Porous Covalent Organic Polymer Coordinated Single Co Site Nanofibers for Efficient Oxygen‐Reduction Cathodes in Polymer Electrolyte Fuel Cells

Abstract

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.

Flash Nitrogen‐Doped Carbon Nanotubes for Energy Storage and Conversion

“…When the current density was recovered from 200 to 2 mA cm −2 , the voltage platform was almost restored, proving that the battery has outstanding rate performance. [54] Figure S21, Supporting…”

Pyrolysis-Free Covalent Organic Polymers Directly for Oxygen Electrocatalysis

“…We electrospined the ink containing pyrolysis-free Co-COP catalyst and polymer (poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA)) and obtained nanofiber membranes rich in homogeneous CoN 4 active sites (Figure 6c). 4 Practically, the newly developed nanofabrication technique possesses good scalability and consistency after scale-up. Benefiting from the good liquid processability characteristics of COP, the as-obtained 200 cm 2 COP film maintained good consistency at random positions of the film, which is beneficial to future pyrolysis-free oxygenelectrode commercialization.…”

“…10.1002/adma.2022086612023352208661 . Hierarchical pore structures fabricated by electrospinning technology to persistently drive PEMFCs.…”

“…We adjust the electron cloud distribution and the energy-level location of the frontier molecular orbitals in the COP skeleton, allowing the resulting COP-N and COP-B assembling with donor–acceptor units to be simultaneously intercalated and exfoliated in Lewis acids and bases. Under the guidance of these adjustment strategies, we have directly successfully processed and fabricated into free-standing COP oxygen electrodes applied to ZABs and PEMFCs devices from COP solution …”

General synthesis of carbon-guarded cobalt-based nanospheres for oxygen reduction electrocatalysis

“…This improvement can be attributed to the stable nature and enhanced mass/electron transmission of Ni/Co@NC NPs. [40][41][42][43] In a ZAB operated at relatively large current density, the catalytically active components such as the metal-based nanoparticles, tend to fall off the support and aggregate into large-sized chunks due to the weak interaction between the metal and support, which decreases the specific surface area of the catalyst, an issue which decreases the activity of Pt/C. In contrast, the interconnected carbon-guarded Ni/Co alloyed nanoparticles possess strong resistance to aggregation due to the protection of graphitized carbon.…”