| Oxygen reduction reaction (ORR) as an important electrochemical reaction is widely used for the electrochemical energy conversion devices and electrolysis technologies including fuel cells, metal-air batteries, water treatment, and chlor-alkali industry. Owing to the complex process of oxygen reduction reaction and sluggish ORR kinetics, precious metal catalysts are still needed to accelerate the ORR and reduce the over potential. Presently, the widely used catalysts for ORR are still Pt-based catalysts. However, the high cost and low storage of the Pt-based catalysts have hindered the commercial application. Therefore, it has important scientific significance and practical value to develop some inexpensive, abundant and stable electrocatalysts to replace Pt-based catalysts.Ag was used as the active component to synthesize a series of Ag-based catalysts in this paper. The Ag-based catalysts were modified through changing the catalyst loading method and controlling the nano structure of MnO2 and carbon support. The physical and chemical characterization of the catalysts were carried out. And we studied the electro-catalytic activit toward ORR of the catalysts in alkaline media.Firstly, different crystal forms and morphologies of MnO2 were prepared by hydrothermal method through controlling the reaction temperature, reaction time, precursor and its concentration. Then, the MnO2 nanowires supported silver nanoparticles was synthesized and then we physical mixed the Ag/a-MnO2 catalyst and carbon support to prepare the Ag/a-MnO2/C catalyst. The results indicated that the Ag/a-MnO2 exhibited better electrochemical activity than MnO2 nanowires. Meanwhile, the ORR activity of the catalyst was significantly improved by the introduction of the carbon support. This phenomenon shows that the conductivity and dispersion of carbon support have great promoting effect on improving the catalytic activity of the catalyst.Secondly, Ag/a-MnO2/C catalyst was prepared by a two steps synthesis method using pre-treated Vulcan XC-72 carbon black as the support. Compared with the Ag/C catalysts, the ORR activity and stability of the Ag/a-MnO2/C is improved significantly. This is mainly due to the a-MnO2 nanowires have excellent activity for hydrogen peroxide decomposition. The result from the RRDE measurements suggest that the H2O2 fractions were only achieved 2.1%, so a quasi four electron reaction pathway took place on the surface of the Ag/a-MnO2/C catalyst.Thirdly, Ag-MnO2/C catalyst was synthesized by a one step thermal calcination method under the protection of inert gases using pre-treated Vulcan XC-72 carbon black as the support. Ag and MnO2 nanoparticles were uniformly loaded on the surface of carbon support. The best catalyst was obtained by adjusting the load ratio of the two kinds of nanoparticles. The results shows that the ORR activity and stability of Ag-MnO2/C catalyst were higher than that of Ag/?-MnO2/C catalyst. This is mainly due to the synergistic effect between Ag and MnO2 nanoparticles to improve the ORR activity of the catalyst.Finally, the prepared ?-MnO2/C catalyst and Ag/C catalyst were prepared by a simple physical mixture and used as catalyst in the catalytic layer of the gas diffusion electrode. The gas diffusion electrode can be effectively used in the oxygen cathode Ion-exchange membrane electrolysis cell. The electrolysis cell test results show that compared with the electrode made of Ag/C catalyst, the hydrogen peroxide yield is lower in the electrolysis process. This gas diffusion electrode could operate for 280 h, so it can achieve the purpose of energy conservation and emission reduction. |
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