Zhu Weikang, Pei Yabiao, Liu Yang, Zhang Junfeng, Qin Yanzhou, Yin Yan, Guiver Michael D
State Key Laboratory of Engines, School of Mechanical Engineering, Tianjin University, Tianjin 300072, People's Republic of China.
ACS Appl Mater Interfaces. 2020 Jul 22;12(29):32842-32850. doi: 10.1021/acsami.0c08829. Epub 2020 Jul 9.
Developing highly efficient non-noble metal catalysts for the cathode of fuel cells is an urgent requirement for reducing the cost. Although the intrinsic activity of non-noble metal materials has been greatly improved, the fuel cell performance is also determined by the mass transfer within the catalyst layer (CL), particularly at high current density. Electrochemical impedance spectroscopy (EIS) combined with rotating disk electrode (RDE) analysis is a powerful tool to quantitatively analyze the influence of the structural properties on CL performance. Here, Co/N/C CLs with gradient pore structures are constructed based on the controllable synthesis of zeolitic imidazolate framework (ZIF)-derived catalyst. The influences of the carbon support, active site, and catalyst loading are comprehensively studied by EIS in different regions (kinetic and mixed-diffusion). The results indicate that a high micro-/mesopore ratio is beneficial to increasing the density of active sites while reducing the mass-transfer efficiency. Inversely, abundant mesopores promote mass transfer, but they result in low active site density. By carefully adjusting the pore structure and chemical composition of the ZIF-derived catalyst, the Co/N/C CL shows a low mass-transfer resistance (95.5 Ω at 0.75 V vs RHE). This work demonstrates the importance of mass transfer within the fuel cell CL, beyond seeking only high activity.
开发用于燃料电池阴极的高效非贵金属催化剂是降低成本的迫切需求。尽管非贵金属材料的本征活性已得到极大提高，但燃料电池性能还取决于催化剂层（CL）内的传质，尤其是在高电流密度下。电化学阻抗谱（EIS）与旋转圆盘电极（RDE）分析相结合是定量分析结构特性对CL性能影响的有力工具。在此，基于可控合成沸石咪唑酯骨架（ZIF）衍生催化剂构建了具有梯度孔结构的Co/N/C CL。通过EIS在不同区域（动力学和混合扩散）全面研究了碳载体、活性位点和催化剂负载量的影响。结果表明，高微孔/介孔比有利于增加活性位点密度，同时降低传质效率。相反，丰富的介孔促进传质，但会导致活性位点密度低。通过仔细调整ZIF衍生催化剂的孔结构和化学成分，Co/N/C CL表现出低传质电阻（在0.75 V相对于可逆氢电极时为95.5 Ω）。这项工作证明了燃料电池CL内传质的重要性，而不仅仅是追求高活性。
