Polyoxometalate‐Based Bottom‐Up Fabrication of Graphene Quantum Dot/Manganese Vanadate Composites as Lithium Ion Battery Anodes

Abstract

Lithium ion battery (LIB) electrodes require a stable connection between a redox-active metal oxide for charge storage and an electrically conductive (often carbon-based) material for charge transport. As charge transfer within the metal oxide is often a performance-limiting factor, one promising concept is the linking of charge transfer and charge storage components on the nanoscale. This would maximize the interfacial contact area and improve charging/discharging behavior. This work presents a one-step, room-temperature route giving nanostructured manganese vanadium oxide/graphene quantum dot (GQD) composite electrodes. Manganese vanadium oxide clusters are used as solution-processable precursors, which are deposited on GQDs using a sonication-driven conversion leading to electroactive, lightweight composites. Incorporation of the composites as anodes in LIBs shows high electrochemical performance featuring discharge capacities of 970 mAh g over 100 cycles with coulombic efficiencies near 100 %. The study shows how 3d-metal oxide/GQD nanostructures can be accessed by a scalable sonication route starting from soluble, chemically tunable metal oxide clusters and graphene quantum dots.

Differentiating Molecular and Solid‐State Vanadium Oxides as Active Materials in Battery Electrodes

“…As mentioned above, most of these studies focus on electrode preparation starting from hydrated POV salts where a thermal treatment step is involved to remove the water of hydration, which would otherwise lead to water electrolysis and H 2 /O 2 evolution, (“gassing”) at the typical voltages employed in LIBs and NIBs . However, thus far, little is known about the impact of the thermal dehydration treatment on the structural integrity of the POV clusters, although it literature‐known that POVs can easily convert into the corresponding solid‐state metal oxides by chemical, thermal, or even ultrasonic energy input …”

“…[16] However, thus far, little is known about the impact of the thermal dehydration treatment on the structural integrity of the POV clusters, although it literature-known that POVs can easily convert into the corresponding solid-state metal oxides by chemical, [17][18][19] thermal [18,20] or even ultrasonic energy input. [21]…”

Aerobic Oxidation Catalysis by a Molecular Barium Vanadium Oxide

“…To enable a targeted metal‐functionalization of vanadate clusters, we developed a chloride‐templated vanadate “host” cluster (Me 2 NH 2 ) 2 [V 12 O 32 Cl] 3− (= {V 12 } ) featuring two Me 2 NH 2 + ‐blocked metal binding sites . Incorporation of one or two reactive 3d metal “guests” is possible, leading to metal‐functionalized vanadates as multi‐electron transfer sites, for example, in battery electrodes or as catalysts for C−H‐activation and alcohol oxidation . Based on these studies, we became interested in expanding this “host–guest” assembly strategy by developing a vanadate “host” capable of binding larger metals, for example, large alkali or alkali earth cations.…”

Transition‐Metal Oxides/Carbides@Carbon Nanotube Composites as Multifunctional Electrocatalysts for Challenging Oxidations and Reductions

“…Multiwalled carbon nanotubes (MWCNTs) werep retreated with concentrated HNO 3 (65 %) to introduce oxidized surfacec arbon groups (e.g., ÀCOH, ÀCOOH) suitable for metal oxide anchoring. [33,40] Stable anchoring of the metal oxidesa nd carbides on the MWCNTsw as then achievedb yc alcination of the composite at 600, 750, and 900 8C. [39] For the deposition of the precursor on multiwalled CNTs, we used ar ecently established mild sonication route.…”

“…[24][25][26] In this work, we used manganese vanadium oxide cluster anionsa sm olecular precursors for metal oxides and carbides. [33] Therefore, the deposition of Mn-V-oxides and -carbides based on the corresponding Mn-V-basedP OMso nn anostructured carbonc ould be an ideal approach for highlya ctive electrocatalyst design. Although molecular polyoxometalates (POMs) are well known for their multielectront ransfer reactivity (e.g.,f or the OER, ORR, and hydrogen-evolution reactions), [27][28][29][30] their stable linkaget oc onductive substrates is still ac hallenge owing to their solubility in many commone lectrolytes, particularly in water.…”