Hierarchically Assembled Cobalt Oxynitride Nanorods and N-Doped Carbon Nanofibers for Efficient Bifunctional Oxygen Electrocatalysis with Exceptional Regenerative Efficiency

Abstract

Oxygen-based electrocatalysis is an integral aspect of a clean and sustainable energy conversion/storage system. The development of economic bifunctional electrocatalysts with high activity and durability during reversible reactions remains a great challenge. The tailored porous structure and separately presented active sites for oxygen reduction and oxygen evolution reactions (ORR and OER) without mutual interference are most crucial for achieving desired bifunctional catalysts. Here, we report a hybrid composed of sheath–core cobalt oxynitride (CoO x @CoN y ) nanorods grown perpendicularly on N-doped carbon nanofiber (NCNF). The brush-like CoO x @CoN y nanorods, composed of metallic Co4N cores and oxidized surfaces, exhibit excellent OER activity (E = 1.69 V at 10 mA cm–2) in an alkaline medium. Although pristine NCNF or CoO x @CoN y alone had poor catalytic activity in the ORR, the hybrid showed dramatically enhanced ORR performance (E = 0.78 V at −3 mA cm–2). The experimental results coupled with a density functional theory (DFT) simulation confirmed that the broad surface area of the CoO x @CoN y nanorods with an oxidized skin layer boosts the catalytic OER, while the facile adsorption of ORR intermediates and a rapid interfacial charge transfer occur at the interface between the CoO x @CoN y nanorods and the electrically conductive NCNF. Furthermore, it was found that the independent catalytic active sites in the CoO x @CoN y /NCNF catalyst are continuously regenerated and sustained without mutual interference during the round-trip ORR/OER, affording stable operation of Zn–air batteries.

Single-Atom and Bimetallic Nanoalloy Supported on Nanotubes as a Bifunctional Electrocatalyst for Ultrahigh-Current-Density Overall Water Splitting

“…19,20 (2) Due to the nanoscale confinement effect, the NiFe (oxy)hydroxides and NiCo (oxy)hydroxides generated on the surface of NiFe and NiCo nanoalloys are extremely thin (1− 5 nm), which neither hinder the migration of electrons in the OER process nor affect the adsorption/desorption of the intermediate products on NiFe and NiCo alloys in the catalytic process. 21,22 In addition, NiFe and NiCo alloys have high conductivity, which are beneficial for efficient electron transfer in catalytic processes. (3) A CNT as the support of these composite catalysts, which is a good electric conductor, can avoid the agglomeration of nanoparticles.…”

Surface Reconstruction of Co4N Coupled with CeO2 toward Enhanced Alkaline Oxygen Evolution Reaction

“…CeO 2 /Co 4 N still possesses an overpotential of 336 mV at 10 mA cm –2 after 2000 cycles (Figure e). As shown in Figure f, the OER activity of CeO 2 /Co 4 N displays no significant decrease after 10 h. Besides, the OER activity (Figure g) of CeO 2 /Co 4 N is comparable to or even superior to those of most reported non-noble metal electrocatalysts, suggesting the potential of alkaline OER application. − …”

“…(f) I–t curves of CeO 2 /Co 4 N at 318 mV. (g) Comparison with the overpotentials of the reported OER electrocatalysts at 10 mA cm –2 . − …”

Recent Developments in Carbon-Based Nanocomposites for Fuel Cell Applications: A Review

“…These characteristics indicated that CNTs/CNFs are promising catalysts for MFCs applications. Yoon et al [77] demonstrated the CoOx@CoNy/NCNF550-catalyst-coated MEA used for ORR application. Figure 7a illustrates the fabrication processes of CoOx@CoNy/NCNFs achieved at various nitridation temperatures.…”