Song Bing-Ye, Yao Sen
Key Laboratory of Thermo-Fluid Science and Engineering of MOE, School of Energy & Power Engineering, Xi'an Jiaotong University, Xi'an, China.
Key Laboratory of New Materials and Facilities for Rural Renewable Energy of MOA, Henan Agricultural University, Zhengzhou, China.
Front Chem. 2020 Apr 28;8:314. doi: 10.3389/fchem.2020.00314. eCollection 2020.
In order to reduce fuel cell material cost and promote its application, it is urgent to develop non-noble metal materials to replace platinum as the cathode catalysts in fuel cells. The cobalt sulfide and nitrogen co-doped carbon (S-Co-N/C) materials with metal-organic frameworks as precursors have shown good oxygen reduction reaction (ORR) catalytic activity. Benefiting from the protection of catalytic active sites by sulfur atoms, the stability and alcohol-tolerance of the S-Co-N/C catalyst can be significantly improved. In order to fully understand the effect of the sulfurization process on the properties of the material, zeolite imidazole frameworks (ZIF)-8, and ZIF-67 are used as precursors to prepare a novel material of S-Co-N/C by using a sulfurization-pyrolysis method. Another S-Co-N/C material by using a pyrolysis- sulfurization method is prepared for comparison. The effects of the sulfurization process in the preparation on the morphology, chemical structure, specific surface area, and ORR catalytic activity of the final material are investigated. The experimental results show that the surface of the S-Co-N/C material tends to be rough due to the sulfurization reaction of the metal elements. The porosity of the material is reduced to some extent due to the remaining Zn elements in the final product. Interestingly, some carbon nanotubes are found to be generated on the surface of the S-Co-N/C material because of the synergistic effect of Zn and Co on the carbon material during the pyrolysis process, which is beneficial to accelerate the adsorption of oxygen on the S-Co-N/C surface and the electron transportation during the oxygen reduction reaction. In addition, the generated CoS during the sulfurization process can further protect the Co elements from agglomeration, which can effectively increase the ORR catalytic active sites in the final material. The S-Co-N/C material prepared by the sulfurization-pyrolysis method performs a superior ORR catalytic activity to the one synthesized by the pyrolysis-sulfurization method.
为了降低燃料电池材料成本并促进其应用，迫切需要开发非贵金属材料来替代铂作为燃料电池的阴极催化剂。以金属有机框架为前驱体制备的硫化钴与氮共掺杂碳（S-Co-N/C）材料表现出良好的氧还原反应（ORR）催化活性。得益于硫原子对催化活性位点的保护，S-Co-N/C催化剂的稳定性和耐醇性可得到显著提高。为了充分了解硫化过程对材料性能的影响，采用硫化-热解法，以沸石咪唑框架（ZIF）-8和ZIF-67为前驱体制备了新型S-Co-N/C材料。同时制备了另一种采用热解-硫化法的S-Co-N/C材料进行对比。研究了制备过程中的硫化过程对最终材料的形貌、化学结构、比表面积和ORR催化活性的影响。实验结果表明，由于金属元素的硫化反应，S-Co-N/C材料的表面趋于粗糙。由于最终产物中残留的锌元素，材料的孔隙率在一定程度上降低。有趣的是，由于热解过程中锌和钴对碳材料的协同作用，在S-Co-N/C材料表面发现生成了一些碳纳米管，这有利于加速氧在S-Co-N/C表面的吸附以及氧还原反应过程中的电子传输。此外，硫化过程中生成的CoS可进一步保护钴元素不发生团聚，从而有效增加最终材料中的ORR催化活性位点。采用硫化-热解法制备的S-Co-N/C材料比采用热解-硫化法合成的材料具有更优异的ORR催化活性。
