吡啶掺杂碳载钴酞菁催化氧还原的电化学性能及在燃料电池中的应用

Electrochemical Behavior of Pyridine-Doped Carbon-Supported Co-Phthalocyanine (Py-CoPc/C) for Oxygen Reduction Reaction and Its Application to Fuel Cell

以碳黑(VulcanXC-72R)为载体,吡啶(Py)和钴酞菁(CoPc)为催化剂前驱体,经溶剂分散法制备了Py掺杂碳负载纳米钴酞菁复合催化剂(Py-CoPc/C).通过扫描电镜-能谱分析(SEM-EDS)、X射线光电子能谱(XPS)分析和X射线衍射(XRD)分析技术对催化剂的组成和微观结构进行了表征,并运用线性扫描循环伏安法(LSV)和旋转圆盘电极(RDE)技术考察了不同Py掺杂含量对碳载钴酞菁(CoPc/C)催化氧还原反应(ORR)活性的影响及稳定性.结果显示:Py掺杂可以明显改善CoPc/C对ORR的电催化性能,其中掺杂20%Py下所制备的20%Py-20%CoPc/C催化剂对ORR表现出最佳的催化活性,以其制备的气体扩散电极在O2气氛饱和的0.1mol·L-1KOH电解质溶液中,0.2V(相对于标准氢电极)即可产生明显的氧还原电流,半波电位为-0.03V.相比于40%Py/C和未掺杂的40%CoPc/C,20%Py-20%CoPc/C催化剂的半波电位分别正移了160和15mV.进一步运用RDE理论研究表明,在Py-CoPc/C电极上ORR的电子转移总数为2.38,高于CoPc/C电极上的电子转移总数1.96,从而使ORR的选择性明显提高.SEM-EDS和XRD分析表明Py掺杂提高了CoPc/C催化剂的分散性和N含量,更利于O2的吸附.XPS分析表明:吡啶结构的N与石墨结构的N均存在于Py-CoPc/C催化剂中,与催化剂表面的Co离子配位可能是促使ORR活性提高的原因.最后以20%Py-20%CoPc/C制备了膜电极组装(MEA)电极,应用于H2/O2燃料电池单电池发电,室温下获得最大发电功率密度为21mW·cm-2,相对于CoPc/C提高至2.4倍.

Pyridine-doped, carbon-supported Co-phthalocyanine （Py-CoPc/C） nanoparticle catalysts were synthesized via a combined solvent-impregnation and milling procedure, using Co-phthalocyanine （CoPc） and pyridine （Py） as the catalyst precursors. The morphologies and compositions of the catalysts were characterized using X-ray diffraction （XRD）, scanning electron microscopy-energy dispersive X-ray spectroscopy （SEM-EDS）, and X-ray photoelectron spectroscopy （XPS）. The electrocatalytic activities and stabilities were evaluated by linear sweep voltammetry （LSV）, using a rotating disk electrode technique, in terms of their oxygen reduction reaction （ORR） activity as a function of Py doping. The results show that Py doping can significantly improve the catalytic activity of CoPc/C toward the ORR, and the optimal Py doping level is around 20% （i.e., 20%Py-20%CoPc/C）, for which an onset potential of 0,20 V （vs SHE） and a half-wave potential of-0,03 V were achieved in 0.1 mol. L-1 KOH electrolyte. Compared with 40% Py/C and the 40% CoPc/C catalyst, the half-wave potential on the 20% Py-20% CoPc/C catalyst for the ORR shifted positively by 160 mV and 15 mV, respectively. The number of electrons transferred for the ORR also increased from 1.96 to 2.38, indicating an enhancement in ORR selectivity. Scanning electron microscopy-EDX and XRD analysis revealed that the N mass fraction （w） and dispersion of CoPc on carbon are improved by Py doping, which improves adsorption of 02 molecules on the catalyst surfaces. XPS analysis clearly showed pyridinic-N and graphitic-N in the Py-CoPc/C catalysts. Both are believed to be coordinated to Co ions on the catalyst surfaces, and this might be responsible for the enhanced ORR activity. An HJO2 fuel cell using membrance electrode assembly （MEA）, fabricated with a 20%Py-20%CoPc/ C cathode catalyst, generated a peak power density of 21 mW. cm-1, which is 2.4 times that of CoPc/C under the same operating conditions.