Controllable Fabrication of Transition Metal-Based Nanohybrids for Enhanced Electrochemical Catalytic Performances

Abstract

This thesis describes the controllable fabrication of transition metal-based nanohybrids for enhanced electrochemical catalytic performances. First, bimetallic nanoparticles comprising a gold multipod nanoparticle (GMN) core and distinctive Pd shell (GMN@Pd NPs) are successfully synthesized in a facile and controllable manner. Epitaxial or islanded growth of Pd on the GMNs can be readily achieved using appropriate stabilizing agents. The controllable growth mode of the Pd layers, coupled with the unique topologies of GMNs, are advantageous for enhancing the density of active interfacial surfaces in the composites. Particularly, I-GMN@Pd NPs show substantially enhanced ORR activity compared with monometallic counterparts and excellent durability and better tolerance to the crossover effect than that of Pt/C, rendering the materials highly desirable for practical use. Second, a successful synthesis of Ni(OH)2 nanoflowers with a high degree of crystallinity and uniformity was reported. The as-prepared Ni(OH)2 nanoflowers are employed as templates for effective and controllable loading of Au nanodots to obtain Ni(OH)2@Au nanohybrids. An examination of the OER activity reveals that Ni(OH)2@Au exhibits a considerably lower overpotential value (390 mV) at a current density of 5 mA/cm2 and a smaller Tafel slope (120 mV/dec) than those of Ni(OH)2 (540 mV and 324 mV/dec, respectively). The OER enhancement effect is mainly attributed to the decoration of Au nanoparticles, inducing charge transfer from Ni to Au and thereby stabilizing the Ni species at high oxidation levels. Moreover, the uniform loading of Au nanodots on the anisotropic Ni(OH)2 nanoflowers provides more active interfacial surfaces, which are expedient to OER. Third, nickel/iron hydroxide nanohybrids and nickel/iron/selenide nanohybrids were successfully synthesized on selected substrates such as graphite and nickel foil. In particular, nickel/iron/selenide nanohybrids on nickel foil (NF-[NiFeSe]) exhibit substantially enhanced OER catalytic activity with low overpotential and Tafel slope values, as well as pliability. The use of nickel foil and direct growth of heterostructured nickel/iron/selenide nanohybrids can be employed to effectively and economically design high-performance water-splitting devices.