Transformation of Co₃O₄nanoparticles to CoO monitored byin situTEM and predicted ferromagnetism at the Co₃O₄/CoO interface from first principles

Abstract

Nanoparticles of Co3O4 and CoO are of paramount importance because of their chemical properties propelling their applications in catalysis and battery materials, and because of their intriguing magnetic properties. Here...

Thermally driven phase transition of cobalt hydroxide sheets via cobalt oxides to cobalt nanoparticles

“…[14][15][16] Cobalt oxides, representative TMOs, are a family of chemical compounds consisting of cobalt and oxygen atoms, which can exist in various stoichiometries. [17][18][19][20][21] Cobalt oxide catalyzes the oxygen evolution reaction, and two-dimensional (2D) cobalt hydroxide (Co(OH) 2 ), cobalt oxyhydroxide (CoOOH), and cobalt oxide are more efficient catalysts than their bulk counterparts. [23][24][25][26][27] Therefore, recent research is focused on the preparation of 2D cobalt oxide nanosheets with non-layered or layered structures using methods such as hydrothermal reaction, 28,29 electrodeposition, 30,31 atomic layer deposition, 32,33 and ionic layer epitaxy.…”

“…[23][24][25][26][27] Therefore, recent research is focused on the preparation of 2D cobalt oxide nanosheets with non-layered or layered structures using methods such as hydrothermal reaction, 28,29 electrodeposition, 30,31 atomic layer deposition, 32,33 and ionic layer epitaxy. 34 The commonly investigated phases of cobalt oxide are spinel Co 3 O 4 , hexagonal CoO (h-CoO), and cubic CoO (c-CoO), [17][18][19][20][21][22] all of which undergo phase transformations under certain conditions. 18,20 The synthesis and use of the stable phases of the cobalt oxides have received considerable attention in recent years, 35,36 and interesting studies have been reported on the thermodynamic behaviors of phase transitions.…”

“…34 The commonly investigated phases of cobalt oxide are spinel Co 3 O 4 , hexagonal CoO (h-CoO), and cubic CoO (c-CoO), [17][18][19][20][21][22] all of which undergo phase transformations under certain conditions. 18,20 The synthesis and use of the stable phases of the cobalt oxides have received considerable attention in recent years, 35,36 and interesting studies have been reported on the thermodynamic behaviors of phase transitions. 17,18,20 However, studies on phase transformations originating from cobalt hydroxide are lacking.…”

“…18,20 The synthesis and use of the stable phases of the cobalt oxides have received considerable attention in recent years, 35,36 and interesting studies have been reported on the thermodynamic behaviors of phase transitions. 17,18,20 However, studies on phase transformations originating from cobalt hydroxide are lacking. The stoichiometric ratio of synthetic cobalt oxide (transition metal ion to oxygen ion) with a non-layered structure is 1 : 1 or 3 : 4, while that of synthesized Co(OH) 2 nanosheets with a layered structure is 1 : 2.…”

“…Since it is possible to understand the process of forming different crystalline structures of a hexagonal lattice, it is possible to systematically confirm the implementation of multiple intermediate phases. 20 Various phases of cobalt oxide are formed because of the structural changes induced by oxygen loss. The Co 3 O 4 structure appears within a specific temperature range, and the continuous increase in temperature induces a final structural change leading to the formation of Co nanoparticles.…”