency mass produced FCs, their operation could become competitive with batteries and ICEs?

gorr

What these chaps are waiting for before beginning to make synthetic gasoline in the desert where there is free sun everyday. It will also be carbon neutral. These folks are horrendous and are there only to cash money for the green energy cartel and won't compete in a free market for any reasons whatsoever.

Alain

@Harvey,
The amount of O2 produced is minimal and the O2 is consumed to H2O again when the H2 is used.
When burning fossil fuel, O2 is taken out of the air and turned into CO2 and H2O. Nevertheless the O2 in the atmosphere has hardly decreased (even after a century pf burning fossils).

DaveD

This is incredible! Once they can produce H2 for the non existant HFCV fleet, I hear that next they'll come up with a way to add 10% to horse feed so we can feed all the horses we'll NEVER use in our fleet!!!

LOL

HarveyD

FC trains, buses, ships, trucks, light vehicles, tractors, etc will use most of the clean H2 that such procedure can produce.

Surplus H2 could be used to produce essential synthetic products?

SJC

Lots of solar/wind electricity to make h2/o2 with sequestered CO2 can make whatever liquid hydrocarbon fuel you want.

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