Defect‐Engineered Ultrathin δ‐MnO₂ Nanosheet Arrays as Bifunctional Electrodes for Efficient Overall Water Splitting

Abstract

Recently, defect engineering has been used to intruduce half‐metallicity into selected semiconductors, thereby significantly enhancing their electrical conductivity and catalytic/electrocatalytic performance. Taking inspiration from this, we developed a novel bifunctional electrode consisting of two monolayer thick manganese dioxide (δ‐MnO2) nanosheet arrays on a nickel foam, using a novel in‐situ method. The bifunctional electrode exposes numerous active sites for electrocatalytic rections and displays excellent electrical conductivity, resulting in strong performance for both HER and OER. Based on detailed structure analysis and density functional theory (DFT) calculations, the remarkably OER and HER activity of the bifunctional electrode can be attributed to the ultrathin δ‐MnO2 nanosheets containing abundant oxygen vacancies lead to the formation od Mn3+ active sites, which give rise to half‐metallicity properties and strong H2O adsorption. This synthetic strategy introduced here represents a new method for the development of non‐precious metal Mn‐based electrocatalysts for eddicient energy conversion.

Mass‐Production of Mesoporous MnCo2O4 Spinels with Manganese(IV)‐ and Cobalt(II)‐Rich Surfaces for Superior Bifunctional Oxygen Electrocatalysis

“…[4] Among the developed bifunctional oxygen-catalysts, [5] heteroatom-doped carbon materials have been paid much attention because heteroatom doping can change the asymmetry spin density and the local charge density of carbon lattice. [6] Thevariation of structure or components often involve some complicated processes and the yield is limited. [5c,d] In contrast, metal oxides are easily synthesized at lower temperatures.H owever,o rdinary pure metal oxides with ideal crystal structure often only exhibit electrocatalysis activity of either OER or ORR.…”

Enhancement of Oxygen Transfer by Design Nickel Foam Electrode for Zinc−Air Battery

“…The peaks of Mn 2p 1/2 and Mn 2p 3/2 were centered at 654.0 and 642.5 eV, respectively, with a spin energy of 11.5 eV; these values are consistent with previously reported data. 61,64 Deconvoluted Mn 2p 3/2 peaks at 642.6 and 641.8 eV are attributed to the presence of Mn 4+ and Mn 3+ oxide phases, respectively. [65][66][67] The amount of Mn 4+ and Mn 3+ oxide phases is determined to be 94% and 6%, respectively, which indicates that the dominated oxidation state of manganese oxide in the composites is tetravalent oxide.…”

“…In addition, the presence of Mn 3+ leads to better electrocatalytic performance due to oxygen defects in the material. [59][60][61] Fig. 3i presents the fitted O 1 s spectrum, which contains one sharp peak at 530 eV and two broad peaks at 531.6 and 532.6 eV.…”

“…This result agrees well with the reported structure for δ-MnO 2 on Ni foam. 61,63 XPS was used to probe the chemical states of Mn and O on the electrode surface. Fig.…”

Manganese Oxide Modified Nickel Catalysts for Photothermal CO Hydrogenation to Light Olefins

“…On increasing the reduction temperature from 450 to 600 °C (temperatures at which all Ni is present as Ni 0 ), the intensity of the metallic Ni feature actually became more intense than that of the reference Ni-foil. Such changes might originate from defects in the MnO, [23] which in turn might have resulted in subtle variations in the valence state of the supported metallic Ni nanoparticles (ranging between 0 and some δ − value). In the Mn K-edge EXAFS spectra, coordination numbers about metal atoms correlate with shell intensities.…”