“Dewetted” Metal Nanoparticles As a Platform to Study Electrocatalytic Reactions

Abstract

Metal nanoparticles (NPs) are key for catalytic applications such as electrocatalysis. Besides morphology and composition, also structural features largely affect their performance [1]. Recent work uncovered correlations between exposed facets [2,3] and grain boundaries’ density [4,5] with nanoparticles’ activity, selectivity, and stability.The present contribution addresses the effects of structural features of Pt NPs on the electrochemical performance in the hydrogen evolution reaction (HER). Our approach for the synthesis of metal NPs is distinct in that we produce a "monolayer" of spaced and defined Pt NPs directly on the electrode surface by controlled solid-state dewetting, i.e., by controlled heat-induced agglomeration of thin Pt films into particles [6,7] – see Fig. a. We use magnetron sputtering to deposit Pt films on electrically conductive substrates, followed by thermal treatment in a suitable environment. The resulting NP "monolayers" are tested for electrochemistry without using any binder or ionomer. By varying the duration of the thermal treatment systematically, we observe that dewetted Pt NPs show an evident increase of the ECSA area-specific HER activity compared to as-sputtered films – see Fig. b. This activity trend is consistent in the range of Pt particles’ size investigated (3-60 nm – see size control in Fig. c). The present contribution provides an analysis of the influence of NPs’ features, such as structure, grain size, grain boundaries’ density, and electronic metal-support interaction (EMSI), on the HER activity.In a broader perspective, controlled dewetting allows to precisely tune the properties of metal NPs while at the same reduces the electrode complexity. Advantages are that single-crystalline, well-faceted NPs can be produced on desired electrically conductive substrates (see control of exposed facets in Fig. d). Moreover, dewetted NPs are free from impurities or additives, can be formed with desired composition by tuning the composition of the parent metal film, and can be formed on flat electrode geometries, which is ideal to minimize mass transport limitations and to enable accessibility for spectroscopic techniques.[1] Zhu et al., Chem. Rev. 2020, 120 (2), 851.[2] Lim et al., ACS Catal. 2021, 11 (12), 7568.[3] de Gregorio et al., ACS Catal. 2020, 10 (9), 4854.[4] Feng et al., J. Am. Chem. Soc. 2015, 137 (14), 4606.[5] Zhu et al., Nano Research 2020 13:12 2020, 13 (12), 3310.[6] Thompson, C.V., Annu. Rev. Mater. Res. 2012, 42, 399.[7] Altomare et al., Chem. Sci. 2016, 7 (12), 6865. Figure 1