Zero-Dimensional Ordered Sr₂CoMoO_6-δ Double Perovskite as High-Rate Anion Intercalation Pseudocapacitance

Abstract

In quest of a stable structure throughout redox reactions, an approach of B-site ordering (0D arrangement) of cations in double perovskites is adopted. Here, we report B-site cation ordering in double perovskite Sr 2 CoMoO 6-δ (DP-SCM) that tends to a favorable rock salt structure (0D arrangement). The synergy of Co/Mo having good redox ability further facilitates high oxygen mobility. A high content of oxygen vacancy examined using XPS and EPR facilitates a high oxygen anion diffusion rate (2.03 × 10 −11 cm 2 s −1 ). Moreover, fast kinetics (ΔE P ≈ 0.013 V@ 1 mV s −1 ) of charge storage prohibits any phase transformation reflecting the excellent cycle life (125% retention up to 5000 cycles). Such fast kinetics is majorly furnished from anion intercalation with little involvement from double layer mechanism (C dl ≈ 42.1 F g −1 ). DP-SCM achieves a resultant capacitance of 747 F g −1 @ 1 A g −1 with a rate capability of 56% up to 10 A g −1 . Motivated by outstanding performance of DP-SCM electrodes, a symmetric cell is assembled with a 1.4 V operating potential that delivers a high energy density of 64 Wh kg −1 @855 W kg −1 . This work on double perovskites suggests that the advance understanding of cation ordering and charge storage mechanism can provide a new direction to fabricate highly capacitive electrode materials.

Advances and Perspectives for the Application of Perovskite Oxides in Supercapacitors

“…With the synergistic redox effect of Co and Mo ions with the mechanism shown in Figure c, the material obtained exhibited good electrical capacity. As illustrated in Figure d, it exhibited higher capacitance in the KOH electrolyte than the KNO 3 electrolyte, highlighting the superiority of the oxygen anion intercalation mechanism in the alkaline electrolyte . Therefore, ordered double perovskite oxides are more suitable as active materials for supercapacitors.…”

“…In addition, substitution of A- or B-site elements can make a single perovskite oxide turn into double perovskite oxides with an ordered structure. Also, double perovskite oxides can be converted from ABO 3 under a reduced atmosphere. , The double perovskite oxides, such as La 2 CoMnO 6 , Y 2 NiMnO 6 , Ba 2 Bi 0.1 Sc 0.2 Co 1.7 O 6 , PrBaMn 2 O 6 , Sr 2 CoMoO 6 , etc., were intensely probed in SCs. ,,,, Among them, PrBaMn 2 O 6 with the A-site cation ordered structure was converted from Pr 0.5 Ba 0.5 MnO 3−δ under a H 2 atmosphere and Ba 2 Bi 0.1 Sc 0.2 Co 1.7 O 6 and Sr 2 CoMoO 6 with the B-site cation ordered structure were synthesized in air conditions. ,− Specially, a doubly ordered perovskite oxide (AA′BB′O 6 ) with A/A′ cation order and B/B′ cation order was first reported by NaLaMgWO 6 . These ordered structures in perovskite oxides facilitate the accommodation of a greater concentration of oxygen vacancies because the metal ions are in the lower valence state.…”

“…In comparison to single perovskite oxide, double or triple perovskite oxide with abundant metal ions has high adjustability. Many reports were about the potential or successful application of double perovskite (AA′BB′O 6 ) as the electrode material for SCs. ,,− ,,,− In addition to the internal tuning of a simple double perovskite, further modifications can be made to its surface area.…”

“…However, the crystal structure of perovskite may be destroyed as a result of the leaching of cations in the aqueous electrolyte for a single perovskite oxide. , Fortunately, the double perovskite and triple perovskite oxides with a mixed arrangement of different ions have a more stable structure, thus enhancing the electrochemical stability of SCs . In addition, there are wider voltage windows for them, increasing the energy density of SCs according to the calculation formula of energy density, E = 1/2 CV 2 , where C and V refer to the specific capacitance and potential window of the working electrode, respectively, and also show the application potential in SCs. − Specially, the lattice elements of a simple double perovskite oxide (AA′B 2 O 6 ) are chaotically distributed, while it could turn to an ordered structure with a uniform distribution of A-site cations under reducing conditions. − The internal ordered structure in double perovskite oxides brings faster oxygen kinetics than the disordered structure in the field of solid oxide fuel cells. ,, For SCs, the ordered structure is in favor of the concentration of oxygen vacancies. Two main kinds of double perovskite oxides, PrBaMn 2 O 6 and Sr 2 CoMoO 6 , have been studied as the electrode material, ,,,− while PrBaMn 2 O 6 shows the A-site ordered layered structure and Sr 2 CoMoO 6 shows the B-site ordered layered rock-salt structure. , As described, the internal ordered structure can provide more oxygen vacancies and a convenient electron transmission path than the disordered counterpart.…”

Cobalt-Based Layered Hydroxides with Modulated Electronic and Thermodynamic Properties for High-Performance Supercapacitors

“…Mechanism studies demonstrate that ions can only migrate within the double-layer area of electrolytes and be adsorbed toward the surface-to-subsurface part of the electrodes. Hence, this charging/discharging mechanism limits the loading mass of active materials, since the ions cannot easily penetrate into the electrode. − To address this issue, later studies introduced redox reactions that happened onto transition metal oxides/hydroxides with layered/channeled structures to employ additional electron transfer as well as electric field driving intercalation pseudocapacitance. − For an ideal intercalation pseudocapacitive electrochemical process, ions in the aqueous electrolyte can migrate into the electrode with lower resistance, which makes full usage of these materials …”