Cobalt oxide

Analytical grade chemicals were used in this study without any purification. Tetrabutyl titanate ((TBT), Sigma Aldrich), titanium tetrachloride (Alfa Aesar), toluene (99.9%, Sigma Aldrich), ethylene glycol (VWR Chemicals), ethanol, iron(III) chloride hexahydrate (Sigma Aldrich), cobalt chloride hexahydrate (Acros Organics), polyethylene glycol (PEG-8000, Alfa Aesar), sodium acetate (Alfa Aesar), graphite powder (Fisher Chemicals), sulphuric acid (98%, VWR Chemicals), sodium nitrate (Sigma Aldrich), potassium permanganate (Sigma Aldrich), hydrogen peroxide (30%, Alfa Aesar), cobalt oxide (50–80 nm diameter, Alfa Aesar), potassium dichromate (Sigma Aldrich), bisphenol A (Sigma Aldrich) were used in this study.

X-ray absorption spectra were collected at Beijing Synchrotron Facility (BSRF) on beamline 1W1B. The BSRF storage ring is operated at the electron energy of 2.2 GeV with beam current of 250 mA. A Si (111) double-crystal monochromator was applied. The beam size used at the sample position was about 900 × 300 μm². For electrochemical experiments, no transmission data could be collected, and then fluorescence mode was used. All the data were collected at ambient temperature. Curve fitting was performed with Artemis and IFEFFIT software24 32 (link), EXAFS curve fitting of these three spectra was carried out using both Co(OH)₂ and CoOOH data as the starting parameters. Before collecting the XAS spectra, the electrode was cycled 30 times in a three-electrode cell to reach a steady state. In situ electrochemistry was performed in the self-made device (Fig. 1b) and cyclic voltammetry was used from −0.3 to 0.4 V. To meet the condition of XAS sampling, we set the scan rate at 0.4 mV s⁻¹. Spectra were acquired in Quick-EXAFS (QXAS) mode. Cobalt oxide (99.995%, Alfa Aesar, may contain up to 10% Co₃O₄) was purchased to be the reference.

Samarium Oxide (Sm₂O₃, 99.9%. Alfa Aesar), Barium Carbonate (BaCO₃, 99.0%, Alfa Aesar), Calcium Carbonate (CaO, 99.5%, Alfa Aesar), and Cobalt Oxide (Co₃O₄, 99.9%, Alfa Aesar) powder were used for the synthesis of SmBa_1-xCa_xCo₂O_5+d (SBCCO, x = 0.01, 0.03, 0.1, and 0.2) by solid state synthesis (SSR). Each powder was accurately weighed according to its chemical composition, and mixed using an agate mortar with a pestle and ethanol. The mixtures were placed in an oven and maintained at 78°C for 12 h to evaporate the ethanol. Mixtures were calcined for 6 h at 1000°C as a first calcination step to decompose all the carbonate. After that, materials were crushed by the agate mortar with the pestle and ball mill; then, a secondary calcination step was carried out for 8 h in an electric furnace at 1100°C in air atmosphere.
The chemical compositions and abbreviations in SmBa_1-xCa_xCo₂O_5+d (SBCCO, x = 0.01, 0.03, 0.1, and 0.2) of cathode materials are summarized in Table 1.
X-ray diffraction (XRD) patterns of the synthesized SmBa_1-xCa_xCo₂O_5+d (SBCCO, x = 0.01, 0.03, 0.1, and 0.2) oxide systems were obtained on a Model D/Max 2500, Rigaku (45Kv, 200mA, Cu kα radiation); the obtained data were matched with reference data for the phase synthesis and analyzed using the MDI JADE six program.