PNNL

The Science                                

Grain boundaries (GBs) are a class of defects where two crystals meet and synergistically work as active sites for chemical conversions. However, they can be hard to grow in a controlled manner. Researchers developed a straightforward and scalable electricity-based way to synthesize assembles of noble metal nanoparticles (NPs). The NP assemblies are connected by GBs, the amount of which can be tuned by changing the voltage used during synthesis. Platinum (Pt) assemblies demonstrated extremely high activity for turning hydrogen into hydroxide in air via hydrogen oxidation. These assemblies enabled lowering the temperature of catalytic hydrogen sensing to room temperature for the first time.

The Impact

Numerous studies have found that GBs are highly active catalysts for a range of chemical reactions. The newly developed synthetic approach allows researchers to easily control the density of GBs in the networked material without changing the size of the nanoparticles. Compared to typical Pt-containing catalysts, the catalytic activity of these newly developed materials is significantly enhanced. These materials are so active for hydrogen, they can be used to detect hydrogen leaks at hydrogen fueling stations, pipelines, and fuel cell vehicles. The high activity of Pt assemblies for hydrogen oxidation may indicate similarly high activity of these assemblies for other reactions. This can help reduce the amount of critical materials, such as Pt, needed for catalysis and sensing.

Summary

Researchers developed a simple and scalable synthesis of Pt NP assemblies. The NPs are connected via GBs to form a larger network. In the electrolysis-driven reaction, oriented attachment and random collisions of NPs suspended in water lead to the formation of twin boundaries along (111) interfaces and highly mismatched GBs. Varying the electrolysis voltage allows researchers to control over the GB density without altering the size of the NP crystallites size or the GB type. The GB-rich Pt NP assemblies showed ultrahigh activity toward catalytic hydrogen oxidation in air compared to Pt NPs without the network structures. This high activity enabled room temperature catalytic hydrogen sensing for the first time. Simulations revealed that the unique geometry of the twin boundaries facilitates oxygen dissociation, drastically enhancing the hydrogen oxidation rate via the dissociative pathway. This new large-scale synthesis of the (111) twin GB-rich structures can help facilitate the development of a broad range of high-performance GB-rich catalysts. This synthesis can be extended to other metals, including palladium, gold, silver, and rhodium, with a goal of reducing the amount of critical materials needed for catalysis and sensing applications.

PNNL Contact

Dongsheng Li, Pacific Northwest National Laboratory, dongsheng.li2@pnnl.gov

Funding

This research was supported by the Department of Energy (DOE), Office of Science, Basic Energy Sciences program. The researchers also acknowledge support from the National Science Foundation. L.Z. and S.L. acknowledge support from the National Natural Science Foundation of China and start-up funds from Tsinghua University. This research used resources of the Advanced Photon Source; a DOE Office of Science user facility operated for the DOE by Argonne National Laboratory. The transmission electron microscopy work was supported by the DOE Early Career Research program and was conducted in EMSL, the Environmental Molecular Sciences Laboratory, a DOE user facility at Pacific Northwest National Laboratory. The authors also thank Hua Zhou and Xiaobing Zuo at Argonne National Laboratory for performing the small-angle X-ray scattering measurements.