Self-Composition of Hierarchical Core–Shell-Structured NiCo₂O₄@NiCo₂O₄ Microspheres with Oxygen Vacancies for Efficient Oxygen Evolution Electrocatalysis

Abstract

The reactivity of oxygen evolution reaction (OER) electrocatalysts can be effectively controlled by the subtle design of their morphologies, composition, and surface defects. Herein, the hierarchical core−shell-structured NiCo 2 O 4 @NiCo 2 O 4 microspheres (NCO-2) are synthesized by a "self-composition" strategy in the onepot hydrothermal process followed by calcination. The unique nanoarchitecture of NCO-2 has NiCo 2 O 4 solid microspheres as the core and ultrathin porous NiCo 2 O 4 nanosheets as the shell, acting synergistically with the surface oxygen vacancies, which can afford more efficient active sites and shorten the transportation/diffusion path for electrons and electrolyte ions, thus evidently optimizing the OER kinetics. Consequently, the obtained NCO-2 exhibits significant electrocatalytic activity with a low overpotential of ∼350 mV and long-term stability of 30 h at 10 mA cm −2 in a 1.0 M KOH electrolyte, which outperforms those of NiCo 2 O 4 with diverse morphologies (solid sphere, urchin-like, and hollow structures) and commercial IrO 2 . This approach provides a promising route to design intricate catalyst structures for OER applications.

2023 Pioneers in Energy Research: Shizhang Qiao

“…The reactivity of OER electrocatalysts can be effectively controlled by the subtle design of their morphologies, composition, and surface defects. For this purpose, Zhao et al synthesized hierarchical core–shell-structured NiCo 2 O 4 @NiCo 2 O 4 microspheres. The obtained catalysts exhibit significant electrocatalytic activity with a low overpotential and long-term stability, and they outperform NiCo 2 O 4 with diverse morphologies (solid sphere, urchin-like, and hollow structures) and commercial IrO 2 .…”

Oxygen Vacancy‐Rich NiCo2O4 on Carbon Framework with Controlled Pore Architectures as Efficient Bifunctional Electrocatalysts for Zn‐Air Batteries

“…Pore size modulation, including micro-, meso-, and macropores, can facilitate the electrocatalytic activity by regulating the crystal size to expose sufficient active sites, promote mass transport, and facilitate the detachment of the O 2 bubbleblocking surface of the active site [8,[39][40][41]. Among the various TMOs, NiCo 2 O 4 (NCO), which is a spinel oxide with Ni ions occupying octahedral sites in the Co 3 O 4 lattice, has attracted significant attention as an electrocatalyst owing to its availability and stability [42][43][44][45]. Yuan et al reported the superior ORR activity of NCO nanosheets on hollow mesoporous carbon with oxygen vacancies through an annealing treatment in a low-oxygen atmosphere [46].…”