The use of ethanol as a fuel in direct alcohol fuel cells depends not only on its ease of production from renewable sources, but also on overcoming the challenges of storage and transportation. In an ethanol‐based fuel cell, highly active electrocatalysts are required to break the C−C bond in ethanol for its complete oxidation at lower overpotentials, with the aim of increasing the cell performance, ethanol conversion rates, and fuel efficiency. In recent decades, the development of wet‐chemistry methods has stimulated research into catalyst design, reactivity tailoring, and mechanistic investigations, and thus, created great opportunities to achieve efficient oxidation of ethanol. In this Minireview, the nanomaterials tested as electrocatalysts for the ethanol oxidation reaction in acid or alkaline environments are summarized. The focus is mainly on nanomaterials synthesized by using wet‐chemistry methods, with particular attention on the relationship between the chemical and physical characteristics of the catalysts, for example, catalyst composition, morphology, structure, degree of alloying, presence of oxides or supports, and their activity for ethanol electro‐oxidation. As potential alternatives to noble metals, non‐noble‐metal catalysts for ethanol oxidation are also briefly reviewed. Insights into further enhancing the catalytic performance through the design of efficient electrocatalysts are also provided.

Materials such as metals, semiconductors, and oxides are attractive at nanometer scales due to the physical and chemical property differences with their bulk counterparts as induced by the quantum confinement effect and large surface-to-volume ratios. In particular, heterogeneous nanostructures consisting of semiconductors and noble metals are extremely important because of the synergistic effects occurring at the interfaces between their noble metal and semiconductor domains; these often equip the heterogeneous nanostructures with improved properties compared to those of isolated individual components. Thus far, heterogeneous nanostructures have garnered a considerable research interest, and tremendous development in achieving high degree control over these nanostructures with respect to their domain size, morphology, and composition has been realized. Their immense application potential in optics, catalysis, imaging, and biomedicine render them a field full of original innovation possibilities. Herein, we demonstrate a phenomenon observed in core-shell nanostructures composed of noble metals and silver sulfide (Ag2S): the inside-out migration of noble metals in Ag2S nanoparticles. We prepare core-shell nanostructures with noble metals and Ag2S residing at the core and shell regions, respectively, through various synthetic strategies including seed-mediated growth and galvanic replacement reactions followed by sulfidation. We then characterize the core-shell nanostructures before and after aging them in toluene at room temperature (e.g. 25 C) for a period of time up to 72 h. In contrast to the reported diffusion of Au from the outside to the inside of InAs or PbTe nanoparticles, which results in an Au core encapsulated by an amorphous InAs or PbTe shell, the noble metals (Au, Ag, Pd, or Pt) in core-shell nanostructures with noble metals and Ag2S residing at the core and shell regions, respectively, are found to diffuse from the inside to the outside through the Ag2S shell. Thus, heterogeneous nanodimers consisting of the corresponding noble metal and Ag2S are formed. Observations using an electron transmission microscope confirm that the inside-out migration of noble metals in Ag2S is carried out in a holistic manner. Due to the apparent interface mismatch between face-centered cubic noble metals and monoclinic Ag2S crystal phases, defects such as vacancies must exist at these interfaces. This makes the migration of noble metals in Ag2S possible by either a vacancy/substitutional mechanism or by the self-purification mechanism that occurs intrinsically in nanoscale semiconductors. As the migration rate of noble metals in Ag2S increases with the decrease in the size of the noble metal core and the radius of noble metal atoms, the inside-out migration rates of Ag, Pd, and Pt in Ag2S are found to be much higher than that of Au because of their smaller particle sizes or atom radii. This scientific phenomenon can be effective in the development of synthetic routes for heterogeneous nanostructures that might not be o...

Preciously tuning the surface composition of noble metal nanoparticles with the particle size of only 2 nm or less by alloying with other metals represents a powerful strategy to boost their electrocatalytic selectivity. However, the synthesis of ultrafine nanoalloys and tuning their surface composition remain challenging. In this report, ultrafine CuPd nanoalloys with the particle size of ca. 2 nm are synthesized based on the galvanic replacement reaction between presynthesized Cu nanoparticles and Pd2+ precursors, and the tuning of their surface compositions is also achieved by changing the atom ratios of Cu/Pd. For the electrocatalytic reduction of CO2, Cu5Pd5 nanoalloys show the CO Faradaic efficiency (FE) of 88% at −0.87 V, and the corresponding mass activity reaches 56 A/g that is much higher than those of Cu8Pd2 nanoalloys, Cu3Pd7 nanoalloys and most of previously reported catalysts. Density functional theory uncovers that with the increase of Pd on the surface of the ultrafine CuPd nanoalloys, the adsorbed energy of both of intermediate COOH* and CO* to the Pd sites is strengthened. The Cu5Pd5 nanoalloys with the optimal surface composition better balance the adsorption of COOH* and desorption of CO*, achieving the highest selectivity and activity. The difficult liberation of absorbed CO* on the surface of Cu3Pd7 nanoalloys provides carbon source to favor the production of ethylene, endowing the Cu3Pd7 nanoalloys with the highest selectivity for ethylene among these ultrafine CuPd nanoalloys.

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