Researchers at Northwestern University have developed a new approach for creating new catalysts to aid in clean energy conversion and storage. The design method, reported in a paper in the Proceedings of the National Academy of Sciences, (PNAS) also has the potential to impact the discovery of new optical and data storage materials, catalysts that impact pharmaceutical synthesis and catalysts that allow for higher efficiency processing of petroleum products at much lower cost.

It is a major challenge in catalysis to uncover structure–performance relationships that drive the design and optimization of high-performance/low-cost catalysts. When one considers the number of potential elemental combinations for catalysts and then includes variables, such as particle size and elemental stoichiometry, the number of possibilities is daunting. There are also significant challenges facing the synthetic chemist, who is tasked with making and characterizing such complex architectures.

Indeed, a way of substantially narrowing the field is essential. In this work, we introduce an effective approach that combines computational prediction, experimental verification using a well-defined nanomodel, and finally production of high-performance catalysts in bulk as a powerful tool for discovering and designing catalysts for energy conversion and storage.

—Huang et al.

In this study, researchers looked at the challenges of improving affordability and catalyst efficiency in the conversion and storage of clean energy. Currently, platinum-based (Pt) catalysts are the most effective and commonly used to facilitate a hydrogen evolution reaction (HER), which is, in part, the basis for how fuel cells are used to generate energy. However, as platinum is rare and costly, scientists have been seeking more affordable and efficient alternatives.

We combined theory, a powerful new tool for synthesizing nanoparticles and more than one metallic element—in this case, an alloy consisting of platinum, copper and gold—to create a catalyst that is seven times more active than state-of-the-art commercial platinum.

—Professor Chad A. Mirkin, co-corresponding author

The researchers utilized scanning probe block copolymer lithography (SPBCL), along with density-functional theory (DFT) codes, to design and synthesize the HER catalyst. Invented in Mirkin’s lab at Northwestern, SPBCL enables scientists to control the growth and composition of individual nanoparticles patterned on a surface.

SPBCL confines metal precursors within individual polymer nanoreactors. Each nanoparticle grows by consuming the precursors within the polymer reactor, isolated from the growth of other nanoparticles, allowing the uniformity of nanoparticles in terms of size, phase structure, and composition to be precisely controlled.

The DFT codes outline the structural, magnetic and electronic properties of molecules, materials and defects.

Process for synthesizing nanoparticles by SPBCL and then studying their HER catalytic properties. (i) PPL is used to pattern PEO-b-P2VP nanoreactors, loaded with the appropriate metal salts, onto a glassy carbon substrate. Each nanoreactor has a near-identical volume and contains approximately the same number and type of atoms. (ii) The metal ion contents of the nanoreactors are thermally transformed into nanoparticles under a reducing environment. (iii) The patterned substrate is then used as a working electrode in a three-electrode cell to study HER catalysis. A, current reading; V, voltage. Huang et al. Click to enlarge.

… we have introduced SPBCL combined with DFT calculations as a powerful platform for catalyst discovery, design, optimization, and synthesis. The focus of this work has been on HER catalysts, and we have used these techniques to identify a structure (1:1:1 PtAuCu alloy particles) that exhibits a mass activity seven times greater than a commercial Pt/C catalyst (based on Pt content).

However, these techniques and observations, in principle, can be extended to many other reactions, providing a means of discovering promising new catalyst structures as well as a method for refining them to achieve optimum performance. With recent developments in PPL [polymer pen lithography] technology, pen arrays with as many as 11 million tips enable large-scale fabrication of nanoparticle arrays with programmable specifications such as size, shape, and composition, providing a route to the high-throughput screening and discovery of new catalysts.

—Huang et al.

This may include providing a clear path to new high-temperature superconductors; structures useful in data storage; materials for solar energy conversion nanostructures to move light around at the tiniest of scales; and new catalysts for converting low-value (affordable) chemicals into high-value products, such as pharmaceuticals and pharmaceutical precursors.

Identifying new materials is essential for driving technological development. The global catalysis market is expected to reach $34.3 billion in the next six years, according to a report by Grand View Research, Inc.

Resources

• Liliang Huang, Peng-Cheng Chen, Mohan Liu, Xianbiao Fu, Pavlo Gordiichuk, Yanan Yu, Chris Wolverton, Yijin Kang, Chad A. Mirkin (2018) “Catalyst design by scanning probe block copolymer lithography” PNAS doi: 10.1073/pnas.1800884115