Microwave-assisted synthesis of ZIF-9@xGO composites as cooperative electrocatalysts for electro-oxidation of benzyl alcohols coupled with H2 production

Abstract

Selective electrochemical oxidation of alcohols to their corresponding aldehydes or acids utilizing water as the oxygen source is not only considered a green and sustainable approach to synthesize value added chemicals but also economically demanding as the overall process is coupled with green H₂ production. However, restricted production due to low current density and the use of expensive noble-metal-based electrocatalysts has limited its industrial viability. On the other hand microwave-assisted synthesis enables a rapid, economical and effective way to fabricate various advanced porous materials. In this regard, herein we report microwave assisted rapid synthesis of a metal–organic framework materials ZIF-9 nanocrystals and ZIF-9@xGO composites by varying the wt% of graphene oxide (GO). Remarkably, upon GO loading the current density increases significantly from 75 mA cm⁻² to 204 mA cm⁻² at 1.6 V vs. RHE in an alkaline solution with 0.1 M benzyl alcohol, thereby imparting direct impact towards benzoic acid yield (∼84%) and faradaic efficiency (∼88%) of the process. Moreover, the optimised electrocatalyst (i.e. ZIF-9@10GO) exhibits a H₂ evolution rate of 273 mmol g⁻¹ h⁻¹ in the presence of benzyl alcohol. Our results indicate that in situ generated Co(OH)₂/CoOOH hybrid species over the ZIF-9 surface plays an active role in this electrocatalysis. Additionally, this electrocatalytic system shows good functional group tolerance, exhibiting wide scope for different substrates with high faradaic efficiency.