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CO2reduction reaction (CO2RR) facilitates the sustainable synthesis of fuels and chemicals. Although copper (Cu) enables CO2-to-multicarbon product (C2+) conversion, Cu-based electrocatalysts, particularly nanocatalysts, face challenges in poor selectivity and stability owing to the highly dynamic nature of Cu atoms under reaction conditions. Core–shell structures present a promising approach to address these issues by modulating the Cu overlayer–substrate interactions with atomic-level precision. Here, we report on Pd@Cu core–shell structures with atomically thin and nanometer-thick Cu overlayers on single-crystal Pd nanocubes with {100} facets promoting the CO2-to-C2+conversion. The microstructures and surface compositions at the atomically sharp Pd/Cu interface were investigated by atomic-scale scanning transmission electron microscopy (STEM) imaging and electron energy-loss spectroscopy (EELS). Our results reveal that atomic-layer Cu epitaxially grows on Pd and adapts to the lattice of the Pd substrate. The reaction-driven migration of atomic-layer Cu is effectively suppressed on Pd due to the strong Cu–Pd interaction. While Pd only reduces CO2to C1products, atomic-layer Cu on Pd can initiate the C2+production during the CO2RR. Thick Cu overlayers (∼15 nm) on Pd further enhance the C2+faradaic efficiency while undergoing significant structural reconstruction, with only the 2–3 nm Cu layers near the Pd surface remaining stable and resistant to Cu migration after the CO2RR. We anticipate that Pd@Cu core–shell structures with intermediate Cu shell thickness hold significant potential for enhancing C2+selectivity while maintaining high stability of nanocatalysts for CO2reduction to liquid fuels.

Modification of electrocatalysts with ionic liquids (ILs) allows us to control the activity and selectivity on the one hand but also directly affects the stability of the electrode. In this work, we studied the interaction of the IL 1-ethyl-3-methylimidazolium dicyanamide [C2C1Im][DCA] with a Au(111) surface in an aqueous electrolyte (phosphate buffer, pH 7) and the impact of the IL on the electrochemical stability of the surface. We combined complementary electrochemical in situ methods, namely, electrochemical infrared reflection absorption spectroscopy (EC-IRRAS), cyclic voltammetry (CV), electrochemical scanning tunneling microscopy (EC-STM), and online inductively coupled plasma mass spectrometry. We observe the potential-dependent and reversible adsorption–desorption of ionic species on the Au(111) surface in the potential window between 0.1 and 1.1 VRHE. We identified two types of adsorbed [DCA]−species, showing different adsorption kinetics. Already at low concentrations, the IL (10 mM) enhances the dissolution during oxidation and reduction cycles by a factor of more than 40. We observe a suppressed redeposition of dissolved Au-ions in the presence of the IL due to the formation of gold complexes with the [DCA]−anions. Our result provides molecular insights into the interplay between ionic liquid–surface interactions and surface stability.

The most recent advances for the ORR in Pt single crystal electrodes are summarized. A mechanism for the reaction is presented in light of the recent results.

The study of the oxygen reduction reaction (ORR) at high-index Pt(hkl) single crystal surfaces has received considerable interest due to their well-ordered, typical atomic structures and superior catalytic activities. However, it is difficult to obtain direct spectral evidence of ORR intermediates during reaction processes, especially at high-index Pt(hkl) surfaces. Herein, in situRaman spectroscopy has been employed to investigate ORR processes at high-index Pt(hkl) surfaces containing the [011̅] crystal zone—i.e., Pt(211) and Pt(311). Through control and isotope substitution experiments, in situspectroscopic evidence of OH and OOH intermediates at Pt(211) and Pt(311) surfaces was successfully obtained. After detailed analysis based on the Raman spectra and theoretical simulation, it was deduced that the difference in adsorption of OOH at high-index surfaces has a significant effect on the ORR activity. This research illuminates and deepens the understanding of the ORR mechanism on high-index Pt(hkl) surfaces and provides theoretical guidance for the rational design of high activity ORR catalysts.

Bromide adsorption on Pt(111) is investigated by means of cyclic voltammetry and CO displacement experiments at different pH values. In acidic pH, bromide adsorption is strongly overlapped with hydrogen desorption process. However, as the pH increases, hydrogen adsorption process displaces toward negative potentials while bromide adsorption remains nearly in the same potential region. In consequence, both processes decouple at higher pH values. The structural transition from Pt(111)-(1×1) to Pt(111)(3×3)-4Br is pH independent, in the SHE scale, and not observed for pH > 9.1. Values of pztc are extracted from the combination of voltammetric and CO displaced charges. An alternative approach to obtain charge curves is based on the coincidence of the curves at the structural transition characteristic of the bromide adlayer completion. Pztc values obtained from different approaches with and without bromide are compared, and their dependence on pH discussed. A thermodynamic analysis is carried out to obtain hydrogen Gibbs excess and charge number from the Esin Markov analysis.

The interface between the Pt(111) surface and several MeF/HClO4(Me+= Li+, Na+, or Cs+) aqueous electrolytes is investigated by means of cyclic voltammetry and laser-induced temperature jump experiments. Results point out that the effect of the electrolyte on the interfacial water structure is different depending on the nature of the metal alkali cation, with the values of the potential of maximum entropy (pme) following the order pme (Li+) < pme (Na+) < pme (Cs+). In addition, the hydrogen peroxide reduction reaction is studied under these conditions. This reaction is inhibited at low potentials as a consequence of the build up of negative charges on the electrode surface. The potential where this inhibition takes place (Einhibition) follows the same trend as the pme. These results evidence that the activity of an electrocatalytic reaction can depend to great extent on the structure of the interfacial water adlayer and that the latter can be modulated by the nature of the alkali metal cation.

No relevant conflicts of interest to declare.