摘要
随着材料科学的不断发展,基于过渡金属电催化剂的活性不断提高.与Pt相比,由于其具有成本低、原料来源广等特点,非贵金属催化剂成为近年来燃料电池领域研究的热点.然而,非贵金属的催化层结构、催化性能、传质等方面研究较少,阻碍了过渡金属催化剂(如Co基材料)的进一步发展和燃料电池的应用.目前对非贵金属催化剂的研究主要集中在催化剂的合成和电催化活性研究等方面,对电极结构的设计、传质及氧还原性能影响的机理还不是十分清楚.本研究通过电沉积方法在气体扩散层上原位生长CoS/CoO纳米片催化层,调控沉积条件及后处理方法,合成了不同形貌和化学组成的催化层.通过电化学测试及物化结构分析,探究了气体扩散电极微观结构对氧还原反应(ORR)性能的影响.结果表明,在氩氢混合气(10%氢气+90%氩气)的保护下进行高温煅烧,可以有效避免Co纳米颗粒的团聚并获得较好的ORR活性.
Because of the high cost and scarcity of Pt,the commercialization of fuel cell technology is still facing a great challenge.Compared with the proton exchange membrane fuel cell,one advantage of the anion exchange membrane fuel cell(AEMFC)is the possibility of partially replacing or completely removing Pt catalyst in the cathode.Recently,the oxygen reduction reaction(ORR)of transition metals(such as Fe,Co,Ni as well as their compounds)in alkaline environments has been greatly improved,with substantial efforts devoted to controlling the nanostructure and adjusting the active sites(including the density and chemical structure).Based on rotating disk electrode(RDE)tests,these transition metal compounds show attractive ORR performance as compared with state-of-art Pt/C catalysts.However,when fabricated into films for membrane electrode assembly,these highly active transition metal compounds(such as Co-based materials)do not show satisfactory fuel cell performance,hindering their further development for application in fuel cells.This is because of an insufficient understanding of structure-activity relationships of transition metal catalyst layers for fuel cells.Compared with conventional powder catalysts,nanostructured catalysts directly grown onto a conductive substrate,for example by electrodeposition,are anticipated to construct an electron conductive framework,optimizing the triple-phaseboundary within the catalyst layer.Furthermore,catalyst structures and their arrays can be easily and quickly obtained by the electrodeposition method.In this work,a catalyst layer composed of CoS/CoO nanosheets was grown in situ on a gas diffusion layer by electrodeposition.The morphology and elemental composition of the gas diffusion electrode were analyzed by scanning electron microscope(SEM),energy dispersive spectrometer(EDS)and X-ray diffraction(XRD).The ORR performance of the gas diffusion electrode was evaluated by half-cell,which can better reflect the actual fuel cell working condition compared with RDE analysis.The electrodeposition conditions(deposition cycles,dissolved oxygen)were studied to investigate their influence on the CoS/CoO nanosheets.The results show that the loading of the catalyst on the gas diffusion layer increases with the number of deposition cycles,thus resulting in a higher ORR activity.A gas diffusion electrode prepared in nitrogen atmosphere presents dense nanospheres with less mesoporous structure,showing lower electrochemical active area and poor ORR activity.By contrast,CFP@CoS50 presents nanospheres which consist of nanosheets.To further improve the performance of gas diffusion in the electrode,a post-heat treatment was conducted on CFP@Co S50 under different protective atmospheres and activation temperatures.The results indicate that with the increase of activation temperature under argon atmosphere,the morphology of the nanosheets gradually disappears,and the Co element aggregates to form>1μm particles.However,under the argon-hydrogen mixture(90%argon and 10%hydrogen),the agglomeration of the Co-based nanosheet can be effectively avoided,thus obtaining promising ORR performance.The results show that the CFP@Co S50-500-H;electrode has a predominantly four-electron ORR pathway for direct OH–formation.This work provides a facile electrodeposition method for preparing a transition metal-based electrode with controlled nanostructure,which may open a new avenue for the design of membrane electrode assemblies for next generation fuel cells.
作者
张俊锋
李新天
赵浩阳
裴亚彪
祝伟康
尹燕
Junfeng Zhang;Xintian Li;Haoyang Zhao;Yabiao Pei;Weikang Zhu;Yan Yin(State Key Laboratory of Engines,Tianjin University,Tianjin 300350,China)
出处
《科学通报》
EI
CAS
CSCD
北大核心
2021年第35期4592-4598,共7页
Chinese Science Bulletin
基金
国家自然科学基金(21875161)资助。
关键词
气体扩散电极
电化学沉积
钴基催化剂
氧还原反应
gas diffusion electrode
electrodeposition
cobalt-based catalyst
oxygen reduction reaction
作者简介
联系人:尹燕,E-mail:yanyin@tju.edu.cn。
