Facile Synthesis of Co3O4@CoO@Co Gradient Core@Shell Nanoparticles and Their Applications for Oxygen Evolution and Reduction in Alkaline Electrolytes

Abstract

We demonstrate a facile fabrication scheme for Co3O4@CoO@Co (gradient core@shell) nanoparticles on graphene and explore their electrocatalytic potentials for an oxygen evolution reaction (OER) and an oxygen reduction reaction (ORR) in alkaline electrolytes. The synthetic approach begins with the preparation of Co3O4 nanoparticles via a hydrothermal process, which is followed by a controlled hydrogen reduction treatment to render nanoparticles with radial constituents of Co3O4/CoO/Co (inside/outside). X-ray diffraction patterns confirm the formation of crystalline Co3O4 nanoparticles, and their gradual transformation to cubic CoO and fcc Co on the surface. Images from transmission electron microscope reveal a core@shell microstructure. These Co3O4@CoO@Co nanoparticles show impressive activities and durability for OER. For ORR electrocatalysis, the Co3O4@CoO@Co nanoparticles are subjected to a galvanic displacement reaction in which the surface Co atoms undergo oxidative dissolution for the reduction of Pt ions from the electrolyte to form Co3O4@Pt nanoparticles. With commercial Pt/C as a benchmark, we determine the ORR activities in sequence of Pt/C > Co3O4@Pt > Co3O4. Measurements from a rotation disk electrode at various rotation speeds indicate a 4-electron transfer path for Co3O4@Pt. In addition, the specific activity of Co3O4@Pt is more than two times greater than that of Pt/C.

Multifaceted Catalytic ROS‐Scavenging via Electronic Modulated Metal Oxides for Regulating Stem Cell Fate

“…Figure 4b reveals that the MC‐1.0 displays an average Co valence of Co 1.5+ between Co 0 and Co 3+ , indicating there is apparent electron transfer from Mn to Co sites for the Mn‐Co 3 O 4 . [ 42–44 ] As depicted in Figure 4c, Fourier transform analyses of extended X‐ray absorption fine structure (FT‐EXAFS) were used to investigate the coordination environment of Co atoms. MC‐1.0 shows peaks at ≈1.54, 2.43, and 2.96 Å, which are associated with the CoO shell, the nearest CoCo shell, and the remote CoCo shell.…”

Tuning Catalytic Activity of Ni–Co Nanoparticles Synthesized by Gamma‐Radiolytic Reduction of Acetate Aqueous Solutions

“…On the other hand, the Co K HERFD-XAS spectra of the freestanding Co NP do not show a broad structure at ≈7775 eV, characteristic of stoichiometric CoO. [44,45] A dissipation of this structure which rather has the multiple-scattering origin suggests that the formed oxidized Co NPs are highly defective and can be even amorphous. The existence of the Co(II) fraction in the NP samples is also supported by the results of the Co Kβ 1,3 XES measurements (Figure 4c).…”

“…At the same time, the structure at ≈7726 eV grows up and becomes the most intense for the Co/C sample. The latter structure is associated with Co(II) oxide [44,45] and indicates a formation of oxidized NPs, being more significant for the Co/C sample. On the other hand, the Co K HERFD-XAS spectra of the freestanding Co NP do not show a broad structure at ≈7775 eV, characteristic of stoichiometric CoO.…”

Core–shell Fe3O4@CoFe2O4 nanoparticles as high-performance anode catalysts for enhanced oxygen evolution reaction

“…[1][2][3][4] Various approaches have been proposed to enhance their OER activity, notably varying the composition, particle size, and defect concentration, or, recently, forming core-shell structures. [5][6][7][8][9] Owing to their composition-dependent and widely tunable properties, TMOs with spinel structures appear very attractive for various energy-related applications. While Co 3 O 4 and CoOOH thin lms deposited on an Au(111) substrate have demonstrated signicant surface-weighted OER activity, 10 coreshell nanoparticles (NPs) combining a gold core and a TMO shell reached 10 000 A g TM −1 at 1.65 V vs. RHE.…”

“…1–4 Various approaches have been proposed to enhance their OER activity, notably varying the composition, particle size, and defect concentration, or, recently, forming core–shell structures. 5–9…”