Design of Hierarchical NiCo2O4 Nanocages with Excellent Electrocatalytic Dynamic for Enhanced Methanol Oxidation

Abstract

Although sheet-like materials have good electrochemical properties, they still suffer from agglomeration problems during the electrocatalytic process. Integrating two-dimensional building blocks into a hollow cage-like structure is considered as an effective way to prevent agglomeration. In this work, the hierarchical NiCo2O4 nanocages were successfully synthesized via coordinated etching and precipitation method combined with a post-annealing process. The nanocages are constructed through the interaction of two-dimensional NiCo2O4 nanosheets, forming a three-dimensional hollow hierarchical architecture. The three-dimensional supporting cavity effectively prevents the aggregation of NiCo2O4 nanosheets and the hollow porous feature provides amounts of channels for mass transport and electron transfer. As an electrocatalytic electrode for methanol, the NiCo2O4 nanocages-modified glassy carbon electrode exhibits a lower overpotential of 0.29 V than those of NiO nanocages (0.38 V) and Co3O4 nanocages (0.34 V) modified glassy carbon electrodes. The low overpotential is attributed to the prominent electrocatalytic dynamic issued from the three-dimensional hollow porous architecture and two-dimensional hierarchical feature of NiCo2O4 building blocks. Furthermore, the hollow porous structure provides sufficient interspace for accommodation of structural strain and volume change, leading to improved cycling stability. The NiCo2O4 nanocages-modified glassy carbon electrode still maintains 80% of its original value after 1000 consecutive cycles. The results demonstrate that the NiCo2O4 nanocages could have potential applications in the field of direct methanol fuel cells due to the synergy between two-dimensional hierarchical feature and three-dimensional hollow structure.

Investigation of the effect of thermal annealing of Ni-cobaltite nanoparticles on their structure, electronic properties and performance as catalysts for the total oxidation of dimethyl ether

“…The signals located at ∼780.96 and ∼797.24 eV are associated with Co 3+ whereas the peaks at ∼779.43 and ∼793.80 eV are assigned to Co 2+ species in NiCo 2 O 4 . 49,50 Additionally, the peaks located at ∼800 and 785 eV are assigned to satellite features. As far Co 3 O 4 is concerned, the Co 2p spectrum displays asymmetric peaks, with a slight shift from the lowest to highest BE, which are composed of several overlapping signals emerging from Co 2p 3/2 (∼780.38 eV) and Co 2p 1/2 (∼796.20 eV) peaks assigned to Co 2+ and Co 3+ .…”

“…, respectively, in accordance with the literature data. 13,50 Furthermore, the Fe 2p 3/2 of NiCo 2 O 4 is deconvoluted into the Ni 3+ and Ni 2+ components located at ∼856.30 and ∼854.62 eV, respectively, while that of Ni 2p 1/2 was also deconvoluted to two components at ∼871.44 and ∼873.13 eV, corresponding to the Ni 2+ and Ni 3+ , respectively. The signals ranging from ∼858 to ∼870 eV and those located behind ∼874 eV are assigned to satellite peaks.…”

Research progress of Co-based spinel oxide materials for direct methanol fuel cells

“…Zhan et al 83 prepared a NiCo 2 O 4 electrocatalyst in the form of fiber by a thermal decomposition method. In the study of electrocatalytic oxidation of methanol and ethanol, the fiber structure of NiCo 2 O 4 and the holes in the fiber (average 85 diameter of 20 nm) could accelerate the diffusion of reactant molecules on the catalyst, thus improving the electrocatalytic performance of the catalyst. Gu et al 84 used a rapid microwaveassisted synthesis plus calcination process to prepare 3D nanospheroidal NiCo 2 O 4 , which was composed of interwoven 2D ultra-thin mesoporous nanosheets.…”

“…This may be due to the unique porous nanospheroidal structure and large SSA. Li et al 85 successfully synthesized stratified NiCo 2 O 4 nanocages (NCs) through a collaborative etching and precipitation method (CEP) combined with post-annealing process, as shown in Fig. 10(e) and (f).…”

“…Schematic illustration of the proposed growth mechanism of NiCo 2 O 4 NCs (e). TEM images of the products monitored at different reaction times (f) 85.…”