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

Abstract

We report the utilization of defect order for development of a bifunctional oxide electrocatalyst. This structure−activity relationship is demonstrated through a disorder−order transformation in LaA 2 Fe 3 O 8 (A = Ca, Sr). The defect-ordered oxide, LaCa 2 Fe 3 O 8 , shows electrocatalytic activity for oxygen evolution reaction, on par with that of the state-of-the-art precious metal catalyst RuO 2 . In addition, it is capable of catalyzing the other halfreaction of water-splitting, namely the hydrogen evolution reaction. Importantly, it is an iron-based catalyst and can be used as a single phase bulk material. The most important aspect of this work is the pronounced impact of defect order on the electrocatalytic properties of oxides.

Experimental correlation of Mn3+cation defects and electrocatalytic activity of α-MnO2– an X-ray photoelectron spectroscopy study

“…212–219 However, herein we employed 0.0709 mF cm −2 for C s corresponding to the areal capacitance of the bare GC disk electrode, that is, the substrate electrode for the preparation of α-MnO 2 -AB thin-film WEs. 17 On the other hand, according to McCrory et al , 157 for metal oxide catalysts in NaOH and KOH solutions C s values ranging from 0.022 mF cm −2 to 0.130 mF cm −2 are reported, 220–232 thus the C s value based on the bare GC disc electrode, that was used in our work, is well within this range. However, since original (untreated) data to all double-layer capacitance measurements is provided in the ESI† to this manuscript, it will be straightforward for other groups to convert to ECSAs based on other C s values, or the specific capacitance of an atomically flat α-MnO 2 surface, which will possibly be determined in a future study, respectively.…”

“…[212][213][214][215][216][217][218][219] However, herein we employed 0.0709 mF cm À2 for C s corresponding to the areal capacitance of the bare GC disk electrode, that is, the substrate electrode for the preparation of a-MnO 2 -AB thin-lm WEs. 17 On the other hand, according to McCrory et al, 157 for metal oxide catalysts in NaOH and KOH solutions C s values ranging from 0.022 mF cm À2 to 0.130 mF cm À2 are reported, [220][221][222][223][224][225][226][227][228][229][230][231][232] thus the C s value based on the bare GC disc electrode, that was used in our work, is well within this range. However, since original (untreated) data to all This journal is © The Royal Society of Chemistry 2022…”

Perovskite Oxides as Electrocatalysts for Hydrogen Evolution Reaction

“…The change in the ionic radius of the A-site cation can sometimes result in a change in the arrangement of oxygen vacancies, which will be discussed later. This was recently observed for La 1/3 Ca 2/3 FeO 3–1/3 , which has an ordered structure with a significantly better HER activity, compared to La 1/3 Sr 2/3 FeO 3–1/3 , which has a disordered structure …”

“…In some perovskite oxides, oxygen vacancies can have an ordered arrangement, which sometimes leads to an enhanced HER activity. In a recent study, La 1/3 Ca 2/3 FeO 3–1/3 , which contains an ordered arrangement of oxygen vacancies (Figure ), showed a HER performance significantly better than that of La 1/3 Sr 2/3 FeO 3–1/3 , where the vacancy distribution is random. Also, both compounds showed a HER performance greater than that for LaFeO 3 , which does not have oxygen vacancies …”

“…The effect of A-site cation on HER activity has been discussed by a number of researchers. − In some cases, the substitution of the A-site cation has led to the enhancement of the electrical conductivity, Goldschmidt tolerance factor, A-site order, etc. There have been efforts to correlate these changes with the HER performance.…”