A hydrogen evolution reaction induced unprecedentedly rapid electrocatalytic reduction of 4-nitrophenol over ZIF-67 compare to ZIF-8

ZIF-8 is built with Zn2+ tetrahedrally bridging with imidazole units, whereas ZIF-67 has the similar structure with Co2+ replacing the Zn ions. ZIF-8 and ZIF-67 were synthesized by a single step at room temperature, and the detailed characterization through XRD and FE-SEM study revealed similar surface morphology of the two isostructural ZIFs. Again, the chemical and thermal stability studies exhibited the better stability of ZIF-8 over ZIF-67. The through characterizations also revealed the better surface area and porosity and adsorption of 4-nitrophenol over ZIF-8 compare to ZIF-67. Interesting, in spite of inferior physical properties, ZIF-67 revealed better electrocatalytic properties between the isostructural ZIFs. ZIF-67 showed unprecedentedly fast reduction of 4nitrophenol to 4-aminophenol, whereas the reduction of 4-nitrophenol over ZIF-8 took almost 180 min, in-spite of better adsorption. The detailed mechanistic studies revealed that the electrocatalytic reduction of 4-nitrophenol over ZIF-8 electrode underwent through an orthodox 6e(-) system pathway to produce 4-aminophenol through hydroxyl amine and nitroso containing intermediates. Whereas, ZIF-67 produced hydrogen through water splitting that directly reduced 4-nitrophenol to 4-aminophenol with complete product selectivity.