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SLAC, U Toronto team develops new highly efficient ternary OER catalyst for water-splitting using earth-abundant metals; >3x TOF prior record-holder

Scientists from the Department of Energy’s SLAC National Accelerator Laboratory and the University of Toronto have developed a new type of ternary catalyst for the oxygen evolution reaction (OER) in water-splitting that exhibits a turnover frequency (TOF) that’s more than three-times above the TOF and mass activities of optimized control catalysts and the state-of-art NiFeOOH catalyst.

The research, published in the journal Science, outlines a potential way to make a future generation of water-splitting catalysts from three abundant metals—iron (Fe), cobalt (Co) and tungsten (W)—rather than the rare, costly metals on which many of today’s catalysts rely. The gelled FeCoW oxy-hydroxide material exhibits the lowest overpotential (191 mV) reported at 10 mA per square centimeter in alkaline electrolyte. Further, the ternary catalyst showed no evidence of degradation following more than 500 hours of operation.

The good things about this catalyst are that it’s easy to make, its production can be very easily scaled up without any super-advanced tools, it’s consistent, and it’s very robust.

—Aleksandra Vojvodic, a SLAC staff scientist with the SUNCAT Center for Interface Science and Catalysis who led the theoretical side of the work

In previous work, Vojvodic and her SUNCAT colleagues had used theory and computation to look at water-splitting oxide catalysts that contain one or two metals and predict ways to make them more active. For this study, Edward H. Sargent, a professor of electrical and computer engineering at the University of Toronto, asked them to look at the effect of adding tungsten to an iron-cobalt catalyst that worked, but not very efficiently.

The bottleneck in improving water-splitting technologies is the oxygen-evolving reaction (OER), where even the most efficient precious-metal catalysts require a substantial overpotential to reach the desired current densities ≥10 mA cm−2. Researchers have explored earth-abundant first-row (3d) transition metal oxides, including 3d metal oxy-hydroxides, oxide perovskites, cobalt phosphate composites, nickel borate composites, and molecular complexes. The OER performance of multimetal oxides based on Fe, Co, and Ni is particularly promising, and OER activity often outperforms that of the corresponding single-metal oxides.

We examined whether multimetal oxide OER catalysts could be improved by systematically modulating their 3d electronic structure.

—Zhang et al.

With the aid of powerful computers at SLAC and elsewhere and state-of-the-art computational tools, the SUNCAT team determined that adding tungsten should significantly increase the catalyst’s activity—especially if the three metals could be mixed so thoroughly that their atoms were uniformly distributed near the active site of the catalyst, where the reaction takes place, rather than separating into individual clusters as they normally tend to do.

Tungsten is quite a large atom compared to the other two, and when you add a little bit of it, it expands the atomic lattice, and this affects the reaction not only geometrically but also electronically. We were able to understand, on the atomic scale, why it works, and then that was verified experimentally.

—Aleksandra Vojvodic

Based on that information, Sargent’s team developed a novel way to distribute the three metals uniformly within the catalyst: They dissolved the metals and other ingredients in a solution and then slowly turned the solution into a gel at room temperature, tweaking the process so the metal atoms did not clump together. The gel was then dried into a white powder whose particles were riddled with tiny pores, increasing the surface area where chemicals can attach and react with each other.

F2.large
Schematic illustration of preparation process for the gelled structure and pictures of corresponding sol, gel and gelled film. Credit: AAAS, Zhang et al. Click to enlarge.

In tests, the catalyst was able to generate oxygen gas three times faster, per unit weight, than the previous record-holder, Sargent said, and it also proved to be stable through hundreds of reaction cycles.

It’s a big advance, although there’s still more room to improve. And we will need to make catalysts and electrolysis systems even more efficient, cost effective and high intensity in their operation in order to drive down the cost of producing renewable hydrogen fuels to an even more competitive level.

—Edward Sargent

Sargent said the researchers hope to use the same method to develop other three-metal catalysts for splitting water and also for splitting carbon dioxide, a greenhouse gas released by burning fossil fuels, to make renewable fuels and chemical feed stocks. He and five other members of the University of Toronto team have filed for a provisional patent on the technique for preparing the catalyst.

There are a lot of things we further need to understand. Are there other abundant metals we can test as mixtures in oxides? What are the optimal mixtures of the components? How stable is the catalyst, and how can we scale up its production? It needs to be tested at the device level, really.

—Aleksandra Vojvodic

Jeffrey C. Grossman, a professor of materials science and engineering at MIT who was not involved in the study, said:

he work impressively highlights the power of tightly coupled computational materials science with advanced experimental techniques, and sets a high bar for such a combined approach. It opens new avenues to speed progress in efficient materials for energy conversion and storage.

SLAC research associate Michal Bajdich and Stanford postdoctoral researcher Max García-Melchor also contributed to this work, along with researchers from the DOE’s Brookhaven National Laboratory; East China University of Science & Technology, Tianjin University and the Beijing Synchrotron Radiation Facility in China; and the Canadian Light Source. The research was funded by a number of sources, including the Ontario Research Fund – Research Excellence Program, Natural Sciences and Engineering Research Council of Canada and the CIFAR Bio-Inspired Solar Energy Program, as well as the DOE Office of Science, which funds SUNCAT, and the SLAC Laboratory Directed Research and Development program.

Resources

  • Bo Zhang, Xueli Zheng, Oleksandr Voznyy, Riccardo Comin, Michal Bajdich, Max García-Melchor, Lili Han, Jixian Xu, Min Liu, Lirong Zheng, F. Pelayo García De Arquer, Cao Thang Dinh, Fengjia Fan, Mingjian Yuan, Emre Yassitepe, Ning Chen, Tom Regier, Pengfei Liu, Yuhang Li, Phil De Luna, Alyf Janmohamed, Huolin L. Xin, Huagui Yang, Aleksandra Vojvodic, Edward H. Sargent (2016) “Homogeneously dispersed, multimetal oxygen-evolving catalysts” Science doi: 10.1126/science.aaf1525

Comments

gorr

Learn to do synthetic gasoline with low cost water splitting and co2 capture and put this gasoline for sale at a lower cost near where i live.

HarveyD

This could lead to much lower cost clean H2 using excess REs

Coupled with efficient fixed and mobile SS H2 storage tanks, tomorrow's FCEVs could rely on abondant supply of low cost clean H2.

May become a breakthrough for FCEVs and REs with storage.

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