Nitrogen-coordinated single-cobalt-atom electrocatalysts, particularly ones derived from high-temperature pyrolysis of cobalt-based zeolitic imidazolate frameworks (ZIFs), have emerged as a new frontier in the design of oxygen reduction cathodes in polymer electrolyte fuel cells (PEFCs) due to their enhanced durability and smaller Fenton effects related to the degradation of membranes and ionomers compared with emphasized iron-based electrocatalysts. However, pyrolysis techniques lead to obscure active-site configurations, undesirably defined porosity and morphology, and fewer exposed active sites. Herein, a highly stable cross-linked nanofiber electrode is directly prepared by electrospinning using a liquid processability cobalt-based covalent organic polymer (Co-COP) obtained via pyrolysis-free strategy. The resultant fibers can be facilely organized into a free-standing large-area film with a uniform hierarchical porous texture and a full dispersion of atomic Co active sites on the catalyst surface. Focused ion beam-field emission scanning electron microscopy and computational fluid dynamics experiments confirm that the relative diffusion coefficient is enhanced by 3.5 times, which can provide an efficient route both for reactants to enter the active sites, and drain away the produced water efficiently. Resultingly, the peak power density of the integrated Co-COP nanofiber electrode is remarkably enhanced by 1.72 times along with significantly higher durability compared with conventional spraying methods. Notably, this nanofabrication technique also maintains excellent scalability and uniformity.
Keywords: acidic oxygen reduction reaction; cross-linked nanofiber electrodes; porous covalent organic polymers; proton exchange membrane fuel cells.
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