Electrocatalysis on shape-controlled metal nanoparticles: Progress in surface cleaning methodologies

Abstract

The use of shape-controlled metal nanoparticles has produced not only a clear enhancement in the electrocatalytic activity of different reactions of interest but also a better understanding of the effect of the surface structure on nanoscaled materials. However, it is well-accepted that a correct understanding of the correlations between shape/surface structure and electrochemical reactivity indispensably requires the use of clean surfaces. In this regard, and considering that most of the synthetic methodologies available in the literature for the preparation of these shaped metal nanoparticles employ capping agents, the development of effective surface cleaning methodologies able to remove such capping agents from the surface of the corresponding nanoparticles, becomes an extremely important prerequisite to subsequently evaluate their electrocatalytic properties for any reaction of interest.Consequently, in this contribution, we summarize the most relevant advances about surface cleaning procedures applied to different shaped metal nanoparticles for electrocatalytic purposes. It is worth mentioning that this work will only include contributions in which the surface cleanness of the samples is specifically evaluated using well-established electrochemical tools.

Controlled Synthesis of Surfactant‐Free Water‐Dispersible Colloidal Platinum Nanoparticles by the Co4Cat Process

“…From a research and development point of view, the use of additives is equally disadvantageous: it complicates systematic studies and a thorough testing of hypotheses by adding steps and uncertainties. Common procedures to remove additives are UV‐irradiation as well as harsh thermal or chemical treatments, which can impair the composition and structure of the as‐prepared NPs and may result in limited reproducibility and scalability …”

“…[23] Their removal, for instance, is key in electrochemistry and related energy applications, [15,24] in which fully accessible surfacesf or electron transfer are necessary.F rom a research and development point of view,t he use of additives is equally disadvantageous:i tc omplicates systematic studies and at horough testing of hypotheses by addings teps and uncertainties. Common procedurest or emove additives are UV-irradiationa sw ell as harsh thermalo rc hemical treatments, [25] which can impair the compositiona nd structure of the as-prepared NPs and may result in limited reproducibility and scalability. [23a] Recent examples support the benefits of surfactant-free syntheses.U nprotected or weakly protected NPs reachc ompetitive catalytic efficiency compared to the state-of-the-art, [26] such as, for instance, Pd NPs prepared in methanol for acetylene hydrogenation [27] and dehydrogenation of formic acid.…”

Dissolution of Platinum Single Crystals in Acidic Medium

“…In the quest to improve electrocatalyst activity towards the oxygen reduction reaction (ORR) and reduce the required quantities of platinum in the CL, one promising strategy is the use of platinum and platinum alloy nanoparticles with preferential shapes exposing the low index face-centered cubic crystal facets. [19][20][21][22][23][24][25][26][27] Although activity trends have been identified among the varied shapes and exposed facets, reaching firm conclusions has required the development of techniques to produced very clean surfaces. These difficulties highlight the need for well-defined systems in a bottom up approach to understanding electrocatalysis.…”

Citrate-Coated, Size-Tunable Octahedral Platinum Nanocrystals: A Novel Route for Advanced Electrocatalysts

“…the specific arrangement of the atoms at the surface, is the key point determining and controlling the electrocatalytic properties of the material. 13,[22][23][24] Many synthetic strategies have been proposed to obtain shaped Pt nanocrystals, particularly focusing on wet chemical reaction methods. The main parameter is typically the stabilization of a facet through the use of additives.…”

“…27 4 Moreover, a recent contribution reviews the most relevant advances dealing with efficient surface cleaning methodologies applied to shape-controlled metal nanoparticles, showing the challenges associated with this process. 22 On the other hand, it is well-accepted that, as the particle size decreases, the proportion of {111} and {100} domains tends to decrease dramatically, while low coordination sites such as edges, steps, corners and kinks become predominant in the surface. 28 Consequently, the possibility of designing few nanometer size octahedral Pt nanocrystals with high percentage of {111} facet percentage represents a challenge.…”