Deema Balalta

Controlling the interplay between reduction and galvanic processes is critical for tailoring the structure and composition of multimetallic nanocrystals. Here, we report a synthetic strategy to produce anisotropic Au–Pd–Pt nanocrystals with tunable morphologies and elemental distributions. Platinum deposition on single-crystal Au@Pd nanorods (NRs) was modulated by varying the concentration of ascorbic acid, enabling control over the balance between reduction and galvanic-like processes. This approach yields distinct nanostructures, including nanoframes, cloud-like morphologies, and core–shell–shell architectures. Advanced electron microscopy, including high-resolution HAADF STEM imaging, EDX elemental mapping, and electron tomography, reveals intricate elemental distributions, the formation of cavities and tunnels, the apparent preservation of single-crystal characteristics in Au@Pd NRs under the explored conditions, and gold etching induced by the platinum precursor. A preliminary evaluation of catalytic activity suggests enhanced ethanol oxidation performance for nanoframe structures. These findings establish a versatile strategy for engineering anisotropic multimetallic nanocrystals through controlled redox interplay.

The electrochemical reduction of carbon dioxide (or the CO₂-reduction reaction, CO₂RR) presents a promising strategy to mitigate CO₂ emissions while producing valuable chemical feedstocks. Palladium (Pd) catalysts are particularly interesting for their capacity to selectively produce formate at low overpotentials and carbon monoxide (CO) at higher overpotentials. However, palladium’s CO₂-to-formate activity is often hindered by the progressive poisoning of its surface with CO. To shed light on the parameters that control this performance-determining process, in this study we employ Operando grazing incidence X-ray absorption spectroscopy and attenuated total reflectance surface-enhanced infrared absorption spectroscopy to investigate the CO₂RR mechanism on carbon-supported Pd nanoparticles (Pd/C) and a freestanding Pd aerogel with similar electrochemical surface areas but substantial differences in hydride formation, CO poisoning, and catalytic performance. Pd/C demonstrates rapid hydride formation and constant formate activity at −100 and −200 mV vs the reversible hydrogen electrode, revealing an indirect correlation between activity for formate and hydride stoichiometry that strongly indicates the active involvement of the surface hydride in the CO₂RR to formate. In contrast, the Pd aerogel suffers from rapid CO surface poisoning and a concomitantly negligible formate-production activity at the same potentials. These differences in catalytic behavior are linked to an increased presence of grain boundaries in the aerogel’s surface that has been tied to a reduction in the activation barrier for CO₂ conversion to the surface-adsorbed *COOH and the subsequent formation of strongly adsorbed CO. As such, our findings highlight how optimizing the structural features of Pd-based surfaces can lead to significant enhancements in their efficiency toward formate production.

Sequential chemical and electrochemical activation induces controlled restructuring of Cu_2−xSe nanowires, yielding phase-separated architectures that modulate CO₂RR selectivity.

Anodization induced nanostructuring of copper surfaces facilitates CO ₂ electroreduction to C ₂₊ products.

The electrochemical reduction of CO₂ is a promising approach to mitigate global warming by converting CO₂ into valuable industrial chemicals such as CO. Among the various CO₂-electroreduction catalysts investigated, AuCu alloys have proven to be particularly promising as they exhibit even higher activity and selectivity toward CO production compared to pure Au, which can be considered as one of the state-of-the-art catalysts for this reaction. In a recent study, we showed that unsupported AuCu aerogels feature an appealing CO₂-to-CO activity and selectivity, even if in their as-synthesized form they were not phase-pure but instead contained Cu oxide. Thus, in this work, we aim at understanding how the transformation of this bimetallic and compositionally heterogeneous aerogel induced by a cyclic voltammetry (CV) treatment leads to this enhanced CO₂-electroreduction performance. This was done by applying three different experimental protocols, implying (i) the absence of this CV treatment, (ii) the completion of the CV treatment without exchanging the electrolyte prior to the CO₂-reduction test, or (iii) the CV treatment and exchanging the electrolyte before performing the CO₂-reduction potential hold. These three protocols were complemented with operando grazing incidence X-ray absorption spectroscopy (GIXAS) measurements that revealed the structural and compositional changes undergone by the AuCu aerogel during CV treatment. The latter is then shown to lead to the removal of Cu oxide side phases and the enrichment of the aerogel's surface with Au atoms and a AuCu alloy phase, which in turn results in a significant increase in the faradaic efficiency toward CO, from 23 to 81% when this CV treatment is overlooked vs performed, respectively.