Composite Electrode Boosts the Activity of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ Perovskite and Carbon toward Oxygen Reduction in Alkaline Media

Abstract

Herein we report the electrochemical activity and selectivity toward the oxygen reduction reaction (ORR) for composite electrodes made of Ba0.5Sr0.5Co0.8Fe0.2O3‑δ (BSCF) perovskite oxide and Acetylene black (AB) carbon in alkaline media. The onset potential and the selectivity, i.e., hydroperoxide formation, toward the ORR exhibit a volcano type behavior as a function of the electrode composition. The HO2 – formation measured by rotating ring disk electrode technique decreases from about 60% and 70% for the BSCF and the AB, respectively, to 28% for the electrode having a BSCF/AB weight ratio of 1.25 (values taken at 0.4 V vs RHE). Accordingly, the value for the overall transferred electrons is significantly larger (around 3.5) for the composite electrode compared to individual materials. Therefore, the overall results point toward a beneficial interaction between BSCF and AB. Different scenarios are considered; first an improved electrical connection of BSCF particle agglomerates upon carbon addition. However, the latter cannot fully explain the significant improvement in ORR activity and selectivity for the composite electrodes. By measuring the BSCF electrochemical activity toward HO2 – reduction, we can exclude the occurrence of a synergistic ORR process where oxygen is first reduced on AB to OH2 –, and then further electroreduced to OH– by the BSCF. Besides the activity toward hydroperoxide electroreduction, the potential of BSCF as catalyst for the hydroperoxide disproportionation reaction is also investigated, and even though a certain catalytic activity exists, the perovskite oxide shows rather low decomposition rate. These results might suggest that ligand (electronic) effects between the two materials also play a role in the enhanced ORR activity of the composite electrodes.

Electrocatalysis of Perovskites: The Influence of Carbon on the Oxygen Evolution Activity

“…We have previously shown enhanced activity of BSCF towards the ORR 31,32,33 and OER 32 when AB f is present and further extend the study to the perovskite oxides LSCF and PBCO using a typical oxide to carbon weight ratio of 5:1. New insights towards the study of these materials with and without the addition of carbon for the OER have been achieved by performing thin-film RDE measurements in alkaline media.…”

Perovskite Electrocatalysts for the Oxygen Reduction Reaction in Alkaline Media

“…The hydroperoxide could be subsequently catalyzed to hydroxide, resulting in an apparent transfer of four electrons per reduced O 2 . This is a likely scenario for many perovskite electrodes, particularly for composite electrodes containing carbon [92,95,96,[137][138][139]. The side-on mechanism in Figure 6b requires that the O-O bond breaking in step b2 is not limiting.…”

“…The most active composite electrodes [22] are also included for reference. The currents of the composites are equal or higher than those of the single crystalline surfaces because carbon can act as a co-catalyst [92,95,[137][138][139] and disperses the catalyst [92,93].…”

Superior Bifunctional Electrocatalytic Activity of Ba0.5Sr0.5Co0.8Fe0.2O3‐δ/Carbon Composite Electrodes: Insight into the Local Electronic Structure

“…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 electrocatalysts for application in low-temperature alkaline fuel cells and electrolyzers.…”

“…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 .…”