Self-assembled ZIF-67@graphene oxide as a cobalt-based catalyst precursor with enhanced catalytic activity toward methanolysis of sodium borohydride

Abstract

In this work, a composite consisting of ZIF-67 and graphene oxide (GO) was successfully synthesized by a facile in-situ synthesis method and applied in hydrogen release from the methanolysis of sodium borohydride (NaBH4). Physicochemical properties of pure ZIF-67 and the ZIF-67@GO composites are well characterized by XRD, BET, SEM and HRTEM. It was observed that the ZIF-67 crystals are intimately anchored on GO sheets. An increase of GO in the composite led to a marked decrease of the BET surface area and an increased average pore size. However, the ZIF-67@GO precursor with high GO doping exhibited much higher activity toward the methanolysis of NaBH4, which suggests that the good conductivity of GO is beneficial to improve the catalytic performance. The ZIF-67@GO precursor experienced a structure reconstruction during the methanolysis reaction due to the presence of reducible Co2+. Moreover, the reduced ZIF-67@GO displayed a slightly higher activity as compared to the pristine composite and retained excellent durability after five cycles. A possible mechanism for the hydrogen generation from the methanolysis of NaBH4 using a ZIF-67@GO catalyst was proposed.