Attenuating a metal–oxygen bond of a double perovskite oxide via anion doping to enhance its catalytic activity for the oxygen reduction reaction

Abstract

<p>F-doping promotes the diffusion and surface adsorption process of oxygen at the cathode, and the reaction kinetics have been significantly improved.</p>

Enhanced Electrochemical Performance of the Fe-Based Layered Perovskite Oxygen Electrode for Reversible Solid Oxide Cells

“…To evaluate the impact of Zr 4+ doping on oxygen vacancy formation and migration, the O 1s X-ray photoelectron spectrum was collected to analyze the surface oxygen species. As shown in Figure b, the O 1s spectrum can be deconvoluted into three peaks, located at ∼528.45, 531.04, and 533.29 eV, corresponding to the lattice oxygen (O lat ) in the perovskite, oxygen species absorbed on the surfaces (O abs such as H 2 O, O 2 , and so forth), and physically adsorbed oxygen due to hydroxyl (OH – ) species, respectively . The ratio of O abs /(O abs + O lat ) increased relatively (Table S3), indicating the formation of more oxygen vacancies and the presence of more important active sites for the O 2 adsorption/dissociation after doping Zr 4+ .…”

Halide-Doping Effect of Strontium Cobalt Oxide Electrocatalyst and the Induced Activity for Oxygen Evolution in an Alkaline Solution

“…However, the O 1s spectrum of the parent Sr 2 CoO 4 catalyst (Figure 4d) can only be fitted by two peaks that are assigned for O 2− anion (peak 1) and O 1− /O chem (peak 2), possibly because of a small amount of chemically adsorbed oxygen species. From the data in Table 2 and upon the incorporation of halide ions, the overall peaks' binding energy is shifted to lower values in the order F − > Cl − > Br − which indicates a weaker Co-O bonding due to withdrawn the electron density away from the Co-atom, consequently enhances the lattice oxygen (O 2− ) reactivity and reduces the activation energy required for O 2− activation [47][48][49]…”

“…To gain more insight on the enhanced OER activity of the oxyhalide catalysts, Tafel plots were used to examine the catalysis kinetics for the OER and are plotted in Figure 5c as extracted from the LSV shown in Figure S2 (Supporting Information) that performed at a scan rate of 10 mV s −1 and rotation rate of 1600 rpm. The Tafel plots describe the relationship between the overpotential and the logarithm of the current (I), which can provide important information about water oxidation including the electronic and geometric enhancement in the activity of the electrocatalyst [49]. As shown in Electrochemical impedance spectra (EIS) analysis was also employed to evaluate the charge carrier transfer resistance during the OER for the oxyhalide catalysts of Sr 2 CoO 3 F, Sr 2 CoO 3 Cl, and Sr 2 CoO 3 Br compared to pristine Sr 2 CoO 4 catalyst.…”

“…In contrast, Sr2CoO3Cl, Sr2CoO3Br, and Sr2CoO4 suffer reduced activity and the current density decreased from 44.8 to 35 mA cm −2 , 32.2 to 24.6 mA cm −2 , and 18.3 to 7.5 mA cm −2 , respectively, after only 4 h or less during electrolysis. Presumably, during the longterm stability test in alkaline solution and under applied potential, the halide-doped strontium cobalt oxide catalysts are partially converted to oxyhydroxides due to the intercalation of OH − groups with the fluoride-doped catalyst having the most stable O 2− /OH − /F − coordination and bonding with Co atom due to the stronger electron affinity of fluoride ion [48,49]. However, more work is required to understand the oxyhalide catalysts' struc- In contrast, Sr 2 CoO 3 Cl, Sr 2 CoO 3 Br, and Sr 2 CoO 4 suffer reduced activity and the current density decreased from 44.8 to 35 mA cm −2 , 32.2 to 24.6 mA cm −2 , and 18.3 to 7.5 mA cm −2 , respectively, after only 4 h or less during electrolysis.…”

“…Moreover the O 1s fitted peaks' area ratio of [O 1− /O 2− ] as well as the [(O 1− + O chem )/O 2− ] / O 2− ] were much higher in case of Sr 2 CoO 3 F (3.1, 13.20) than for Sr 2 CoO 3 Cl (2.9, 3.83), Sr 2 CoO 3 Br (1.28, 1.91)and the parent Sr 2 CoO 4 (0.63, 0.63) catalysts, respectively. Therefore, the doping of halide ions particularly fluoride ion enhanced the O 1− and O chem site concentration that directly related to the density of the surface oxygen vacancy defects[48,49].…”