Design of bimetallic catalysts and electrocatalysts through the control of reactive environments

Bimetallic nanocatalysts often exhibit enhanced performances, which are directly related to the specific atomic arrangements of the two metal elements on and near surface. It is thus important to control not only the overall but also, perhaps more critically, near surface compositions and structures. While many approaches have been developed for making bimetallic nanostructures with predetermined overall compositions, the control of surface structures with a high degree of accuracy is still a challenge. With the recent development of in situ tools such as environmental transmission electron microscopy (ETEM), dynamic structures under variable temperatures and reactive atmospheres can be studied quantitatively, laying the foundation for improved precision design of specific surface structures for catalysis. Herewith, we provide an overview of factors governing the dynamic processes of bimetallic restructuring. We first discuss the surface energetics of shaped bimetallic nanoparticles under gaseous environments, followed by examining the transformation of alloy nanoparticles into intermetallics and the key aspects in the preparation of intermetallic surfaces. Diffusion-controlled restructuring process is then presented, including the major recent developments in controlling the surface composition and formation of hollow structure from the Kirkendall process. Finally, we present selected bimetallic nanocatalysts to highlight their niche applications for electrochemical and heterogeneous reactions, especially those structurally sensitive ones, such as intermetallics, core-shell nanoparticles, and nanoframes. In situ ETEM, in this regard, can often be used to facilitate the understanding of dynamic structures under reactive conditions, thus a brief introduction is presented, focusing on the utilization of this technique in studying the bimetallic catalysts. (C) 2020 Elsevier Ltd. All rights reserved.