NSERC-DFG SUSTAIN: Hierarchically structured cathode catalyst layers prepared by spinodal decomposition for PEM Fuel Cells - From fundamental understanding to application at operation conditions

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Proton exchange membrane fuel cells (PEMFCs) for harnessing electrical energy from hydrogen are considered a key technology in the energy transition. In this international project we tackle the current challenges of an inefficient cathode catalyst layer (CL) in PEMFCs by developing a tailored hierarchical structure for improved catalyst accessibility and mass transport. The optimal architecture of the CL with distinctive channels for proton supply, oxygen and water transport will be realized by spinodal decomposition. This method, in which a homogeneous mixture of two or more components undergoes a triggered phase separation, allows the preparation of hierarchically structured materials, arrested in far-from-equilibrium networks. However, spinodal decomposition has not yet been applied to design highly efficient CLs for PEMFCs. Preliminary results from our consortium verified the feasibility of the concept and resulted in very promising initial results of PEMFCs with enhanced performance. Varying the nature of the demixing fluids, catalyst particles and ionomer architecture in combination with processing conditions allows for multiple factors to control the final hierarchical structure. Conductive atomic force microscopy (c-AFM) will be employed to visualize proton conductive channels in the structure and relate them to localized highly electrochemically active regions, as investigated by combined AFM - Scanning Electrochemical Microscopy (SECM) with high spatial resolution. Finally, the overall accessible Pt electrochemical active surface area (ECSA) and the oxygen transport resistance inside the CL are characterized on the device-level. At the same time, the overall performance of the new CLs is benchmarked to conventional state-of-the-art CLs. Within this project we aim to bridge the gap between structure, microscopic behavior like local electrocatalytic activity and ionomer-catalyst interaction, and improved device performance. The key improvement factors for O2 transport and Pt accessibility are investigated on the micro- and macroscale by microrheology, AFM and electrochemical methods. The gained link will be used to optimize the hierarchical structure based on spinodal decomposition. By combination of the properties determined on the micro- and macroscale and the device-level performance, we aim to establish a link between the microscopic behavior and its macroscopic consequence. Based on this structure-function relationship, we will optimize the hierarchically structured cathode catalyst layers to obtain a superior Pt utilization and improved mass transport. In our interdisciplinary project we combine sophisticated preparation with advanced characterization and device-level electrochemistry to develop a complex, still cost-effective and easy to industrialize, new CL for enhanced PEMFC performance.