Fabrication of Faceted Metal Nanocrystal Electrodes By Solid-State Dewetting

Abstract

Electrochemical reactions are electrode-structure sensitive and hence microstructural properties of the (electro)-catalysts such as size, shape, exposed facets, and grain boundaries, among others, strongly affect the activity, selectivity, and stability.1, 2 Conventional methods based mainly on wet-chemistry have been widely adopted to synthesize nanocrystal (NC) electrocatalysts, and proved suitable to control their features. However, these methods require several synthesis steps, which increase the production time and complexity, and resulting particles often feature a complex composition (due to impurities such as ligands or templating agents) and suffer from durability issues, due e.g. to particle detachment from the substrates.We explore solid-state dewetting (SSD) as an alternative way to produce metal nanocrystal electrocatalysts while overcoming various challenges intrinsic of conventional approaches.3, 4 Dewetting is the heat induced agglomeration of thin metal films into particles. Taking Pt as a case study, we have investigated the effect of various SSD parameters such as metal film thickness, substrate crystallographic features, and dewetting conditions (time/temperature/atmosphere) on the physicochemical properties of the resulting dewetted metal NCs. Under optimized conditions, dewetting forms monodispersed faceted Pt nanocrystals of tunable size. Low- or high-index facets can be designed (as shown in the figure below) by tuning the substrate orientation and dewetting conditions (e.g., T, dewetting gas). In general, dewetted Pt NCs show higher (ESCA-normalized) activity towards hydrogen evolution reaction (HER) compared to Pt thin films, and their mass activity is comparable to the state-of-the-art Pt/C. The talk will delve into correlations between microstructure (grain size, shape and facets etc.) and the electrochemical performance of dewetted NCs.From a general point of view, dewetted NCs show intriguing electrochemical and mechanical properties, and hence dewetting appears to be a promising approach for preparing active and robust nanostructured (electro)-catalysts for various applications. In ongoing work, we investigate dewetting to deposit catalysts on gas diffusion layer (GDL) electrodes and test their performance in PEM lab-scale electrolyzers. Figure 1