Atomic-level Structure Engineering Of CoO Nanorods For Oxygen Intercalation Pseudocapacitance And Zinc–Air Batteries

Electrochemical energy storage and conversion devices in terms of supercapacitors and zinc-air batteries have demonstrated great potential in solving the future energy crisis due to high energy conversion efficiency,portability,and safety.However,there are still large gaps in high energy density and power density simultaneously to meet practical applications.Through the surface engineering,we regulate the transition metal oxide,CoO,to improve its performance for oxygen intercalation pseudocapacitance and zinc–air batteries.The specific results and innovation are as follows:Firstly,the gas phase cation exchanged CoO nanorods are exposed to the（111）crystal plane rich in oxygen vacancies,and the oxygen vacancies are concentrated at the surface of 2³ nm.The synthesized Zn_xCo_1-xO nanorods can achieve uniform atomic-level Zn doping.In addition,the confinement of abundant O-vacancies on{111}nanofacets with3%lattice expansion and a high oxygen diffusion concentration gradient,enables easy intercalation of oxygen ions into this oxide with low energy barrier,and the atomically uniform Zn doping assures fast electrical conduction,which change its dominant charge storage mechanism from surface redox reactions to ion intercalation into bulk material and increase its capacity almost to the theoretical limit.The resultant Zn_xCo_1-xO exhibits high-rate performance with capacitance up to 450 F g^-1 at a scan rate of 1 V s^-1.A symmetric device assembled with Zn_xCo_1-xO achieves an energy density of 67.3Wh kg^-1 at a power density of 1.67 kW kg^-1,which is the ever highest value reported for symmetric pseudocapacitors.At last,assembled aqueous zinc-air works smoothly with a high open-circuit of1.43 V.The CoO NRs electrode delivers a voltage of up to 1.25 V at the current density of 10 mA cm^-2,which is higher than that of Pt/C+RuO₂ electrode（1.21 V）.The battery equipped with CoO NRs shows very stable charging（1.89 V）and discharging（1.09 V）voltages at charge current densities of 2 mA cm^-2 and discharge current densities of 20mA cm^-2,which are better than Pt/C+RuO₂ based battery.Moreover,the CoO NRs based battery exhibits 60 stable charge-discharge cycles without noticeable degradation of performance.We fabricate an electronic cell with four Zn-air batteries in series to power 14 parallel blue light emitting diodes（LEDs）,which can reach a voltage as high as 5.17 V.