## Durable ruthenium and graphene fuel cell catalyst matches performance of platinum alloys

##### 30 June 2017

Scientists at Rice University and their colleagues in China have fabricated a durable catalyst for high-performance fuel cells by attaching single ruthenium atoms to nitrogen-doped graphene. Catalysts that drive the oxygen reduction reaction in fuel cells are usually made of platinum. Platinum is expensive, however, and scientists have searched for decades for a suitable replacement.

The ruthenium-graphene combination may fit the bill, said chemist James Tour, whose lab developed the material with his colleagues at Rice and in China. The Ru/nitrogen- doped GO catalyst exhibits excellent four-electron ORR activity, offering onset and half-wave potentials of 0.89 and 0.75 V, respectively, vs a reversible hydrogen electrode (RHE) in 0.1 M HClO4, together with better durability and tolerance toward methanol and carbon monoxide poisoning than seen in commercial Pt/C catalysts. A paper on the work appears in the journal ACS Nano.

Fuel cells, which directly convert the chemical energy from fuel into electricity, have been recognized as electrocatalysts for PEMFCs. Several approaches have been implemented to reduce the usage of Pt, such as dispersing the promising candidates for efficient and clean energy conversion. A problem is that the sluggish four-electron oxygen reduction reaction (ORR) at the cathode in fuel cell systems remains a major technical challenge and severely limits its widespread commercialization. Currently, expensive and chemically sensitive Pt-based alloys are the most effective ORR electrocatalyst in proton exchange membrane fuel cells (PEMFCs), which are commonly a reliable system for practical application. But due to the harsh acidic environment and high oxidation potential required for PEMFC cathode operation, few materials are stable enough to be considered as ORR electrocatalysts for PEMFCs.

… much effort has been devoted to replacing the Pt-based electrocatalysts for ORR, and especially for use in acid media which is a required condition of PEMFCs. As the limit in downsizing metal morphology, the concept of single-atom catalysts (SACs) has emerged since it maximizes the exposed atom efficiency. However, the preparation of SACs remains challenging because the high free energy of individual metal atoms leads to metal aggregation, affording nanoclusters or nanoparticles, particularly under harsh acidic reaction conditions.

… Here, we report the synthesis of atomically dispersed Ru species embedded on a N-doped graphene matrix (Ru-N/G) via a facile technique using GO containing trace amounts of Ru salts as the precursor. … This Ru and N-doped graphene-based catalyst exhibits high performance and stability toward ORR in an acidic media with extraordinarily low overpotential. Computational studies suggest that a Ru-oxo species with nitrogen coordination contributes favorably to the origin of oxygen reduction activity.

—Zhang et al.

Ruthenium is often a highly active catalyst when fixed between arrays of four nitrogen atoms, yet it is one-tenth the cost of traditional platinum. And since we are using single atomic sites rather than small particles, there are no buried atoms that cannot react. All the atoms are available for reaction.

—James Tour

Spreading single ruthenium atoms across a sheet of graphene involved dispersing graphene oxide in a solution, loading in a small amount of ruthenium and then freeze-drying the new solution and turning it into a foam.

Baking that at 750 ˚C Celsius (1,382 ˚F) in the presence of nitrogen and hydrogen gas reduced the graphene and locked nitrogen atoms to the surface, providing sites where ruthenium atoms could bind.

 Schematic illustration of the synthetic process for the Ru-N/G catalyst annealed at 750 °C with NH3 (Ru-N/G-750). (I) GO is dispersed in deionized water. (II) Ru(NH3)6Cl3 is added into a GO solution followed by lyophilization; the dashed lines indicate the interaction between the Ru cation and GO. (III) Formation of the Ru-N/G-750 after annealing at 750 °C with NH3. The conversion of O2 to H2O is depicted. Credit: ACS, Zhang et al. Click to enlarge.

Materials made at higher and lower temperatures weren’t as good, and those made at the proper temperature but without either ruthenium or nitrogen proved the quality of the reaction depended on the presence of both.

The material showed excellent tolerance against methanol crossover and carbon monoxide poisoning in an acidic medium, both of which degrade the efficiency of fuel cells; such degradation is a persistent problem with traditional platinum fuel cells.

Lead authors of the paper are graduate students Chenhao Zhang of Rice and the Chinese Academy of Sciences, Shanghai; Junwei Sha of Rice, the Chinese Academy of Sciences and Tianjin University, China; and Juncai Dong and Dongliang Chen of the Chinese Academy of Sciences.

Co-authors are alumni Huilong Fei, Mingjie Liu and Qifeng Zhong, postdoctoral researchers Sadegh Yazdi and Xiaolong Zou and graduate student Jibo Zhang; Emilie Ringe, an assistant professor of materials science and nanoengineering, and Boris Yakobson, the Karl F. Hasselmann Professor of Materials Science and NanoEngineering and a professor of chemistry, all of Rice; Naiqin Zhao of Tianjin University and the Collaborative Innovation Center of Chemical Science and Engineering, Tianjin, China; and Haisheng Yu and Zheng Jiang of the Chinese Academy of Sciences.

Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of computer science and of materials science and nanoengineering at Rice.

The research was supported by the Air Force Office of Scientific Research and its Multidisciplinary University Research Initiative, the China Scholarship Council, the American Chemical Society Petroleum Research Fund, the Department of Energy, the Robert Welch Foundation, the National Natural Science Foundation of China and the Jianlin Xie Foundation of the Institute of High Energy Physics, Chinese Academy of Science.

Resources

• Chenhao Zhang, Junwei Sha, Huilong Fei, Mingjie Liu, Sadegh Yazdi, Jibo Zhang, Qifeng Zhong, Xiaolong Zou, Naiqin Zhao, Haisheng Yu, Zheng Jiang, Emilie Ringe, Boris I. Yakobson, Juncai Dong, Dongliang Chen, and James M. Tour (2017) “Single-Atomic Ruthenium Catalytic Sites on Nitrogen-Doped Graphene for Oxygen Reduction Reaction in Acidic Medium” ACS Nano doi: 10.1021/acsnano.7b02148

Eventually, in the near future, machine made mass produced FCs, without expensive platinum alloy, should cost less and compete with low cost ICEs.

H2 from more efficient electrolyzers and excess-surplus REs will also cost less and compete with fossil fuels.

Both will be around before 2025?

The price of ruthenium has recently gone up by almost 100% to $65/Oz and could go up 2X to 5+X due to very low production and relative rarity. Usage per FC would have to be reduced? High temperature PEM fuel cells use phosphoric acid on the cathode, so no platinum required there. SOFCs use NO platinum at all. Once they get the platinum required for a car down to that used in catalytic converters they will have reached parity. According to Charlie Freese, GM's head of global fuel cell engineering, the GM/Honda alliance had the amount of platinum down to 10 grams or about$350 worth per FC vehicle. There seems to be a 25 to 30 thousand dollar premium on FC vehicles today. Removing 100% of that $350 from cost of goods sold isn't going to be enough to reach parity with ICE which has also reduced their platinum usage from 3-7 grams to 2-4 per vehicle. Platinum has consistently been in the$30-\$40 per gram for a few years now.

FCs, equivalent to 4-cyl and 6-cyl will, with full automation and lower raw materials, be produced at equivalent or lower cost to ICEs by 2025 or so.

By then, extended range PHEVs, with small FCs for extended range and pure FCEVs with low power small battery, will become cheaper than equivalent extended range BEVs and competitive with ICEVs.

Replacing the ICE with a small FC on extended range hybrids will be a strong possibility at no extra cost.

>FCs, equivalent to 4-cyl and 6-cyl will, with full automation and lower raw materials, be produced at equivalent or lower cost to ICEs by 2025 or so.

By 2025 long range BEVs are expected to be cheaper than ICEVs. Hopefully long before they will figure out that midrange BEVs with fast charging and a decent charging infrastructure are more cost effective.

I honestly think there will be battery advances way before these fuel cells can hit the market and make a sufficient impact.

The year 2025 is light-years behind improved batteries IMO.

Then again, I may be wrong.

Everybody say that future fuelcell and future batteries will be better and cheaper. Conclusion don't buy any actual bev or fuelcell car because it ain't ready and don't buy an ice car because it pollute like mad. The only solution is to buy a used cheap ice car for the moment and drive it slow.

Also in the near future nissan will release a cheap gas serial hybrid doing easily over 120 mpg with a small ice generator with exhaust pressure and heat re-circulation

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