Pseudocapacitive Energy Storage and Electrocatalytic Hydrogen-Evolution Activity of Defect-Ordered Perovskites Sr_xCa_3–xGaMn₂O₈ (x = 0 and 1)

Abstract

The diverse range of possible arrangements of oxygen vacancies in oxygen-deficient perovskites results in a variety of structure types and fascinating electrochemical properties. Here, we report Ca 3 GaMn 2 O 8 and SrCa 2 GaMn 2 O 8 , where the ordering of oxygen vacancies leads to cation and polyhedral order, resulting in a remarkable array of electrochemical properties coexisting in the same compound. Neutron and X-ray diffraction have been utilized to study the structure of these materials that feature simultaneous defect order and cation order. Remarkably, both materials show very high electrocatalytic activity for hydrogen-evolution reaction (HER) of water splitting in bulk form, without the need for composite formation or nanofabrication. The HER overpotential required to achieve a current density of 10 mA/cm 2 is as low as η 10 ≈ −315 mV. In addition, detailed pseudocapacitive studies show that both compounds are capable of energy storage as anion-based pseudocapacitors, arising from oxygen ion intercalation. The symmetric pseudocapacitor cells fabricated based on these materials show a combination of high energy density and power density. These pseudocapacitor cells are also extremely stable, maintaining their high activity over 1000 cycles of charge−discharge. Electrical charge-transport studies indicate that these compounds have semiconducting properties in a wide temperature range, 25− 800 °C. Magnetic studies using both magnetometry and neutron scattering indicate a transition to an antiferromagnetic state, with a G-type arrangement of spins, where the moment on each Mn is aligned antiparallel to all nearest neighbors. This combination of properties indicates the great potential of this class of defect-ordered systems and their importance to energy research.

Layered Oxides SrLaFe1‐xCoxO4‐δ (x=0–1) as Bifunctional Electrocatalysts for Water‐Splitting

“…As shown in Figure 5a, the acidic HER overpotential values at 10 mA cm −2 , η 10 , are 0.730 V, 0.570, and 0.547 V for SrLaFeO 4 , SrLaCo 0.5 Fe 0.5 O 4 , and SrLaCoO 4‐δ , respectively. Clearly, these overpotentials are not as low as those of highly active catalysts, such as Pt/C (less than 0.1 V) [5,46–48] . However, the systematic trend among the three materials is noteworthy.…”

“…Some of these catalysts, such as BSCF, have shown great promise, particularly for OER [2] . Our group has recently reported several oxide electrocatalysts for both half‐reactions of water splitting [3–7] …”

Bifunctional Water-Splitting Electrocatalysis Achieved by Defect Order in LaA2Fe3O8 (A = Ca, Sr)

“…Oxide materials, especially perovskite-type oxides, can be excellent candidates for application as electrocatalysts due to their stability and high degree of tunability. Several materials from this family have shown significant OER activity. − The HER activity of perovskite oxides is less common, but some materials from this family have been studied for HER catalysis. − However, perovskite oxides that can catalyze both OER and HER are rare, especially in bulk form without nanofabrication or composite formation …”

Advances and Perspectives for the Application of Perovskite Oxides in Supercapacitors

“…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.…”