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The natural abundance, biodegradability, and low density of plant 昀椀bers, together with biobased epoxy thermoset resin, have driven the increasing popularity of plant 昀椀ber/polymer composites (PFRPs) to wider applications in various industries. However, the striving for biomass-based 昀氀ame retardants (FRs) treatment for PFRPs remained a bottleneck due to polymers’ inherent vulnerability against 昀椀re and the increasing environmental awareness. In this work, a facile two-step aqueous solution coating process was proposed for fabric surface treatment of 昀氀ax fabric using fully biobased phytic acid and chitosan from polysaccharides. The treated 昀氀ax fabric demonstrated self-extinguishing behavior when ignited and showed a decrease in peak heat release rate (PHRR) by 58% under combustion. The laminate produced by this treated 昀氀ax fabric and biobased epoxy resin showed a decrease of PHRR by 36% and an increase of more than 200% for the time of torch 昀椀re burn-through, demonstrating intriguing 昀氀ame retardance brought by only FRs treatment on 昀氀ax fabric reinforcements. Various measurements were done to elaborate on the role of treated 昀氀ax fabric in the 昀氀ame retardancy of polymer composites. 

One of the key challenges that hinders broad commercialization of proton exchange membrane fuel cells is the high cost and inadequate performance of the catalysts for the oxygen reduction reaction (ORR). Here we report a composite ORR catalyst consisting of ordered intermetallic Pt-alloy nanoparticles attached to an N-doped carbon substrate with atomically dispersed Fe–N–C sites, demonstrating substantially enhanced catalytic activity and durability, achieving a half-wave potential of 0.923 V ( vs.  RHE) and negligible activity loss after 5000 cycles of an accelerated durability test. The composite catalyst is prepared by deposition of Pt nanoparticles on an N-doped carbon substrate with atomically dispersed Fe–N–C sites derived from a metal–organic framework and subsequent thermal treatment. The latter results in the formation of core–shell structured Pt-alloy nanoparticles with ordered intermetallic Pt 3 M (M = Fe and Zn) as the core and Pt atoms on the shell surface, which is beneficial to both the ORR activity and stability. The presence of Fe in the porous Fe–N–C substrate not only provides more active sites for the ORR but also effectively enhances the durability of the composite catalyst. The observed enhancement in performance is attributed mainly to the unique structure of the composite catalyst, as confirmed by experimental measurements and computational analyses. Furthermore, a fuel cell constructed using the as-developed ORR catalyst demonstrates a peak power density of 1.31 W cm −2 . The strategy developed in this work is applicable to the development of composite catalysts for other electrocatalytic reactions. 

Abstract Fe‐N‐C single‐atom catalysts (SACs) are emerging as a promising class of electrocatalysts for the oxygen reduction reaction (ORR) to replace Pt‐based catalysts. However, due to the limited loading of Fe for SACs and the inaccessibility of internal active sites, only a small portion of the sites near the external surface are able to contribute to the ORR activity. Here, this work reports a metal–organic framework‐derived Fe‐N‐C SAC with a hierarchically porous and concave nanoarchitecture prepared through a facile but effective strategy, which exhibits superior electrocatalytic ORR activity with a half‐wave potential of 0.926 V (vs RHE) in alkaline media and 0.8 V (vs RHE) in acidic media while maintaining excellent stability. The superior ORR activity of the as‐designed catalyst stems from the unique architecture, where the hierarchically porous architecture contains micropores as Fe SAC anchoring sites, meso‐/macro‐pores as accessible channels, and concave shell for increasing external surface area. The unique architecture has dramatically enhanced the utilization of previously blocked internal active sites, as confirmed by a high turnover frequency of 3.37 s⁻¹and operando X‐ray absorption spectroscopy analysis with a distinct shift of adsorption edge.