In Situ Construction of MnO₂–Co₃O₄ Nanosheet Heterojunctions on Co@NCNT Surfaces for Oxygen Evolution

Abstract

Electrocatalytic water splitting is still circuitous and controversial because of the lack of highly active electrocatalysts to decrease the overpotential. Herein, we report a feasible method for constructing heterojunctions of MnO 2 −Co 3 O 4 nanosheets on Co@NCNT support surfaces (MnO 2 −Co 3 O 4 /Co@NCNT) by spontaneous redox reactions. Experimental results indicate that Co embedded in Co@NCNT can be used as the carbon support and anchoring sites for heterojunctions, thus exposing a large number of active sites, adjusting the surface electronic structure, changing the OER ratedetermining step of the catalyst, and reducing the reaction energy barrier. Besides, the in situ formation of MnO 2 −Co 3 O 4 nanosheets on Co@NCNT inhibits the loss and aggregation of the catalyst, leading to robust structural stability. Therefore, the synergistic effects of these factors provide multi-functional active sites to enhance the intrinsic activity and achieve maximum catalytic performances. To deliver a current density of 10 mA cm −2 , the catalyst of MnO 2 − Co 3 O 4 /Co@NCNT achieves an overpotential (η) of 303 mV in 1.0 M KOH media for OER. This simple redox strategy can be easily extended to prepare other ultrathin transition-metal oxide heterojunctions, which could be applied not only for water splitting but also for other energy conversion and storage technologies.

MnOx In Situ Growth-Induced Luminescence and Oxidase-Like Feature Bimodulation of CePO4:Tb Nanorods: Toward Ascorbic Acid-Related Bioanalysis in a “One-Stone-Two-Birds” Manner

“…In the high-resolution XPS of Mn 2p (Figure 1G), the two peaks at 653.2 and 641.3 eV can be assigned to the Mn 2p 1/2 and Mn 2p 3/2 spin states, respectively, and the spin-energy separation gap is 11.9 eV, indicating in situ formed manganese oxides with a Mn IV state. 35,36 Ce 3+ can be oxidized to Ce 4+ by KMnO 4 , but there is no distinct change in the Ce 3d XPS spectra of all samples (Figure S4), suggesting that only a fraction of Ce 3+ is oxidized to Ce 4+ with the KMnO 4 treatment. In addition, the change of the valence states was confirmed by the ζ potential, which exhibits a unique trend of increasing followed by decreasing with a change of the KMnO 4 concentration (Figure S6).…”

A Facile Preparation of Sandwich-Structured Pd/Polypyrrole-Graphene/Pd Catalysts for Formic Acid Electro-Oxidation

“…To further evaluate the intrinsic activity of FAO fuel cells, the electrochemically active surface area (ECSAs) is usually evaluated to explore the influence of the structural composition on the intrinsic activity of the catalyst, and the electrochemical double-layer capacitances (C dl ) obtained by CVs at different sweep speeds is positively correlated with the ECSAs. Therefore, C dl can be used to evaluate the number of electrochemically active sites exposed to different materials [ 36 , 37 ]. As can be seen from Figure 5 , Pd/PPy-Gns/Pd-modified GCE shows the largest double layer capacitance (26.3 mF cm −1 ), which proves that it has a large electrochemically active area, and has good formic acid oxidation activity, which is consistent with the test results of CV curve.…”

Application of changing the valence state of metals through the reaction time for efficient oxygen evolution reaction

“…38,39 Besides, carbon nanotubes (CNTs) can effectively accelerate electron transfer because they have the merits of a large specific surface area, low impedance, good chemical stability, and high conductivity. 40 The inclusion of CNTs in the preparation process is a common strategy to enhance a catalyst's conductivity and adjust the electronic structure of the catalyst. 41,42 Moreover, CNTs can act as bridges connecting various nanosheets, enabling a higher degree of connectivity among them.…”