Interaction Induced High Catalytic Activities of CoO Nanoparticles Grown on Nitrogen-Doped Hollow Graphene Microspheres for Oxygen Reduction and Evolution Reactions

Abstract

Nitrogen doped graphene hollow microspheres (NGHSs) have been used as the supports for the growth of the CoO nanoparticles. The nitrogen doped structure favors the nucleation and growth of the CoO nanoparticles and the CoO nanoparticles are mostly anchored on the quaternary nitrogen doped sites of the NGHSs with good monodispersity since the higher electron density of the quaternary nitrogen favors the nucleation and growth of the CoO nanoparticles through its coordination and electrostatic interactions with the Co 2+ ions. The resulting NGHSs supported CoO nanoparticles (CoO/NGHSs) are highly active for the oxygen reduction reaction (ORR) with activity and stability higher than the Pt/C and for the oxygen evolution reaction (OER) with activity and stability comparable to the most efficient catalysts reported to date. This indicates that the CoO/NGHSs could be used as efficient bi-functional catalysts for ORR and OER. Systematic analysis shows that the superior catalytic activities of the CoO/ NGHSs for ORR and OER mainly originate from the nitrogen doped structure of the NGHSs, the small size of the CoO nanoparticles, the higher specific and electroactive surface area of the CoO/NGHSs, the good electric conductivity of the CoO/NGHSs, the strong interaction between the CoO nanoparticles and the NGHSs, etc.Unitized regenerative fuel cells (UNFCs) and metal-air batteries have been identified as the promising energy conversion and storage devices with great potential to alleviate the ever-increasing pressure from the energy deficiency 1-4 . However, their widespread applications in the real-world devices have been greatly hindered by the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), both of which are the key electrode processes of UNFCs and metal-air batteries [3][4][5][6] . The development of oxygen electrode catalysts that are active for both the ORR and the OER presents a great challenge, since the catalysts efficient for the ORR usually tend to be poor for the OER and vice versa 7,8 . For instance, precious metals such as platinum (Pt) and its alloys which are well-known ORR catalysts are poor for the OER, while iridium and ruthenium oxide-based catalysts which have extraordinary OER activity exhibit low ORR activity 9-12 . Although integration of precious metals with iridium/ruthenium oxide might be a promising way to fabricate bifunctional catalysts with high efficiency for the ORR and the OER 13-15 , their practical uses in UNFCs and metal-air batteries have been greatly limited by high cost, scarcity, and poor stability. Extensive efforts have therefore been devoted to the development of alternative low-cost and high-performance oxygen electrode catalysts with improved efficiency and stability 8,16,17 .Recent work has demonstrated the potential use of transition-metal oxides (TMOs) as bifunctional catalysts for the ORR and the OER 1,8,[18][19][20] . However, the TMOs prepared by the traditional synthetic routes usually possess large particle sizes and low specific...

Co3O4-graphene nanoflowers as anode for advanced lithium ion batteries with enhanced rate capability

“…These results consistent with the XPS spectra of the hydrothermal reduction products of GO reported previously, suggesting the presence of rGO. [33,34] All the aforementioned results confirm the successful synthesis of the CGF composite.…”

A rational method to kinetically control the rate-determining step to explore efficient electrocatalysts for the oxygen evolution reaction

“…Controlling the RDS via hybridization with a small amount of electronwithdrawing RuO 2 NSs provides a novel, rational method to explore economically feasible efficient electrocatalysts. In comparison with previously reported, efficient, RuO 2 -based OER electrocatalysts showing low overpotentials of 360 mV for commercial 20 wt% RuO 2 /C (Ru:~14 wt%) 39 , 290 mV for RuO 2 -loaded on Ti plates (Ru:~74 wt%) 40 , and 220 mV for (100)-oriented rutile RuO 2 (Ru:~74 wt%) 41 , the present NFR10 nanohybrid with a much smaller Ru content of~0.7 wt% displays a much lower overpotential of 207 mV at 10 mA cm −2 , highlighting the usefulness of the present synthetic strategy in exploring novel, efficient electrocatalysts. The very low Ru content of the present nanohybrid provides this material with a high level of economic feasibility over that of conventional RuO 2 -based OER electrocatalysts.…”

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Surfactant Intercalated Mono‐metallic Cobalt Hydrotalcite: Preparation, Characterization, and its Bi‐functional Electrocatalytic Application

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