Co₃O₄@(Fe-Doped)Co(OH)₂ Microfibers: Facile Synthesis, Oriented-Assembly, Formation Mechanism, and High Electrocatalytic Activity

Cobalt oxide or hydroxide nanoarchitectures, often synthesized via solvothermal or electrodeposition or templated approaches, have wide technological applications owing to their inherent electrochemical activity and unique magnetic responsive properties. Herein, by revisiting the well-studied aqueous system of Co/NaBH₄ at room temperature, the chainlike assembly of Co₃O₄ nanoparticles is attained with the assistance of an external magnetic field; more importantly, a one-dimensional hierarchical array consisting of perpendicularly oriented and interconnected Co­(OH)₂ thin nanosheets could be constructed upon such well-aligned Co₃O₄ assembly, generating biphasic core–shell-structured Co₃O₄@Co­(OH)₂ microfibers with permanent structural integrity even upon the removal of the external magnetic field; isomorphous doping was also introduced to produce Co₃O₄@Fe–Co­(OH)₂ microfibers with similar structural merits. The cobalt-chemistry in such a Co/NaBH₄ aqueous system was illustrated to reveal the compositional and morphological evolutions of the cobalt species and the formation mechanism of the microfibers. Owing to the presence of Co₃O₄ as the core, such anisotropic Co₃O₄@(Fe-doped)­Co­(OH)₂ microfibers demonstrated interesting magnetic-responsive behaviors, which could undergo macro-scale oriented-assembly in response to a magnetic stimulus; and with the presence of a hierarchical array of weakly crystallized thin (Fe-doped) Co­(OH)₂ nanosheets with polycrystallinity as the shell, such microfibers demonstrated remarkable electrocatalytic activity toward oxygen evolution reactions in alkaline conditions

One-Pot Synthesis of Ternary Pt–Ni–Cu Nanocrystals with High Catalytic Performance

Shape-controlled synthesis of multicomponent metal nanocrystals (NCs) bounded by high-index facets (HIFs) is of significant importance in the design and synthesis of highly active catalysts. It is a highly challenging task to design and synthesize ternary alloy NCs with HIFs due to the formidable difficulties in controlling the nucleation/growth kinetics of NCs in the presence of three metal precursors with different reduction potentials. We report herein, for the first time, the preparation of Pt–Ni–Cu alloy NCs by tuning their shape from crossed, dendritic, concave nanocubic (CNC) to rough octahedral (ROH) NCs through a facile one-pot solvothermal synthesis method. Specifically, the crossed and CNC Pt–Ni–Cu alloy NCs are bounded by high-index {<i>hk</i>0} facets and ROH with rich lattice defects. The electrocatalytic activities of these Pt–Ni–Cu alloy NCs toward methanol and formic acid oxidation were tested. It was shown that these Pt–Ni–Cu alloy NCs exhibited enhanced activity and stability compared to commercial Pt black and Pt/C catalysts as well as previous Pt–Ni and Pt CNCs under the same reaction conditions, demonstrating the superior electrocatalytic activity of Pt–Ni–Cu ternary alloys compared to monometal and binary Pt–Ni NCs. Surprisingly, we have found that the Pt–Ni–Cu ROH NCs have exhibited a higher specific catalytic activity than the crossed and CNC Pt–Ni–Cu alloy NCs with HIFs. The electronic and structure effects have been extensively discussed to shed light on the excellent electrocatalytic performance of Pt–Ni–Cu ROH NCs