Metal-organic frameworks induced robust layered Co(OH)+2 nanostructures for ultra-high stability hybrid supercapacitor electrodes in aqueous electrolyte

摘要

Comparing with intensively studied alpha-Co(OH)(2) with applying on hybrid supercapacitors, alpha-Co(OH)(2) is believed to possess higher electrochemical energy storage performances because of its larger interlayer spacing. However, alpha-phase is always transforming to beta-phase when subject to successive charge-discharge processes with resulting in fast degradation in electrochemical performance. Here, by controlling ZIF-67 hydrolysis with appropriate pH regulating additives, the robust alpha-Co(OH)(2)-A nanostructures are obtained with excellent electrochemical energy storing performances, which present higher specific capacity of 87.1 mAh g(-1)- at 1 A g(-1), excellent rate capability of 77% capacity retention at 20 A g(-1)- and ultra-high cycle stability of over 100% capacity retention over 200, 000 charge-discharge cycles. Through detailed characterizations, such great enhancement is mainly due to the synergistically achieving interlayer crystal water and non-stoichiometric valence states with stable larger interlayer spacing on the robust layered nanostructures. Moreover, the present study also confirms that, instead of most understanding of H+ (de)intercalation, OH- ions significant contributing to pseudocapacitive storage through inserting and reacting with H+ of crystal water and alpha-Co(OH)(2). Thus, the present simple strategy with clear understanding to the energy storage mechanism is beneficial for designing and fabricating mass producible electrode materials of hybrid supercapacitors.