We carried out in operando Mo K-edge X-ray absorption fine structure measurements on the rechargeable molecular cluster batteries (MCBs) of polyoxometalates (POMs), in which a Keggin-type POM, [PMo(12)O(40)](3-), is utilized as a cathode active material with a lithium metal anode. The POM-MCBs exhibit a large capacity of ca. 270 (A h)/kg in a voltage range between V = 4.0 V and V = 1.5 V. X-ray absorption near-edge structure analyses demonstrate that all 12 Mo(6+) ions in [PMo(12)O(40)](3-) are reduced to Mo(4+) in the discharging process. This means the formation of a super-reduced state of the POM, namely, [PMo(12)O(40)](27-), which stores 24 electrons, and this electron number can explain the large capacity of the POM-MCBs. Furthermore, extended X-ray absorption fine structure analyses reveal the molecular structure of [PMo(12)O(40)](27-), which is slightly reduced in size compared to the original [PMo(12)O(40)](3-) and involves Mo(4+) metal-metal-bonded triangles. Density functional theory calculations suggest that these triangles are formed because of the large number of additional electrons in the super-reduced state.

Geladene Cluster: Ein Hybridsystem aus einwandigen Kohlenstoffnanoröhren (SWNTs) mit individuell oberflächenadsorbierten Polyoxometallat(POM)‐Molekülen kann als kathodenaktives Material in wiederaufladbaren Lithiumbatterien eingesetzt werden. Eine so aufgebaute POM/SWNT‐Batterie war durch eine sehr hohe Kapazität (>300 Ah kg−1) und kurze Lade/Entladezeiten (<2 h) charakterisiert.

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Nickel-based hydroxide hierarchical nanoarrays (NiyM(OH)x HNAs M = Fe or Zn) are doped with non-noble transition metals to create nanostructures and regulate their activities for the oxygen evolution reaction. Catalytic performance in these materials depends on their chemical composition and the presence of nanostructures. These novel hierarchical nanostructures contain small secondary nanosheets that are grown on the primary nanowire arrays, providing a higher surface area and more efficient mass transport for electrochemical reactions. The activities of the NiyM(OH)x HNAs for the oxygen evolution reaction (OER) followed the order of Ni2.2Fe(OH)x > Ni(OH)2 > Ni2.1Zn(OH)x, and these trends are supported by density functional theory (DFT) calculations. The Fe-doped nickel hydroxide hierarchical nanoarrays (Ni2.2Fe(OH)x HNAs), which had an appropriate elemental composition and hierarchical nanostructures, achieve the lowest onset overpotential of 234 mV and the smallest Tafel slope of 64.3 mV dec−1. The specific activity, which is normalized to the Brunauer–Emmett–Teller (BET) surface area of the catalyst, of the Ni2.2Fe(OH)x HNAs is 1.15 mA cm−2BET at an overpotential of 350 mV. This is ~4-times higher than that of Ni(OH)2. These values are also superior to those of a commercial IrOx electrocatalyst.

Highly efficient low-cost electrocatalysts for water splitting have attracted increasing interest in the development of energy storage and conversion. Here, we utilized copper (Cu) weaving mesh to in situ fabricate earthabundant elements-based integrated electrodes for high performance water splitting, where NiFe layered double hydroxide (NiFe-LDH) ultrathin nanoarrys for oxygen evolution reaction (OER) and Cu 3 P nanowires for hydrogen evolution reaction (HER) were successfully constructed on the Cu mesh. Notably, large stable current densities are obtained for both OER (600 mA cm −2 ) and HER (200 mA cm −2 ) electrodes under low overpotential, which is superior to most of the nanoparticle-based electrodes. The large current density is mainly because of the excellent conductivity and clean surface (binderfree) of the Cu mesh-based electrode, and which is extremely important for industrial application. The prepared integrated electrodes are coupled with a macroscopic porous sieve and microscopic nanostructures. The assembled NiFe-LDH∥Cu 3 P electrolyzer exhibits a small cell working voltage of 1.72 V under the current density of 10 mA cm −2 at room temperature, as well as long-term stabilities (>10 h) in 1 M KOH. These excellent performances of our earth-abundant elements-based weaving mesh electrode result from their improved charge transfer, surface area, mass transport, and faster kinetics of catalytic reactions.

We report a cooperative enhancement of the capacitor effects of RGO induced by nanohybridization with POM.

In situ X-ray absorption fine structure (XAFS) analyses were performed on rechargeable molecular cluster batteries (MCBs), which were formed by a lithium anode and cathode-active material, [Mn(12)O(12)(CH(3)CH(2)C(CH(3))(2)COO)(16)(H(2)O)(4)] with tert-pentyl carboxylate ligand (abbreviated as Mn12tPe), and with eight Mn(3+) and four Mn(4+) centers. This mixed valence cluster compound is used in an effort to develop a reusable in situ battery cell that is suitable for such long-term performance tests. The Mn12tPe MCBs exhibit a large capacity of approximately 210 Ah kg(-1) in the voltage range V=4.0-2.0 V. The X-ray absorption near-edge structure (XANES) spectra exhibit a systematic change during the charging/discharging with an isosbestic point at 6555 eV, which strongly suggests that only either the Mn(3+) or Mn(4+) ions in the Mn12 skeleton are involved in this battery reaction. The averaged manganese valence, determined from the absorption-edge energy, decreased monotonically from 3.3 to 2.5 in the first half of the discharging (4.0>V>2.8 V), but changed little in the second half (2.8>V>2.0 V). The former valence change indicates a reduction of the initial [Mn12](0) state by approximately ten electrons, which corresponds well with the half value of the observed capacity. Therefore, the large capacity of the Mn12 MCBs can be understood as being due to a combination of the redox change of the manganese ions and presumably a capacitance effect. The extended X-ray absorption fine structure (EXAFS) indicates a gradual increase of the Mn(2+) sites in the first half of the discharging, which is consistent with the XANES spectra. It can be concluded that the Mn12tPe MCBs would include a solid-state electrochemical reaction, mainly between the neutral state [Mn12](0) and the super-reduced state [Mn12](8-) that is obtained by a local reduction of the eight Mn(3+) ions in Mn12 toward Mn(2+) ions.

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