Remarkable Oxygen‐Evolution Activity of a Perovskite Oxide from the Ca_2−xSr_xFe₂O_6−δ Series

Abstract

Herein in we report the unprecedented catalytic activity of an iron‐based oxygen‐deficient perovskite for the oxygen‐evolution reaction (OER). The systematic trends in OER activity as a function of composition, defect‐order, and electrical conductivity have been demonstrated, leading to a methodical increase in OER catalytic activity: Ca2Fe2O6−δ<CaSrFe2O6−δ<Sr2Fe2O6−δ. Sr2Fe2O6−δ also has the highest electrical conductivity and a unique type of defect‐order. In conventional experiments using glassy carbon electrode, Sr2Fe2O6−δ shows better OER activity than the current state of the art catalysts, Ba0.5Sr0.5Co0.8Fe0.2O3−δ and RuO2. It also offers a high intrinsic electrical conductivity, which allows it to act as a catalyst without the need for glassy carbon electrode or carbon powder. Pure disks of this material exhibit an outstanding activity for OER, without any additives or need for electrode preparation.

Simple descriptor derived from symbolic regression accelerating the discovery of new perovskite catalysts

“…Apart from the seminal work of ref. 9 , the generality of μ/t can be also confirmed by recent works 30 – 32 as their data reorganized in Supplementary Fig. 4 .…”

The Pivotal Role of s‐, p‐, and f‐Block Metals in Water Electrolysis: Status Quo and Perspectives

“…According to the current research progress, the alkaline‐earth metals are basically introduced into NNTM‐based oxides to modify their OER and/or HER activity. [ 142–167 ] Furthermore, the incorporation of alkaline‐earth metals mainly leads a fundamental role in the following four aspects. [ 145–165 ] i) Tuning the alkaline‐earth metal species in certain oxides can create lattice defects, which dictates a high conductivity and optimized free adsorption energy toward oxygen intermediates; ii) the alkaline‐earth metal species can gradually leach from the catalysts during catalysis, which will in situ leave pores in the phase reconstructed NNTM‐based (oxy)hydroxides catalysts, conducing to the exposure of active sites; iii) they mediate the formation of NNTM‐species with high oxidation state, thus resulting in the improvement of catalytic activity; and iv) the incorporation of some alkaline‐earth metal species into NNTM‐based phase can alter the morphology during synthesis, such as nanosheet, which is beneficial for the accessibility of reactants to surficial NNTM sites during catalysis.…”

“…[ 142–167 ] Furthermore, the incorporation of alkaline‐earth metals mainly leads a fundamental role in the following four aspects. [ 145–165 ] i) Tuning the alkaline‐earth metal species in certain oxides can create lattice defects, which dictates a high conductivity and optimized free adsorption energy toward oxygen intermediates; ii) the alkaline‐earth metal species can gradually leach from the catalysts during catalysis, which will in situ leave pores in the phase reconstructed NNTM‐based (oxy)hydroxides catalysts, conducing to the exposure of active sites; iii) they mediate the formation of NNTM‐species with high oxidation state, thus resulting in the improvement of catalytic activity; and iv) the incorporation of some alkaline‐earth metal species into NNTM‐based phase can alter the morphology during synthesis, such as nanosheet, which is beneficial for the accessibility of reactants to surficial NNTM sites during catalysis. Taking the perovskite oxides (typically, ABO 3‐ x with alkaline‐earth/rare‐earth metal on the A‐site and 3d‐metal cations on the B‐site, herein focuses on the discussion of alkaline‐earth metal on the A‐site) as an example, Bockris and Otagawa first reported their intrinsic electrocatalytic activities in 1984.…”

“…[ 147–149 ] In the last couple of years, researchers paid attention to A‐site atoms and found that the A‐site atoms could also play an indispensable effect in improving the OER activity. [ 150–155 ] Keeping this in mind, Hona and Ramezanipour found that upon gradually changing the Ca/Sr ratio from 1:0 to 0:1, abundant oxygen‐deficiencies were created in perovskite oxide Ca 2‐ x Sr x Fe 2 O 6‐ σ . [ 150 ] These deficiencies were beneficial for the improvement of the electrical conductivity of the compound, greatly expediating the charge transfer during catalysis, and thereby enhancing OER activity in the alkaline media.…”

“…[ 150–155 ] Keeping this in mind, Hona and Ramezanipour found that upon gradually changing the Ca/Sr ratio from 1:0 to 0:1, abundant oxygen‐deficiencies were created in perovskite oxide Ca 2‐ x Sr x Fe 2 O 6‐ σ . [ 150 ] These deficiencies were beneficial for the improvement of the electrical conductivity of the compound, greatly expediating the charge transfer during catalysis, and thereby enhancing OER activity in the alkaline media. Further study by Sankannavar and Sarkar found that the partial substitution of trivalent La by bivalent Ca not only creates much more oxygen vacancies in La 1‐ x Ca x FeO 3‐ σ , but also increase the average oxidation state of iron from Fe 3+ to Fe 4+ , boosting the reaction kinetics for OER alkaline media.…”