Redox‐Inert Fe³⁺ Ions in Octahedral Sites of Co‐Fe Spinel Oxides with Enhanced Oxygen Catalytic Activity for Rechargeable Zinc–Air Batteries

Abstract

Bimetallic cobalt‐based spinel is sparking much interest, most notably for its excellent bifunctional performance. However, the effect of Fe3+ doping in Co3O4 spinel remains poorly understood, mainly because the surface state of a catalyst is difficult to characterize. Herein, a bifunctional oxygen electrode composed of spinel Co2FeO4/(Co0.72Fe0.28)Td(Co1.28Fe0.72)OctO4 nanoparticles grown on N‐doped carbon nanotubes (NCNTs) is designed, which exhibits superior performance to state‐of‐the‐art noble metal catalysts. Theoretical calculations and magnetic measurements reveal that the introduction of Fe3+ ions into the Co3O4 network causes delocalization of the Co 3d electrons and spin‐state transition. Fe3+ ions can effectively activate adjacent Co3+ ions under the action of both spin and charge effect, resulting in the enhanced intrinsic oxygen catalytic activity of the hybrid spinel Co2FeO4. This work provides not only a promising bifunctional electrode for zinc–air batteries, but also offers a new insight to understand the Co‐Fe spinel oxides for oxygen electrocatalysis.

Dual Role of Silver Moieties Coupled with Ordered Mesoporous Cobalt Oxide towards Electrocatalytic Oxygen Evolution Reaction

“…[54,63,64] Another possible reason is the presence of Fe 3+ stimulating the oxidation of M 2+ (M:Coand Ni)toM 3+/4+ instead of its further oxidation to Fe 4+ . [56,57,65] As seen in Figure S23, the Ag 2 Oitself showed avery poor OER activity even in the presence of an excess amount of iron impurity.Therefore,itdoes make sense to postulate either (i) the interaction between Ag 2 Oa dsorbed by iron impurities and Co 3 O 4 or (ii)t he formation of new active species consisting of cobalt-silver-iron synergistically facilitated the OER kinetics.R esultantly,m uch higher current density at 1.7 V RHE was achieved on the activated Co 8 Ag oxide (211 mA cm À2 ), more than twice of that of Co 3 O 4 (102 mA cm À2 ). Even compared with the recent-reported benchmarked cobalt electrocatalysts,C o 8 Ag oxide displayed competitive catalytic performance,a slisted in Table S2.…”

“…In Co-based electrocatalytic systems,ithas been proposed that the formation of active species could be ascribed by (i) Fe-modified Co sites, [56,57] (ii)F es pecies with ah igh-valent oxidation state, [51,54] and (iii)c oordinated Co-Fem oiety. [52] Although it is still controversial, there is no doubt that the efficient uptake of Fe impurities is essential to activate Cobased electrocatalysts for OER.…”

Dual Role of Silver Moieties Coupled with Ordered Mesoporous Cobalt Oxide towards Electrocatalytic Oxygen Evolution Reaction

“…[54,63,64] Another possible reason is the presence of Fe 3+ stimulating the oxidation of M 2+ (M:Coand Ni)toM 3+/4+ instead of its further oxidation to Fe 4+ . [56,57,65] As seen in Figure S23, the Ag 2 Oitself showed avery poor OER activity even in the presence of an excess amount of iron impurity.Therefore,itdoes make sense to postulate either (i)…”

Microwave-assisted pyrolysis of Pachira aquatica leaves as a catalyst for the oxygen reduction reaction

“…Wang et al used Fe 3+ doped Co 3 O 4 to form the octahedral Co-Fe spinel oxides and grew it on N-doped carbon nanotubes as a bifunctional electrode for zinc-air batteries. 26 According to the structural characterization and theoretical calculation, the obtained catalyst had the effect of spin and charge, resulting in the enhanced oxygen catalytic activity. Additionally, transition metal catalyst-based materials as a non-precious metal catalyst in AAEMFC have been developed in our previous studies.…”