Heteroatom enhanced sodium ion capacity and rate capability in a hydrogel derived carbon give record performance in a hybrid ion capacitor.

We employed a polypyrrole hydrogel precursor to create a carbon framework that possesses both huge heteroatom content (13 wt% nitrogen and 11 wt% oxygen) and high surface area (945 m 2 g −1 ) that is equally divided between micropores and mesopores. A sodium ion capacitor (NIC, HIC) electrode fabricated from this N and O Functionalized Carbon (NOFC) has tremendous reversible capacity and rate capability, e.g. 437 mA h g −1 at 100 mA g −1 , and 185 mA h g −1 at 1600 mA g −1 . This is among the most favorable reported, and is due to copious nanoporosity that enables fast ion sorption at the many N and O moieties and graphene defects. The NOFC imbues a NIC device with energy–power characteristics that are not only state-of-the-art for Na hybrids, but also rival Li systems: Ragone chart placement is 111 W h kg −1 and 38 W h kg −1 at 67 W kg −1 and 14,550 W kg −1 , respectively, with 90% capacity retention at over 5000 charge/discharge cycles. [ABSTRACT FROM AUTHOR]