ChemInform Abstract: Room Temperature Electrochemical Redox Reactions of the Defect Perovskite SrFeO_2.5+x.

Abstract

structure structure (solids and liquids) D 2000 47 -011 Room Temperature Electrochemical Redox Reactions of the Defect Perovskite SrFeO 2.5+x . -The electrochemical and chemical oxidation of the defect perovskite SrFeO 2.5 to the cubic perovskite SrFeO 3 at ambient temp. in alkaline electrolyte is shown to be principally reversible. The oxidation occurs via the intermediate phases SrFeO 2.75 , SrFeO 2.87 , and SrFeO 3−δ (0≤δ≤0.003). The structure of the brownmillerite type parent phase is characterized by the presence of stacking faults in the octahedral and tetrahedral sequence of layers whose concentration increases significantly upon formation of the intermediate phases. Tetragonal, cubic, and pseudocubic symmetries can be observed depending on the oxidation rates of the perovskites. -(NEMUDRY, A.; WEISS, M.; GAINUTDINOV, I.; BOLDYREV, V.; SCHOELLHORN, R.; Chem. Mater. 10 (1998) 9, 2403-2411; Inst. Anorg. Anal.

Anion-Based Pseudocapacitance of the Perovskite Library La1–xSrxBO3−δ (B = Fe, Mn, Co)

“…Additionally, BM-SFO has a broad shoulder on the anodic scan that may be attributed to a two phase transitions from BM-SFO to SrFeO 2.75 as the oxide ion intercalation reaction progresses. 34 Figure 3b shows that the LSMO series has two pairs of redox peaks centered at −0.3 and −0.1 V vs Hg/HgO that are attributed to Mn 2+/3+ and Mn 3+/4+ transitions respectively, caused by OH − anion-based intercalation in agreement with our previous results. 15 We note that the LMO capacitance is lower than we reported previously 15 because VC A is used as a conductive support instead of a N-doped mesoporous carbon.…”

“…Comparing the three B-site series, the LSFO samples have the highest peak currents that suggest fast lattice oxygen diffusion rates, which is supported by the LSFO series' high oxygen vacancy concentrations. The redox peaks centered at E 1/2 ∼ −0.8 V vs Hg/HgO are attributed to OH − anion intercalation induced by Fe 2+/3+ and possibly Fe 3+/5+ transitions through Fe 4+ disproportionation as described by Dann et al 33 for x = 0, 0.2 33 and BM-SFO, 34 but LSFO64 shows the presence of a reversible redox peak centered at ∼−0.3 V vs Hg/HgO which is attributed to be the Fe 3+/4+ transition.…”

“…This could be due to its slightly higher oxidation state, shown in Figure S12a and emphasized by the relatively larger anodic shoulder in Figure S14b at ∼0.4 V vs Hg/HgO which could prevent Fe 5+ from being stable. 34 Additionally, all materials demonstrated the diffusion limited capacitance increase with lower scan rates when supported on the CFP at high mass loading. These results emphasize the importance of comparing materials via their surface area-normalized charge capacity in the same cell configuration and designing pseudocapacitors with high vacancy content and high surface area.…”

“…Our results, summarized in Table S2, mostly agree with the LSFO phase diagram 33 with the differences in La 0.2 Sr 0.8 FeO 3−δ (LSFO28) being attributed to its high oxygen vacancy concentration. The orthorhombic phase formations in the x = 0−0.2 and BM-SFO compositions likely result from the predominance 33,34 of Fe 3+ and Fe 5+ that do not cause the Jahn−Teller distortion elongation of the c-axis. However, the ionic radii of these ions in the B-site yield a Goldschmidt tolerance factor less than 0.9, which causes a significant octahedral tilting and distortion of a would-be cubic lattice into an orthorhombic lattice.…”

Tuning Redox Transitions via the Inductive Effect in LaNi1–xFexO3−δ Perovskites for High-Power Asymmetric and Symmetric Pseudocapacitors

“…Nucleation energy barriers to these multiple phase transitions would slow down charge transfer kinetics, 41 thus requiring a large overpotential in both directions toward intercalation that explains the large observed peak separation in BM-SFO. 8 Related work by Nemudry et al 42 has identified the slow phase transformation of SrFeO 2.5 to SrFeO 3 occurring at ∼0.2 V vs Hg/HgO at a 1.5 mA g ox −1 current density. A small hump at x = 2.50 is observed during insertion, occurring at ∼0.4 V vs Hg/HgO, which agrees with Nemudry 42 after considering the iR drop and polarization resistance resulting from the ∼10× higher applied current.…”