Co₃O₄@Co/NCNT Nanostructure Derived from a Dicyanamide‐Based Metal‐Organic Framework as an Efficient Bi‐functional Electrocatalyst for Oxygen Reduction and Evolution Reactions

Abstract

There has been growing interest in the synthesis of efficient reversible oxygen electrodes for both the oxygen reduction reaction (ORR) and the oxygen evolution reactions (OER), for their potential use in a variety of renewable energy technologies, such as regenerative fuel cells and metal-air batteries. Here, a bi-functional electrocatalyst, derived from a novel dicyanamide based nitrogen rich MOF {[Co(bpe) (N(CN) )]⋅(N(CN) )⋅(5 H O)} [Co-MOF-1, bpe=1,2-bis(4-pyridyl)ethane, N(CN) =dicyanamide] under different pyrolysis conditions is reported. Pyrolysis of the Co-MOF-1 under Ar atmosphere (at 800 °C) yielded a Co nanoparticle-embedded N-doped carbon nanotube matrix (Co/NCNT-Ar) while pyrolysis under a reductive H /Ar atmosphere (at 800 °C) and further mild calcination yielded Co O @Co core-shell nanoparticle-encapsulated N-doped carbon nanotubes (Co O @Co/NCNT). Both catalysts show bi-functional activity towards ORR and OER, however, the core-shell Co O @Co/NCNT nanostructure exhibited superior electrocatalytic activity for both the ORR with a potential of 0.88 V at a current density of -1 mA cm and the OER with a potential of 1.61 V at 10 mA cm , which is competitive with the most active bi-functional catalysts reported previously.

FeNi Alloy Nanoparticles Encapsulated in Carbon Shells Supported on N‐Doped Graphene‐Like Carbon as Efficient and Stable Bifunctional Oxygen Electrocatalysts

“…As expected, the limiting current densities of the four samples increase with the increasing rotating speed owing to the accelerated mass transfer for soluble oxygen in the electrolyte. Moreover, the corresponding parallel and straight fitting Koutechy–Levich (K–L) lines of the four catalysts at different potentials are calculated as illustrated in Figures S4 b, S5 b, S5 d, and S5 f (in the Supporting Information), demonstrating that they have first‐order reaction kinetics in relation to the concentration of dissolved oxygen . The mean n values of ORR for FeNi@C/NG, Fe@C/NG, Ni@C/NG, and NG catalysts are 4.0, 3.9, 3.2, and 3.2, respectively.…”

Nickel Foam‐Supported Amorphous FeCo(Mn)−O Nanoclusters with Abundant Oxygen Vacancies through Selective Dealloying for Efficient Electrocatalytic Oxygen Evolution

“…The binding energies (BEs) of Fe 3+ are probed at 711.2 eV and 724.7 eV in the FeCo(Mn)−O/NF (Figure c) . Co 2p spectra of FeCo(Mn)−O/NF are deconvoluted into three groups of characteristic signals at 780.8 eV, 782.7 eV and 786.7 eV (satellite peak) for 2p3/2 as well as 796.8 eV, 798.1 eV and 803.0 eV (satellite peak) for 2p1/2 (Figure d), suggesting the coexistence of Co 3+ and Co 2+ . The O 1s region of FeCo(Mn)−O/NF exhibits four BEs at 529.9 eV, 530.9 eV, 531.5 eV and 532.0 eV (Figure e), which can be assigned respectively to lattice oxygen (O lat ), defective oxygen (O def ), metal hydroxide and absorbed water .…”

“…[34,35] Co 2p spectra of FeCo(Mn)À O/NF are deconvoluted into three groups of characteristic signals at 780.8 eV, 782.7 eV and 786.7 eV (satellite peak) for 2p3/2 as well as 796.8 eV, 798.1 eV and 803.0 eV (satellite peak) for 2p1/2 (Figure 3d), suggesting the coexistence of Co 3 + and Co 2 + . [36,37] The O 1s region of FeCo (Mn)À O/NF exhibits four BEs at 529.9 eV, 530.9 eV, 531.5 eV and 532.0 eV (Figure 3e), which can be assigned respectively to lattice oxygen (O lat ), defective oxygen (O def ), metal hydroxide and absorbed water. [10,17,[38][39][40] Notably, the peak area ratio for O def and O lat in the FeCo(Mn)À O/NF is almost four times higher than that in the FeCoMn/NF (4.89 vs. 1.21).…”

Hierarchically Porous Co−N−C Cathode Catalyst Layers for Anion Exchange Membrane Fuel Cells

“…After pyrolysis, the ZIF polyhedron morphology was distorted with abundant interconnected folds (Figure S3), resulted from the contraction process of ZIF precursor at high temperature . The high‐resolution (HR)TEM images (Figure S4) of ZIF‐CB‐ T show clear lattice figures with an interplanar distance of 0.207 nm, corresponding to Co (111) of the cubic metal . Several layers of graphene surrounding Co nanoparticles can be observed for that treated at 700 °C (Figure S4 b), forming a Co core and graphene shell structure, which can protect the Co nanoparticles from acid leaching .…”