Two-Dimensionally Confined Water in between MnO<sub>2</sub>Layers of Na-Birnessite

Matsui, Hiroshi; Ju, Jing; Odaira, Tomohiro; Toyota, Naoki

doi:10.1143/jpsj.78.074801

Cited by 14 publications

(9 citation statements)

References 24 publications

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“…The role of water molecules is mainly as a structure stabilizer (15), removal of which causes little change to the electronic structure according to a recent computation (16). Hence, we choose the pure hexagonal MnO2 to study the intrinsic properties, without cation or water intercalation and with the experimental interlayer spacing.…”

Section: Resultsmentioning

confidence: 99%

Redox properties of birnessite from a defect perspective

Peng

McKendry

Ding

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Birnessite, a layered-structure MnO 2 , is an earth-abundant functional material with potential for various energy and environmental applications, such as water oxidation. An important feature of birnessite is the existence of Mn(III) within the MnO 2 layers, accompanied by interlayer charge-neutralizing cations. Using first-principles calculations, we reveal the nature of Mn(III) in birnessite with the concept of the small polaron, a special kind of point defect. Further taking into account the effect of the spatial distribution of Mn(III), we propose a theoretical model to explain the structure-performance dependence of birnessite as an oxygen evolution catalyst. We find an internal potential step which leads to the easy switching of the oxidation state between Mn(III) and Mn(IV) that is critical for enhancing the catalytic activity of birnessite. Finally, we conduct a series of comparative experiments which support our model.birnessite MnO 2 | small polaron | catalysis | water oxidation P hotoelectrochemical (PEC) splitting of water into H2 and O2 (artificial photosynthesis) provides an attractive way to harvest solar energy. The process consists of the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), both of which are facilitated with catalysts in practice. Currently, one of the biggest challenges is to develop a cheap and efficient catalyst for the former reaction with a low overpotential, which is still needed to overcome the kinetic barriers (already lowered by the catalyst) along the path from reactants to products. Birnessite, similar to the oxygen-evolving complex in Photosystem II for photosynthesis in regard to the coexistence of Mn(III) (nominal Mn 3+ ) and Mn(IV) (nominal Mn 4+ ) within its structure (1-3), has already shown a moderate catalytic performance with the overpotentials reported from 0.6 V to 0.8 V (4-8).Birnessite has the general formula Mx MnO2·1.5(H2O), composed of layers of edge-sharing MnO6 octahedra as shown in Fig. 1 for the hexagonal phase, and an interlayer of randomly distributed water molecules and metal (M) cations (like K + , Na + , and Ca 2+ ). With the charge balanced by the interlayer cations, some of the Mn cations within the MnO2 layer are reduced from Mn(IV) to Mn(III). The coexistence of Mn(IV) and Mn(III), and further the "balanced equilibrium" or low energy barrier between them, has been suspected to be a critical factor for its catalytic activity (1). The importance of the high-spin Mn(III), through its e 1 g electronic configuration, has been realized in other manganese oxides for OER catalysis (2, 9) and also follows the design principle of Suntivich et al. (10) that a near-unity eg occupancy may imply good OER catalytic activity. This easy switching of the oxidation state is also a typical behavior for the transition metal cation undergoing back and forth changes between several oxidation states in OER catalysts during the water oxidation cycle (11-13). OER catalysts like Co-and Ni-doped hematite (12) and cobalt oxides (13), as well as ...

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Section: Resultsmentioning

confidence: 99%

Redox properties of birnessite from a defect perspective

Peng

McKendry

Ding

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…The XRD patterns of the prepared Na 0.35 MnO 2 /CNT nanocomposite and Na 0.35 MnO 2 nanowires are shown in Figure 1a. The peaks at about 17.1° and 25° are assigned to the diffraction of (001) and (002) planes, respectively, indicating the layered structure of Na 0.35 MnO 2 28. Because of the characteristic diffraction peak of carbon nanotubes at 26° 29 located nearby, the peak intensity of the Na 0.35 MnO 2 /CNT nanocomposite at 25° is much higher than that of Na 0.35 MnO 2 .…”

Section: Resultsmentioning

confidence: 97%

Na_0.35MnO₂/CNT Nanocomposite from a Hydrothermal Method as Electrode Material for Aqueous Supercapacitors

Zhang

et al. 2014

Zeitschrift anorg allge chemie

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A Na 0.35 MnO 2 /CNT nanocomposite is prepared by a simple and low energy consumption hydrothermal method. Its electrochemical performance as an electrode material for asymmetric supercapacitors with aqueous Na 2 SO 4 solution is investigated. In this nanocomposite less than 2 wt-% of CNTs are intermingled with the Na 0.35 MnO 2 nanowires. Quite obviously the introduced CNTs efficiently improve the rate performance of the composite. When the current density increases from 0.1 to 10 A·g -1 , the capacitance decreases only slightly from 163 to 125 F·g -1 . When assembled into an asymmetric aqueous supercapacitor using activated carbon as the counter electrode and an

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“…In general, one expects the concentration of Mn(III) to vary with the equivalents of counterion charge in the interlayer. Matsui et al (71) reported the average oxidation state of manganese in similar materials by measuring the ratio of Na + to manganese in the solid using ICP analysis, since the concentration of Na + should be equal to that of Mn(III) in the layer. In their samples, the ratio of Mn(III) to Mn(IV) was 0.28:0.72 (71) calculating the average oxidation state of manganese to be 3.72.…”

Section: Manganese-oxide Filmmentioning

confidence: 99%

Manganese-Oxide Solids as Water-Oxidation Electrocatalysts: The Effect of Intercalating Cations

Tao

Stich

Jaccard

et al. 2015

ACS Symposium Series

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A set of birnessite-type manganese oxides with both monovalent alkaline cations (Li + , Na + , K + , Rb + or Cs +) and divalent alkaline-earth cations (Ca 2+ or Mg 2+) has been synthesized using electrolytic deposition methods. X-ray diffraction gives typical birnessite-type patterns, with diffraction peaks at 2θ = 12.01°and 24.7°assigned to (001) and (002) planes. Electron paramagnetic resonance spectra suggest differences in the stability of Mn(III) species in manganese-oxide layer, which is more stable in birnessite samples with divalent cations than samples with monovalent cations. The activity of samples for an anodic O 2-evolution reaction is considerably affected by electrostatic potential and Lewis acidity of the monovalent cation, following the sequence of Li + > Na + > K + > Rb + > Cs +. While for samples with intercalating divalent alkaline-earth cations, there was slightly lower activity for O 2 evolution, which may be correlated to different stability of Mn(III) species in the birnessite layers. In addition, we observed much higher O 2-evolution activity at an overpotential of ca. 220-230 mV if the samples were heat-treated between 300-500°C once they were electrolytically deposited as LiMnO x films. Clearly dry heating causes changes in both the crystalline structure and electronic structure of manganese-oxide layers, as indicated by associated changes in water-oxidation activity.

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Two-Dimensionally Confined Water in between MnO₂Layers of Na-Birnessite

Cited by 14 publications

References 24 publications

Redox properties of birnessite from a defect perspective

Redox properties of birnessite from a defect perspective

Na_0.35MnO₂/CNT Nanocomposite from a Hydrothermal Method as Electrode Material for Aqueous Supercapacitors

Manganese-Oxide Solids as Water-Oxidation Electrocatalysts: The Effect of Intercalating Cations

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Two-Dimensionally Confined Water in between MnO2Layers of Na-Birnessite

Cited by 14 publications

References 24 publications

Redox properties of birnessite from a defect perspective

Redox properties of birnessite from a defect perspective

Na0.35MnO2/CNT Nanocomposite from a Hydrothermal Method as Electrode Material for Aqueous Supercapacitors

Manganese-Oxide Solids as Water-Oxidation Electrocatalysts: The Effect of Intercalating Cations

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Two-Dimensionally Confined Water in between MnO₂Layers of Na-Birnessite

Na_0.35MnO₂/CNT Nanocomposite from a Hydrothermal Method as Electrode Material for Aqueous Supercapacitors