Scalable and controlled creation of nanoholes in graphene by microwave-assisted chemical etching for improved electrochemical properties

Nanoholes on the basal plane of graphene can provide abundant mass transport channels and chemically active sites for enhancing the electrochemical performance. However, current thermal chemical etching processes to manufacture these nanoholes commonly suffer from insufficient process efficiency, scalability and controllability, due to the conventional bulk heating strategy lacks capability to promote the etching reactions. To address this issue, a novel process is developed using microwave irradiation to promote and control the chemical etching of graphene. In this process, the microwave can induce a selective heating of graphene in the liquid solution and then facilitate the etching reactions occurring on the graphene-etchant interface. Applying this strategy, a remarkable reduction of processing time from hour-scale to minute-scale compared to the conventional approaches have been achieved with the control of the population and area percentage of nanoholes on the graphene basal plane. Density functional theory and molecular dynamics simulations revealed that the formation of nanoholes originated from the cyclic etchant oxidation process occurring at the edge-sites atoms around pretreated vacancies on graphene basal plane. The obtained holey graphene oxide sheets exhibit excellent capacitive performance and electrochemical catalytic activity due to the improvements in the accessible surface area, ion diffusion, and heterogeneous charge transfer.