| Hydrogen is thought to be the most efficient, clean and renewable energy. Among several hydrogen production techniques, electrolysis of water is one of the most promising methods. However, the efficiency of this process is severely limited by the kinetics of the oxygen evolution reaction(OER). Therefore, great efforts have been made in finding an efficient electrocatalyst for the OER. The OER is a particular challenge, with few materials(noble metal oxides) showing significant activity for this reaction. Cobalt-based catalysts are one of the few non-noble metal catalysts which show good catalytic activity and stability for water oxidation in alkaline solution. These materials, however, generally show high overpoetntials towards OER, which is mainly due to the OER inertia and the poor conductivity of these non-noble metal oxides. In addition, the high content of noble metals in the catalysts enhace the cost of the materials.In order to overcome the two the above-mentioned shortcomings in the present catalysts, two main work on the improvement of the activity of the Co-based catalyst and high cost of high irdium content Ti/IrOx-Sb2O5-SnO2(Ir:Sb:Sn = 10:10:80, it was also named as Ti/ISS) electrode OER catalysts were conducted in this paper.(1) Prearation of CoFe2O4/CoFex@NC catalyst from in-situ pyrolysis of a single source precursor([Co(H2O)6)][Fe(HEDTA)Cl]2ยท4H2O) in nitrogen atmosphere, which was synthesized from aqeous solution containing CoCl2, FeCl3 and H4edta(H4edta = ethylenediaminetetraacetic acid) in a exact molar ratio. The effects of calcination temperature and atmosphere on the morphology, structure and oxygen evolution property of as-prepared CoFe2O4/CoFex@NC catalysts were also studied; and(2) Ti/CoOx-IrO2-Sb2O5-SnO2 anodes fabricated by coating a solution containing of the mixed metal chloride on Ti substrate followed by a simple thermal treatment were developed, for the decrease of the cost and the enhancement the electrocatlytic activity and stability towards OER of the Ti/ISS anode, which is extensively investigated in previous literatures as a anode for OER.Based on the above-mentioned results, it was concleded that:(1) It was found that the catalyst prepared at 600 oC under N2 had the best electrocatalytic properties for oxygen evolution, by exploring the effect of calcination temperature on the acitivity towards OER;(2) The CoFe2O4/CoFex@NC prepared under N2 at 600 oC have larger surface area and better electrocatalytic activity than CoFeOx prepared under air;(3) Cobalt partial-substitution iridium of Ti/ISS anode shows an enhanced oxygen evolution activity in acid and basic aqueous solution. For Ti/C5 ISS anode, small overpotentials of 0.438 and 0.498 V are needed under a current density of 10 and 100 mA cm-2, respectively in 0.5 M KOH aqueous solution, with a corresponding Tafel slope of 55 mV dec-1. Furthermore, the Ti/C5 ISS performs remarkably lower overpotential and Tafel slope than Ti/C0 ISS and Ti/Co3O4 and exhibits much more stable than Ti/C0 ISS and Ti/Co3O4 at high current density in alkaline solution. The significant enhacement of the catalytic performance and stability of Ti/C5 ISS electrode were attributed to its the synergistic effects of cobalt and iridium, resulting in lower OER barriers and higher reaction driving force, good charge transfer ability derived from the enhance of the electronic conductivity and increased number of highly oxidative oxygen species O22-/O-, which were demonstrated by the XPS and EIS testing results. |
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