ZIF-67/石墨烯复合物衍生的氮掺杂碳限域Co纳米颗粒用于高效电催化氧还原

Pyrolysis of ZIF-67/Graphene Composite to Co Nanoparticles Confined in N-Doped Carbon for Efficient Electrocatalytic Oxygen Reduction

燃料电池阴极氧还原(ORR)催化剂目前主要以商业Pt/C为主,其高成本和稀缺性极大地限制了燃料电池的广泛应用.为了替代Pt/C催化剂,廉价高效的非贵金属催化剂目前受到了广泛的研究和关注.利用氧化石墨烯(GO)为诱导模板,借助表面丰富的含氧官能团,实现了Co基金属有机框架材料(MOF)(ZIF-67)在GO表面的原位生长,构筑了ZIF-67/GO层状复合材料.热解过程中,石墨烯的存在有效抑制了Co纳米颗粒的团聚,并且很好地维持了原始的层状结构.最终获得的Co@N-C/rGO复合催化剂材料实现了活性位的高度分散,并且具有丰富的孔结构和优异的导电性能.在电化学性能测试中Co@N-C/rGO表现出优异的ORR性能,其起始电位为0.96 V,半波电位0.83 V,远优于ZIF-67直接热解得到的Co@N-C材料,且性能与商业Pt/C催化剂相当.此外,Co@N-C/rGO复合催化剂还表现出良好的催化稳定性和甲醇耐受性,显示出该材料作为燃料电池氧还原催化剂的重要潜力.

Commercial Pt/C,with the ideal 4etransfer process for oxygen reduction reaction(ORR),is regarded as the optimal cathode catalyst of fuel cells at present.However,as a noble metal element,the high cost and scarcity of Pt seriously restrict the wide application of fuel cells.On account of this,cheap and high-performance non-noble metal catalysts receive extensive research attentions at present.In this work,by using graphene oxide(GO)as the template,we can realize the in-situ growth of Co-based metal organic framework(MOF)(ZIF-67)on the GO surface by means of the abundant oxygen-containing functional groups on GO,forming the ZIF-67/GO layered composite.During the pyrolysis at 700℃in Natmosphere,the graphene can effectively inhibit the agglomeration of Co nanoparticles with the well retained layered morphology,which can be confirmed by scanning electron microscope(SEM)and transmission electron microscopy(TEM).The X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),Raman spectroscopy and nitrogen isothermal adsorption tests were used to analyze the components and microstructure of obtained materials.Moreover,the catalytic performances of different material towards ORR have been also measured by cyclic voltammetry(CV)and linear sweep voltammetry(LSV)analysis in alkaline electrolyte with rotating disk electrode(RDE)at different speeds.Thanks to the high dispersion of active sites,abundant pore structures and excellent conductivity of the obtained Co@N-C/rGO composite,it shows excellent ORR performances with an initial potential of 0.96 V and a half-wave potential of 0.83 V,far superior to that of the Co@N-C catalyst obtained by direct pyrolysis of ZIF-67,and even comparable to that of commercial Pt/C catalyst.In addition,the Co@N-C/rGO composite also exhibits good catalytic stability under constant potential for 20000 s and shows favorable methanol tolerance which is better than Pt/C,demonstrating its great potential as an oxygen reduction catalyst for fuel cell applications.