Spindle Spinel CoFeCoO₄ Microparticles/rGO as an Oxygen Reduction and Oxygen Evolution Catalyst

Abstract

The representative spinel-type materials AB2O4 (both A and B are transition metals) electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have been investigated and significant improvements have been achieved in the activity and durability for ORR and OER in the alkaline solution. But CoFeCoO4 was not explored widely like ZnCo2O4 (or NiCo2O[Formula: see text] as the ORR electrocatalyst for its relatively complicated atomic site occupation. CoFeCoO4 has a typical cubic spinel structure with Co[Formula: see text] in the tetrahedron and Co[Formula: see text] and Fe[Formula: see text] in the octahedron. A mixture of Co[Formula: see text] and Fe[Formula: see text] in the B site makes the oxide have a wider overlap between transition metal 3d orbit and O 2p orbit, which can lead to an effective charge transfer in the rate-determining steps of ORR process and then enhance the ORR activity. The high electronic conductivity and specific surface area of rGO can accelerate charger transfer and provide more catalytic sites, which would contribute to a faster ORR process. In this work, the porous spindle CoFeCoO4 microparticles which were synthesized by hydrothermal technology, were assembled on the rGO surface to obtain the CoFeCoO4/rGO composite, which exhibited enhanced ORR activity and catalytic stability comparable to that of Pt/C. On the other hand, the OER catalytic activity of the prepared samples was also studied to explore the potential of CoFeCoO4/rGO as a bifunctional oxygen catalyst.

Reduced graphene oxide‐based materials for electrochemical energy conversion reactions

“…Ternary ceramic oxides combined with rGO have been used as catalytic materials for ORR. 150,161,162 The ternary ceramic oxides/rGO composite catalysts not only promote the interfacial electron transfer but also improve the ORR performance. Yu et al 151 reported the highly efficient ORR catalytic activities with SmMn 2 O 5 @NrGO hybrid nanocomposites.…”

“…The excellent catalytic activity is ascribed to the hierarchical structure of porous Co-ZnO NPs, offering larger surface area and efficient utilization of catalytic active sites. Ternary ceramic oxides combined with rGO have been used as catalytic materials for ORR 150,161,162. The ternary ceramic oxides/rGO composite catalysts not only promote the interfacial electron transfer but also improve the ORR performance.…”

Beads‐on‐string hierarchical structured electrocatalysts for efficient oxygen reduction reaction

“…As shown in Figure 4D, NH 3 –Ag@C@Co–N–C‐700 shows a high Brunauer–Emmett–Teller surface area of 277.5 m 2 /g, which is larger than that of N 2 /H 2 –Ag@C@Co–N–C‐450 (148.0 m 2 /g). The higher surface area promoted sufficient exposure of active sites, 46,52 which facilitated a fast mass transfer process 53 . Besides, from the pore size distribution (Figure 4D, the inset), it is clear that the pore size of NH 3 –Ag@C@Co–N–C‐700 is in the range of 2–5 nm, while N 2 /H 2 –Ag@C@Co–N–C‐450 shows a wider pore size distribution in the range of 2–60 nm.…”

Porous spinel-type transition metal oxide nanostructures as emergent electrocatalysts for oxygen reduction reactions

“…CoFeCoO 4 spindle microparticle assembled rGO (CFCOSMs/rGO) and CoFeCoO 4 (CFCO-R) were synthesized via a hydrothermal (at 150 °C for 2 h) and sol–gel method (at 120 °C overnight), respectively. 142…”

“…CoFeCoO 4 spindle microparticle assembled rGO (CFCOSMs/rGO) and CoFeCoO 4 (CFCO-R) were synthesized via a hydrothermal (at 150 °C for 2 h) and sol-gel method (at 120 °C overnight), respectively. 142 CFCOSMs/rGO had a porous spindle microstructure that gave a superior ORR in terms of J L , b c and E onset (5.3 mA cm −2 ; 90.6 mV dec −1 ; 0.85 V vs. RHE), superior to CFCOSMs (5.2 mA cm −2 ; 101.1 mV dec −1 ; 0.76 V vs. RHE) and CFCO-R (4.5 mA cm −2 ; 101.9 mV dec −1 ; 0.763 V vs. RHE), although relatively close to Pt/C (5.6 mA cm −2 ; 15.6 mV dec −1 ; 0.95 V vs. RHE), and with the best stability. CFCOSMs/rGOs revealed the highest ORR activity among the CFCO-based materials due to the ideal overlap of the 3d orbital of Co 3+ and Fe 3+ with the O 2p orbital for effective charge transfer, coupled with the high conductivity and surface area of the rGO that improved the active sites for facile ORR.…”