Supercapacitive performance of electrodes based on defective ZnO nanorods anchored on graphene nanowalls

Abstract

Vertical graphene nanowalls (GNWs) have emerged as a highly promising architectural structure, offering a vast surface area teeming with active sites and expediting ion diffusion. In our relentless pursuit of bolstering their specific capacitance, we unveil a groundbreaking supercapacitive augmentation, incorporating defect-engineered ZnO nanorods (ZNRs) branching out from the GNWs. The realization of this hierarchical structure is achieved through a meticulous multi-step process, featuring inductively coupled plasma-chemical vapor deposition, magnetron sputtering, and hydrothermal synthesis. The presence of oxygen vacancy (OV) defects within the ZNRs, induced by argon annealing, has been characterized using X-ray photoelectron spectroscopy (XPS). The emergence of OV defects below the conduction band of the ZNRs results in a narrowing of the bandgap within the hybrid structure, thereby enhancing its conductivity and increasing the reaction sites. The capacity of the ZNRs/GNWs hybrid electrodes were evaluated in an aqueous KOH electrolyte solution, operating within a voltage range of 0.5 V and at a current density of 0.1 mA cm−2. This assessment yielded an area capacitance of 21.45 mF cm−2, signifying a 1.5-fold increase in capacitance compared to GNWs grown on graphite sheets. The ZNRs/GNWs hybrid demonstrates remarkable electrochemical performance and exhibits substantial potential for energy storage applications. Our work is expected to offer valuable insights for the enhancement of electrochemical properties in various composite and hybrid materials.