Synthesis of Strained Metal Nanocrystal Architectures for Energy Conversion Electrocatalysis

Abstract

In order to understand the lattice strain effect and its relationship to size, shape, composition, and catalytic performance, novel well-defined nanocrystal archetypes were designed and synthesized by taking advantage of wet chemical, seed-mediated (mild) reduction routes developed by our lab. First, the current synthesis challenges are addressed in creating smaller monometallic shape-controlled metal nanocrystals, and novel cuboctopods via a hybrid nanoparticle stabilizer. A look at the relationship between lattice strain and morphology is then shown in a single-component system, where still new features have been observed for the first time by the traditional technique of powder x-ray diffraction. Synthesis methods for differently strained Pd surfaces are described and catalysis by these surfaces is discussed. Finally, studies of the synthesis, characterization, electrocatalytic activity, and restructuring of novel and more sophisticated strained architectures are presented: core-island-shell nanocrystals, phase-segregated nanoboxes, island nanoframeworks, and core-sandwich-shell nanoparticles. Lattice strain and composition effects were studied in carbon monoxide, small alcohol, and formic acid electrocatalytic oxidations as well as in oxygen reduction, the latter of which, governs the commercial viability of automotive fuel cells, a sustainable energy and zero-emission technology. Here it is demonstrated how a tunable thickness of Ni sandwich layers can be used to improve catalytic performance by increasing lattice strain on the Pt surface. The sandwich archetype offers a new platform for the investigation of lattice strain and could be a promising, industrially relevant, catalyst design concept, to help address the need for a more sustainable energy future. The results help paint a new picture of catalysis by metal nanocrystals; one which brings lattice strain to the forefront of the discussion, as an important parameter for further study and for use in developing higher-performing catalysts.