Synthesis of a conjugated porous Co(II) porphyrinylene-ethynylene framework through alkyne metathesis and its catalytic activity study

The development of efficient catalysts for the oxygen reduction reaction (ORR) is crucial for a number of emerging technologies, to counter energy and environment crises. Herein, we report an alkyne metathesis polymerization protocol to synthesize a conjugated microporous metalloporphyrin-based framework containing interconnected ORR catalytic centers. A simple composite of the framework and carbon black shows excellent ORR electrocatalytic activity and specificity through a four-electron reduction mechanism under both acidic and alkaline conditions. The pyrolysis of the catalyst, which is commonly involved in the preparation of ORR catalytic systems, is not necessary. Compared to monomeric metalloporphyrins, the framework shows enhanced ORR catalytic activity, presumably due to the porous and conjugated nature of the framework structure, which allows better exposure of the catalytically active sites, and efficient electron/mass transport. More importantly, the composite electrocatalyst exhibits superior durability and methanol tolerance over commercial Pt/C and metalloporphyrin monomers. Given the highly structural tunability of conjugated microporous polymers, it is conceivable that such a non-pyrolytic approach could enable the systematic exploration of the structure-activity relationship of organic framework-based ORR catalysts and eventually lead to the development of cost-effective replacements for Pt/C.