Self‐Catalyzed Growth of Co–N–C Nanobrushes for Efficient Rechargeable Zn–Air Batteries

Abstract

have been considered as attractive alternatives in next-generation energy storage systems due to their high energy density, safety, and environmental friendliness. [2] The big challenge for this technique is the development of highly efficient and stable air electrode. It requires highly active electrocatalysts for both oxygen reduction reactions (ORR) and oxygen evolution reactions (OER) to overcome sluggish kinetics for four electron transfer processes and significantly reduce the reaction overpotentials. [3] Although noblemetal-based catalysts, such as platinum (Pt), ruthenium (Ru), iridium (Ir), and their alloys, are the best-known oxygen electrocatalysts, their commercialization are greatly hindered by their reserves, high cost, and still insufficient catalytic performance for bifunctional oxygen reactions. [4] Over the past few years, much efforts have been devoted to developing non-noble metal bifunctional electrocatalysts, such as transition metal sulfide/oxides, [5] nitrides, [6] carbon materials, [7] and so on. [8] Among these catalysts, the transitional metal-containing N-doped carbon materials (M-N-C, M = Fe, Co, Ni, etc.) have attracted intense attention. The transition metals in such catalysts greatly enhance the graphitization and thus electrical conductivity of carbon matrix, which provide them the better protection in turn from corrosion and aggregation during the electrochemical reactions. [4b,9] Furthermore, the interactions and synergistic effects between metal species and N-doped carbon species enhance the intrinsic electrochemical activity for ORR and OER by electronically modulating the charge distribution on active sites and thus the adsorption/ desorption of O 2 and intermediates. [4c,10] M-N-C materials are usually obtained from the direct pyrolysis of precursors, such as transition metal macrocycles/ polymers (e.g., porphyrins and phthalocyanines) or the mixture of nitrogen-rich organic compounds and transition-metal salts, which commonly gives the inhomogeneous microstructures and uncontrollable agglomeration of active components due to the high reactivity of transition metal at high-temperature. Such structure could lead to the insufficient exposure of active sites as well as poor electron and mass transport. [11] 1D nanostructures such as nanotubes, [12] nanofibers, [13] nanorod, [14] etc., were thus introduced to improve the electron transportation. The shortcoming is the insufficient surface area for accommodating Highly efficient and stable bifunctional electrocatalysts for oxygen reduction and evolution are essential for aqueous rechargeable Zn-air batteries, which require highly active sites as well as delicate structural design for increasing effective active sites and facilitating mass/electron transfer. Herein, a scalable and facile self-catalyzed growth strategy is developed to integrate highly active Co-N-C sites with 3D brush-like nanostructure, achieving Co-N-C nanobrushes with Co,N-codoped carbon nanotube branches grown on Co,Ncodoped nanoparticle assembled na...

A Self‐Jet Vapor‐Phase Growth of 3D FeNi@NCNT Clusters as Efficient Oxygen Electrocatalysts for Zinc‐Air Batteries

“…Although almost all of the metal nuclei are embedded in the tips of the CNTs, some of them are still embedded within the CNTs. [36,37] Distinct from the morphology of FeNi@NCNT-CP, the carbonized CP retains its pristine textile morphology, with a slightly rough surface, while FeNi@NCNT without CP comprises a random mix of CNT and larger carbon particles instead of uniform CNT arrays, respectively ( Figure S1, Supporting Information). If the urea, metal salt, and CP were mixed directly and then heated in a corundum boat, the CNT clusters cannot be obtained.…”

Magnetic Field Assisted Construction of Hollow Red P Nanospheres Confined in Hierarchical N‐Doped Carbon Nanosheets/Nanotubes 3D Framework for Efficient Potassium Storage

“…Analogously, the more electron‐deficient P x ′, P x ″, P y ′ , and P x ″ are obtained with further disassociation from P 4 to P 2 under continuous annealing, and eventually to the red P. All these electro‐deficient intermediates will be captured immediately by the electron‐enriched Fe NPs when exposed to magnetic field, due to the strong electrostatic self‐assembly force existing between the conversion intermediates and polarized Fe host as well as the spontaneous chemical bonding of active Fe 3d zx and P 3s x . [ 31 ] In the absence of magnetic field, all PP bonds still break at 260 °C; however, the deposition of P species is random over Fe, and finally, most of the obtained P NPs are basically solid (Figure S16, Supporting Information).…”

Recent advances in the field of carbon-based cathode electrocatalysts for Zn–air batteries

“…71 The amorphous characteristics of the Fe 0. intermediates. 72 Hu group reported a 3D hierarchical Co-N-C brush-like nanostructure by N-doped carbon encased Co NPs by self-catalyzed growth (denoted as CoNC-NB) (Fig. 7e).…”