Electrospun Iridium-Based\nNanofiber Catalysts for\nOxygen Evolution Reaction: Influence of Calcination on Activity–Stability\nRelation

The enhanced utilization of noble metal catalysts through\nhighly\nporous nanostructures is crucial to advancing the commercialization\nprospects of proton exchange membrane water electrolysis (PEMWE).\nIn this study, hierarchically structured IrO<sub><i>x</i></sub>-based nanofiber catalyst materials for acidic water electrolysis\nare synthesized by electrospinning, a process known for its scalability\nand ease of operation. A calcination study at various temperatures\nfrom 400 to 800 °C is employed to find the best candidates for\nboth electrocatalytic activity and stability. Morphology, structure,\nphase, and chemical composition are investigated using a scale-bridging\napproach by SEM, TEM, XRD, and XPS to shed light on the structure–function\nrelationship of the thermally prepared nanofibers. Activity and stability\nare monitored by a scanning flow cell (SFC) coupled with an inductively\ncoupled plasma mass spectrometer (ICP-MS). We evaluate the dissolution\nof all metals potentially incorporated into the final catalyst material\nthroughout the synthesis pathway. Despite the opposite trend of performance\nand stability, the present study demonstrates that an optimum between\nthese two aspects can be achieved at 600 °C, exhibiting values\nthat are 1.4 and 2.4 times higher than those of the commercial reference\nmaterial, respectively. The dissolution of metal contaminations such\nas Ni, Fe, and Cr remains minimal, exhibiting no correlation with\nthe steps of the electrochemical protocol applied, thus exerting a\nnegligible influence on the stability of the nanofibrous catalyst\nmaterials. This work demonstrates the scalability of electrospinning\nto produce nanofibers with enhanced catalyst utilization and their\ntesting by SFC-ICP-MS. Moreover, it illustrates the influence of calcination\ntemperature on the structure and chemical composition of the nanofibers,\nresulting in outstanding electrocatalytic performance and stability\ncompared to commercial catalyst materials for PEMWE.