The oxidation of ammonia on platinum surfaces is a structure sensitive reaction that takes place almost exclusively on Pt(100) sites. This report shows how dependent the activity is on different arrangements of (100) sites of platinum. The effect of two-dimensional domains has been addressed by using stepped surfaces having terraces with (100) geometry, either with (111) and (110) steps. The results were compared with those obtained from stepped surfaces having terraces with (111) or (110) symmetry and monatomic (100) steps, thus representing monodimensional (100) domains. The observed behavior confirms the extreme sensitivity of the reaction to the different arrangement of this type of square sites.

In situ Raman spectra have been obtained for different species (CN -, CO, H) adsorbed on nanostructured electrodes prepared by deposition of pure Pt and Pd nanoparticles (around 4 nm in size) on either gold or platinum electrodes in acidic solutions. The surface enhancement factor has been estimated on the basis of cyanide spectra obtained both at the surface and in solution. It attains a value as high as 550, around 3-4 times higher than that reported for roughened Pt electrodes for the same adsorbate. In the case of CO, typical bands for the stretching of the Pt/Pd-C and C-O bonds have been observed for low acquisition times (ca. 1 s), evidencing that pure Pt and Pd nanoparticles sustain significant surface enhancement effects. The spectra show mainly atop CO coordination for Pt nanoparticles whereas both linear and bridge CO are detected for Pd nanoparticles. The potential advantages of the nanoparticle-on-electrode approach in Raman spectroelectrochemical studies are highlighted.

Ethanol oxidation on different shape-controlled platinum nanoparticles at different pHs was studied using electrochemical, Attenuated Total Reflection -Fourier Transform Infrared Spectroscopy (ATR-FTIR) and, especially, Differential Electrochemical Mass Spectrometry (DEMS) techniques, which gives interesting quantitative information about the products of ethanol oxidation. Two Pt nanoparticle samples were used for this purpose: (100) and (111) preferentially oriented Pt nanoparticles. The results are in agreement with previous findings that the preferred decomposition product depends on surface structure, with COads formation on (100) domains and acetaldehyde/acetic acid formation on (111) domains. However, new information has been obtained about the changes in CHx and CO formation at lower potentials when the pH is changed, showing that CHx formation is favored against the decrease in CO adsorption on (100) domains. At higher potentials, complete oxidation to CO2 occurs from both CHx and CO fragments. In (111) Pt nanoparticles, the splitting of C-C bond is hindered, favoring acetaldehyde and acetate formation even in 0.5 M H2SO4. C1 fragments become even less when the pH increases, being nearly negligible in the highest pH studied.

Electrocatalysis is at the heart of a broad range of physicochemical applications that play an important role in the present and future of a sustainable economy. Among the myriad of different electrocatalysts used in this field, nanomaterials are of ubiquitous importance. An increased surface area/volume ratio compared to bulk makes nanoscale catalysts the preferred choice to perform electrocatalytic reactions. Bragg coherent diffraction imaging (BCDI) was introduced in 2006 and since has been applied to obtain 3D images of crystalline nanomaterials. BCDI provides information about the displacement field, which is directly related to strain. Lattice strain in the catalysts impacts their electronic configuration and, consequently, their binding energy with reaction intermediates. Even though there have been significant improvements since its birth, the fact that the experiments can only be performed at synchrotron facilities and its relatively low resolution to date (∼10 nm spatial resolution) have prevented the popularization of this technique. Herein, we will briefly describe the fundamentals of the technique, including the electrocatalysis relevant information that we can extract from it. Subsequently, we review some of the computational experiments that complement the BCDI data for enhanced information extraction and improved understanding of the underlying nanoscale electrocatalytic processes. We next highlight success stories of BCDI applied to different electrochemical systems and in heterogeneous catalysis to show how the technique can contribute to future studies in electrocatalysis. Finally, we outline current challenges in spatiotemporal resolution limits of BCDI and provide our perspectives on recent developments in synchrotron facilities as well as the role of machine learning and artificial intelligence in addressing them.

Pd nanocrystals were produced with uniform truncated‐cube shape and a narrow size distribution, yielding controlled surface area fractions from low Miller index ({100}, {110}, {111}) crystalline facets. Details on the structure and morphology of the nanocrystals were obtained by combining X‐ray powder diffraction line profile analysis, high‐resolution transmission electron microscopy and surface electrochemistry based on Cu underpotential deposition.

The electron induced damage in self-assembled monolayers (SAMs) of n-dodecanethiolate on Au(111) and Au(100) single-crystalline surfaces is investigated in situ by X-ray photoelectron spectroscopy. The same irradiation dose produced different adsorbed groups. The damage at the headgroup-substrate interface leads to find dialkyl sulfide (RS-R') on Au(111), while dialkyl disulfide (RS-SR) and/or thiol (RSH) were produced on Au(100). With regards to C species, significant amounts of C=C are generated on Au(111) but not on Au(100), showing that the double bond formation is not triggered through the same pathways on these surfaces. A detailed analysis of a variety of mechanisms, which involved cationic (RS + ), anionic (RS − ) or thiyl radical (RS • ) species, in combination with ab-initio DFT calculation leads to the conclusion that the radical pathways successfully explain the experimental results. Molecular dynamics simulations show that the n-dodecanethiolate-SAMs on both surfaces are equivalent with regard to the van der Waals interactions. The breakage of the S-Au bonds is studied by means of DFT calculations. The thiyl radical would form close to the Au(100) surface, making it likely to react with another thiyl radical or thiolate to form the RS-SR species. On the other hand, for Au(111) the thiyl radical would form farther from the surface, reacting with the alkyl chains of neighboring molecules to form RS-R' species. The mechanistic framework here proposed is very useful to explain the behavior of related systems.

Thallium modified shape-controlled Pt nanoparticles were prepared and their electrocatalytic activity towards formic acid electrooxidation was evaluated in 0.5 M sulfuric acid. The electrochemical and in situ FTIR spectroscopic results show a remarkable improvement in the electrocatalytic activity, especially in the low potential region (around 0.1-0.2 V vs. RHE). Cubic Pt nanoparticles modified with Tl were found to be more active than the octahedral Pt ones in the entire range of Tl coverages and potential windows. In situ FTIR spectra indicate that the promotional effect produced by Tl results in the inhibition of the poisoning step leading to COads, thus improving the onset potential for the complete formic acid oxidation to CO2. Chronoamperometric experiments were also performed at 0.2 V to evaluate the stability of the electrocatalysts at constant potential. Finally, experiments with different concentrations of formic acid (0.05-1 M) were also carried out. In all cases, Tl-modified cubic Pt nanoparticles result to be the most active. All these facts reinforce the importance of controlling the surface structure of the electrocatalysts to optimize their electrocatalytic properties.

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