Polyoxomolybdate–Polypyrrole/Reduced Graphene Oxide Nanocomposite as High-Capacity Electrodes for Lithium Storage

A nanocomposite polyoxomolybdate (PMo₁₂)–polypyrrole (PPy)/reduced graphene oxide (RGO) is fabricated by using a simple one-pot hydrothermal method as an electrode material for lithium-ion batteries. This facile strategy skillfully ensures that individual polyoxometalate (POM) molecules are uniformly immobilized on the RGO surfaces because of the wrapping of polypyrrole (PPy), which avoids the desorption and dissolution of POMs during cycling. The unique architecture endows the PMo₁₂–PPy/RGO with the lithium storage behavior of a hybrid battery–supercapacitor electrode: the nanocomposite with a lithium storage capacity delivers up to 1000 mAh g^–1 at 100 mA g^–1 after 50 cycles. Moreover, it still demonstrates an outstanding rate capability and a long cycle life (372.4 mAh g^–1 at 2 A g^–1 after 400 cycles). The reversible capacity of this nanocomposite has surpassed most pristine POMs and POMs-based electrode materials reported to date

CoV₂O₆–V₂O₅ Coupled with Porous N‑Doped Reduced Graphene Oxide Composite as a Highly Efficient Electrocatalyst for Oxygen Evolution

Electrocatalysts with high intrinsic activity for the oxygen evolution reaction (OER) are greatly desired for sustainable oxygen-based electrochemical energy conversion. In this work, the bimetallic oxide composite consisting of CoV₂O₆ and V₂O₅ anchoring on nitrogen-doped reduced graphene oxide (CoV₂O₆–V₂O₅/NRGO-1) was synthesized directly by carbonization of the polyoxometalates, ethylenediamine, and graphene oxide precursors. CoV₂O₆–V₂O₅/NRGO-1 used as an electrocatalyst exhibits an ultralow overpotential of 239 mV vs RHE at the current density of 10 mA cm^–2 and excellent stability in 1 M KOH. Surprisingly, it has high intrinsic activity with the turnover frequency of 1.80 s^–1 at the overpotential of 300 mV, which is the highest among the electrocatalysts reported to date. Theoretical calculation proves that the outstanding electrocatalytic performance is attributed to synergistic effects, in which CoV₂O₆ acts as active sites while the hydrogen bond between V₂O₅ and intermediate HOO* of the OER greatly decreases the composite adsorption energy, thus reducing the overpotential. Most importantly, the results demonstrate for the first time that intermolecular hydrogen bonding plays a key role in improving electrocatalytic properties for the OER, which reveals a new method of designing novel OER electrocatalysts