The CO poisoning effect on carbon-supported platinum catalysts ͑at a loading of 0.5 mg Pt/cm 2 per electrode͒ in polymer electrolyte membrane fuel cells ͑PEMFCs͒ has been investigated in a temperature range from 125 to 200°C with the phosphoric acid-doped polybenzimidazole membranes as electrolyte. The effect is very temperature-dependent and can be sufficiently suppressed at elevated temperature. By defining the CO tolerance as a voltage loss less than 10 mV, it is evaluated that 3% CO in hydrogen can be tolerated at current densities up to 0.8 A/cm 2 at 200°C, while at 125°C 0.1% CO in hydrogen can be tolerated at current densities lower than 0.3 A/cm 2 . For comparison, the tolerance is only 0.0025% CO ͑25 ppm͒ at 80°C at current densities up to 0.2 A/cm 2 . The relative anode activity for hydrogen oxidation was calculated as a function of the CO concentration and temperature. The effect of CO 2 in hydrogen was also studied. At 175°C, 25% CO 2 in the fuel stream showed only the dilution effect.

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Metal,N-codoped carbon (M-N-C) nanostructures are promising electrocatalysts toward oxygen reduction reaction (ORR) or other gas-involved energy electrocatalysis. Further creating pores into M-N-C nanostructures can increase their surface area, fully expose the active sites, and improve mass transfer and electrocatalytic efficiency. Nonetheless, it remains a challenge to fabricate M-N-C nanomaterials with both well-defined morphology and hierarchical porous structures. Herein, high-quality 2D Cu-N-C nanodisks (NDs) with biomimic stomata-like interconnected hierarchical porous topology are synthesized via carbonization of Cu-tetrapyridylporphyrin (TPyP)-metal-organic frameworks (MOFs) precursors and followed by etching the carbonization product (Cu@Cu-N-C) along with re-annealing treatment. Such hierarchical porous Cu-N-C NDs possess high specific surface area (293 m 2 g −1 ) and more exposed Cu single-atom sites, different from their counterparts (Cu@Cu-N-C) and pure N-C control catalysts. Electrochemical tests in alkaline media reveal that they can efficiently catalyze ORR with a half-wave potential of 0.85 V (vs reversible hydrogen electrode), comparable to Pt/C and outperforming Cu@Cu-N-C, N-C, Cu-TPyP-MOFs, and most other reported M-N-C catalysts. Moreover, their stability and methanol-tolerant capability exceed Pt/C. This work may shed some light on optimizing 2D M-N-C nanostructures through bio-inspired pore structure engineering, and accelerate their applications in fuel cells, artificial photosynthesis, or other advanced technological fields. Scheme 1. Schematic diagram for the synthetic process of Cu-N-C-ICHP NDs and the stomata structure of plant leaves. 1902410 (3 of 11) www.advancedsciencenews.com

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