Superior Bifunctional Electrocatalytic Activity of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3‐δ/Carbon Composite Electrodes: Insight into the Local Electronic Structure

Abstract

By using X-ray absorption near edge structure spectroscopy (XANES), changes in the local electronic structure of the perovskite have been observed when a composite perovskite/ carbon electrode is developed. This fi nding provides a novel understanding of perovskite/carbon composite electrodes and thus opens new perspectives for the optimization of the composite electrodes or for tailoring new perovskite compositions. Furthermore, our results also indicate that the electrode preparation process can deeply change the perovskite electronic structure. This should be always carefully taken into account in order to develop a proper electronic structure/catalytic activity correlation for this class of compounds.The selected perovskite composition for this study is Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF) since this perovskite has already been shown to be a promising bifunctional catalyst (i.e., high ORR and OER activity) in combination with carbon but not as a single perovskite catalyst. [ 6,7,[14][15][16]20 ] BSCF was prepared by a sol-gel combustion method, and after calcination at 1000 °C for 2 h, phase formation was confi rmed by X-ray diffraction analysis (Supporting Information, Figure S1). Acetylene black carbon was treated in nitric acid at 80 °C overnight in order to create surface oxygen-containing functional groups that were shown to improve and stabilize the AB catalytic activity in alkaline environment. [ 14 ] The electrodes were prepared by ultrasonicating BSCF or BSCF and acetylene black (AB; 5:1 weight ratio) in isopropanol and Na + -modifi ed Nafi on as a binder; then optimized thin porous fi lms were deposited on glassy carbon substrates that allow investigating electrochemical activity of the material by the thin fi lm rotating disk electrode (RDE) technique. [ 21 ] The ORR and OER currents for the BSCF and the BSCF/AB electrodes are shown in Figure 1 . For both reactions, the composite BSCF/AB electrode shows a signifi cant lower overpotential compared to the BSCF electrode. Regarding the ORR, the BSCF/AB composite electrode shows a decrease in the overpotential (130 ± 10 mV at −0.025 mAcm geo −2 ) and an increase in the reduction current over the whole ORR potential range compared to the BSCF electrode. As found previously by rotating ring disk electrode (RRDE) measurements, adding carbon to BSFC electrodes can also signifi cantly infl uence the reaction pathway transitioning from mainly hydroperoxide as product (two-electron reduction) on the BSCF and the carbon single material electrodes, to almost complete O 2 reduction to water on the BSCF/AB composites. [ 14 ] Also in case of the OER, the BSCF/AB composite electrode displays a signifi cant higher activity compared to the BSCF electrode. At the value of 10 Ag metal −1 the BSCF/AB composite electrodes display a quasi steady-state potential of 1.55 ± 0.012 V (RHE), about 100 mV lower than the BSCF single material Perovskite oxides have been investigated for a wide range of applications, and recently they have gained attention as oxygen electrocata...

Recent Advances in Carbon‐Based Bifunctional Oxygen Electrocatalysts for Zn−Air Batteries

“…The important role of electrical coupling in enhancing bifunctional oxygen catalysis for the ORR/OER has been well clarified by Fabbri and co‐workers . The authors selected individual Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3‐δ (BSCF) and acetylene black carbon supported BSCF (BSCF/AB).…”

“… XANES spectra at Co K‐edge for BSCF and BSCF/AB electrode, inset shows OER and ORR polarization curves of various catalysts . Copyright 2015, Wiley‐VCH.…”

Design of Efficient Bifunctional Oxygen Reduction/Evolution Electrocatalyst: Recent Advances and Perspectives

“…[49,50] Perovskite oxides (ABO 3 ) are also widely investigated as bifunctional ORR/OER catalyst in alkaline electrolytes. [21,[51][52][53][54][55][56][57][58] Their compositions and properties can be finely tuned by partially substituting A and B with other metal components. Typically, A-site mainly influences on the capability of oxygen adsorption, and B-site mainly influences on the activity of the adsorbed oxygen.…”

A Composite Catalyst Based on Perovskites for Overall Water Splitting in Alkaline Conditions

“…[1,2] Thus, electrochemical water splitting has attracted attentions due to its low energy consumption and high-purity products. [7][8][9][10][11][12][13] Recently, for the compositional flexibility, the exsolution approach based on the crystal reconstruction of perovskite under reducing atmosphere has been considered for building nanoparticles and perovskite composite materials. [5,6] Therefore, tremendous efforts have been devoted toward developing active catalysts to accelerate their chemical kinetics.…”