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Density functional theory based ab initio calculations are used to investigate the thermodynamic stability, defect formation energies, and electronic properties of isolated neutral and charged vacancies in SrHfO 3 under various chemical environments. We find that cation defects lead the system into a holedoped state, while oxygen vacancies yield defect levels near the conduction band minimum. The partial and full Schottky defect reaction energies and mixed electron hole conduction behavior of SrHfO 3 is also evaluated. Furthermore, various cases for neutral oxygen vacancy clustering are examined for tuning the electrical properties of oxygen deficient SrHfO 3 . We show that ordered oxygen vacancies in HfO layers are energetically favorable and induce metallicity in this system which emerges due to charge transfer between the vacancy site and the hafnium dangling bond.

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Summary A supercapattery is a device that combines the benefits of supercapacitors' superior power density and cycle stability with the advantages of batteries' higher energy density. We used a simple hydrothermal method to synthesize nickel sulfide (NiS), silver sulfide (Ag2S), and nickel silver sulfide (NiAg2S). The NiS and Ag2S were combined in the best 50/50 weight ratio and found that the specific capacity for NiAg2S is 571.2 C/g which is higher as compared to individual NiS and Ag2S 305.2 C/g and 364 C/g, respectively. Even at 2 A/g, more than 69% of the specific capacity is retained. For asymmetric device fabrication (NiAg2S//AC), the activated carbon was selected as a negative electrode, while NiAg2S was chosen as a positive electrode. A specific capacity of 130.4 C/g was achieved with this device. Energy density for NiAg2S was observed to be 28.97 Wh/kg having a power density of 640 W/kg. To investigate stability, a durability test was performed by subjecting this device to 1000 charging/discharging cycles, which maintain 86% of the initial capacity. Our findings suggest that a mixture of nickel and silver sulfide having a 50/50 weight ratio functioning as an electrode material for supercapattery applications may be more appropriate.

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