Mn-N-C催化剂的制备及其在碱性介质中对氧还原反应的电催化性能

选用壳聚糖(CS)为原料制备了壳聚糖水杨醛席夫碱锰配合物(Mn-CS-sal)。将Mn-CS-sal配合物负载于石墨碳上得到碳载配合物(Mn-CS-sal/C),后经高温热处理得到Mn-N-C目标催化剂(Mn-N-C-t,t=200、400、600、800、1 000℃)。采用FT-IR、XRD、XPS和电化学等方法对催化剂的组成和结构进行了表征,对其在氧还原反应中的电催化性能进行了研究。结果表明,所得到的Mn-N-C催化剂对氧还原反应(ORR)具有很好的催化作用,但以600℃热处理制备的催化剂其活性最好。催化剂中Mn-N-C结构是催化ORR的活性位。采用循环伏安法获得了Mn-N-C-t催化ORR的动力学参数,即总的转移电子数n和电子传递系数αnα;具有最佳活性的Mn-N-C-600催化剂的总转移电子数为3.63,说明在此条件下,Mn-N-C-600催化ORR主要以4e转移途径为主,由此提出了可能的氧还原反应的机理。

Preparation of Mn-N-C catalyst and its electrocatalytic activity for the oxygen reduction reaction in alkaline medium

Chitosan salicylaldehyde Schiff-base manganese complex (Mn-CS-sal) was synthesized by a simple chemical method and then supported on graphite carbon; the graphite-supported Mn-CS-sal (Mn-CS-sal/C) was heat-treated at different temperatures (t) to obtain the Mn-N-C catalysts (Mn-N-C-t, t=200, 400, 600, 800, 1 000 ℃). The electrocatalytic activity of Mn-N-C catalysts in the oxygen reduction reaction (ORR) was investigated and their structure and composition were characterized by Fourier Transform Infrared (FT-IR) spectrum, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results indicated that all the Mn-N-C catalysts are highly active in ORR, whereas the Mn-N-C-600 catalyst heat-treated at 600 ℃ exhibits the highest ORR activity. The excellent ORR activity of the Mn-N-C catalysts in alkaline media should be attributed to their Mn-N-C configuration. Two important kinetic parameters, i.e. the overall ORR electron transfer number (n) and electron transfer coefficiency (αn_α), were determined by the cyclic voltammetry method. The Mn-N-C-600 catalyst shows an overall electron transfer number of 3.63 for ORR, suggesting that the catalytic ORR is via a mixture of 2- and 4-electron transfer pathways, but dominated by the 4-electron transfer process. Based on these observations, a possible mechanism for ORR over the surface of Mn-N-C modified electrode is proposed.