Tuning Redox Transitions via the Inductive Effect in LaNi_1–xFe_xO_3−δ Perovskites for High-Power Asymmetric and Symmetric Pseudocapacitors

Abstract

We have synthesized a series of LaNi 1−x Fe x O 3−δ (LNF; x = 0, 0.15, and 0.55) perovskites along with brownmillerite−SrFeO 2.5 (BM-SFO) to utilize Ni's high electronegativity combined with the inductive effect via iron substitution to make higher voltage anion-based symmetric and asymmetric pseudocapacitors. The materials' structures were well characterized, and their electrochemical performance was evaluated using cyclic voltammetry (CV) and galvanostatic charging and discharging (GCD) tests in 1 M KOH. We found that substituting Ni for Fe in the B site increased the Ni 2+/3+ redox to higher potentials while the Fe 3+/4+ redox peaks shifted to lower potentials due to the inductive effect. The LNF materials displayed a surface anion-redox pseudocapacitance mechanism as opposed to a pseudocapacitive intercalation mechanism that enabled a LaNi 0.45 Fe 0.55 O 3−δ (LNF55) symmetric pseudocapacitor to discharge with high power (250 000 W kg −1 ) at an energy density of 4.3 Wh kg −1 . It had the largest discharge peak (1 V) for any symmetric anion-based pseudocapacitor reported to date. The BM-SFO//LNF55 asymmetric pseudocapacitor had a 1.8 V potential window and the largest discharge voltage at 1.1 V of any anion-based pseudocapacitor reported to our knowledge, yielding an energy density of 19.5 Wh kg −1 at a power density of 394 W kg −1 .

Electrochemical Evolution of Pore-Confined Metallic Molybdenum in a Metal–Organic Framework (MOF) for All-MOF-Based Pseudocapacitors

“…Thus, various kinds of redox-active thin films with nanostructures have been utilized in pseudocapacitors. 4,5 Common materials for pseudocapacitors that have been reported to show promising performances include manganese oxide, 6 cobalt oxide, 7,8 nickel oxide, 3,9 vanadium oxide, 10 and conducting polymers, 11 but most of them can only be used as materials for the positive electrodes in supercapacitors. Recently, molybdenum oxide has been reported as a material for negative electrodes in supercapacitors and found to exhibit promising pseudocapacitive behavior in aqueous electro-lytes.…”

“…As the charging and discharging processes of pseudocapacitive materials rely on the fast and reversible Faradaic reactions of redox-active thin films deposited on the electrode surface, , to achieve a high capacitance, the design of redox-active thin films with high surface area is desirable; with more redox-active sites exposed on the surface that can be involved in electrochemical reactions, a higher specific capacitance of the same material can be achieved. Thus, various kinds of redox-active thin films with nanostructures have been utilized in pseudocapacitors. , Common materials for pseudocapacitors that have been reported to show promising performances include manganese oxide, cobalt oxide, , nickel oxide, , vanadium oxide, and conducting polymers, but most of them can only be used as materials for the positive electrodes in supercapacitors. Recently, molybdenum oxide has been reported as a material for negative electrodes in supercapacitors and found to exhibit promising pseudocapacitive behavior in aqueous electrolytes. − Therefore, the design of molybdenum-based redox-active thin films possessing high surface area becomes highly desirable for developing negative electrodes in pseudocapacitors with enhanced performances.…”

Pseudocapacitive Energy Storage and Electrocatalytic Hydrogen-Evolution Activity of Defect-Ordered Perovskites SrxCa3–xGaMn2O8 (x = 0 and 1)

“…Since then, some other pseudocapacitive materials based on oxygen anion intercalation have been studied. Examples of the materials that have been investigated are La 1– x Sr x MnO 3 , ,, La 1– x Ca x MnO 3 , SrCo 0.9 Nb 0.1 O 3 , and LaNi 1– x Fe x O 3−δ . The compounds studied before have been primarily perovskite-based oxides, ABO 3 , where the A or B sites were occupied by two cations that were distributed randomly.…”

“…Figure shows the CVs of Ca 3 GaMn 2 O 8 and SrCa 2 GaMn 2 O 8 in the three-electrode setup at varying scan rates of 5, 20, 40, 60, and 80 mV/s in the voltage range of 0.4 to −1.0 V vs Ag/AgCl. The quasi-rectangular CV shapes indicate pseudocapacitive behavior, and Mn 2+ /Mn 3+ and Mn 3+ /Mn 4+ redox peaks are indicative of the Faradaic processes. ,− , …”

“…In recent years, material discovery efforts have also been directed to finding new materials for intercalation-based pseudocapacitors, in particular those involving oxygen ion intercalation, which was first shown in Nd 1– x Sr x CoO 3 . A number of oxide materials including LaMnO 3 , La 1– x Sr x MnO 3 , ,, La 1– x Ca x MnO 3 , SrCo 0.9 Nb 0.1 O 3 , and LaNi 1– x Fe x O 3−δ have been studied for oxygen anion intercalation.…”