Xie Yan, Tang Chizhou, Hao Zhiqiang, Lv Yang, Yang Ruixia, Wei Xuming, Deng Weiqiao, Wang Anjie, Yi Baolian, Song Yujiang
School of Chemical Engineering, Dalian University of Technology, Dalian 116024, P.R. China.
Faraday Discuss. 2014;176:393-408. doi: 10.1039/c4fd00121d. Epub 2014 Nov 14.
The scarcity and high cost of Pt-based electrocatalysts for the oxygen reduction reaction (ORR) hinder the practical application of proton exchange membrane fuel cells (PEMFCs). It is critical to replace platinum with non-noble metal electrocatalysts (NNMEs). Carbonized metalloporphyrins represent an important class of NNMEs, but most metalloporphyrins are costly and the corresponding NNMEs do not possess a high ORR activity. Herein, we report that the self-assembly of inexpensive hemin leads to porous nanomaterials in water under ambient conditions and subsequent heat-treatment of the unprecedented nanoporous hemin results in a magnetic NNME with a much enhanced ORR activity compared with directly carbonized hemin without self-assembly. The improvement of the ORR activity likely originates from the exposure of more ORR active sites, caused by the surface area increase of the nanoporous hemin after carbonization over that of micro-scale pristine hemin crystals. Moreover, the ORR activity of heat-treated nanoporous hemin is actually comparable to that of commercial Pt/C in alkaline solution. Additionally, the carbonized nanoporous hemin is much better than commercial Pt/C in terms of durability and tolerance to methanol. This study opens up a new avenue to the production of inexpensive metalloporphyrin-based NNMEs with a high ORR performance by using a self-assembly method in combination with traditional pyrolysis.
用于氧还原反应（ORR）的铂基电催化剂的稀缺性和高成本阻碍了质子交换膜燃料电池（PEMFC）的实际应用。用非贵金属电催化剂（NNME）替代铂至关重要。碳化金属卟啉是一类重要的NNME，但大多数金属卟啉成本高昂，相应的NNME不具备高ORR活性。在此，我们报道了廉价的血红素在环境条件下于水中自组装形成多孔纳米材料，随后对前所未有的纳米多孔血红素进行热处理，得到一种磁性NNME，与未自组装直接碳化的血红素相比，其ORR活性大大增强。ORR活性的提高可能源于碳化后纳米多孔血红素的表面积比微米级原始血红素晶体的表面积增加，从而暴露出更多的ORR活性位点。此外，在碱性溶液中，热处理后的纳米多孔血红素的ORR活性实际上与商业Pt/C相当。此外，碳化的纳米多孔血红素在耐久性和对甲醇的耐受性方面比商业Pt/C要好得多。这项研究通过将自组装方法与传统热解相结合，为生产具有高ORR性能的廉价金属卟啉基NNME开辟了一条新途径。
