Pt-Free Metal Nanocatalysts for the Oxygen Reduction Reaction Combining Experiment and Theory: An Overview.

The design and manufacture of highly efficient nanocatalysts for the oxygen reduction reaction (ORR) is key to achieve the massive use of proton exchange membrane fuel cells. Up to date, Pt nanocatalysts are widely used for the ORR, but they have various disadvantages such as high cost, limited activity and partial stability. Therefore, different strategies have been implemented to eliminate or reduce the use of Pt in the nanocatalysts for the ORR. Among these, Pt-free metal nanocatalysts have received considerable relevance due to their good catalytic activity and slightly lower cost with respect to Pt. Consequently, nowadays, there are outstanding advances in the design of novel Pt-free metal nanocatalysts for the ORR. In this direction, combining experimental findings and theoretical insights is a low-cost methodology-in terms of both computational cost and laboratory resources-for the design of Pt-free metal nanocatalysts for the ORR in acid media. Therefore, coupled experimental and theoretical investigations are revised and discussed in detail in this review article.

Transformation of Nanostructures Cu2O to Cu3Se2 through Different Routes and the Effect on Photocatalytic Properties.

In this work, copper selenide (Cu3Se2 umangite phase) was synthesized by two routes, using a chemical reaction and the hydrothermal method to obtain CuSe-A and CuSe-H, respectively. The synthesis of Cu3Se2 consisted of a three-step process: in the first step, copper(I) oxide hexapods (Cu2O) were obtained as the copper reservoir; in the second step, selenium ions were obtained from the reduction of selenium powder; and in the third step involves mixing two precursors following the two synthesis routes mentioned before. Analysis of X-ray diffraction and X-ray photoelectron spectroscopy showed the formation of the Cu3Se2 phase by both synthesis routes. On the other hand, using the scanning electron microscopy (SEM) technique, it is observed that the Cu3Se2 sample (CuSe-A) is obtained by exchanging in solution with agitation and that the copper selenium phase grows only on the surface of the hexapods. Meanwhile, the hydrothermal route promotes a total conversion of copper(I) oxide hexapods to the copper selenide phase (CuSe-H). The resulting materials were tested as photocatalytic materials to remove methylene blue dye in water under sunlight irradiation. Cu3Se2 (CuSe-H) obtained by the hydrothermal route exhibited a higher efficiency of photodegradation of dye, reaching a removal percentage of 92% after 4 h under sunlight.