The Power of Ions: How They Affect Graphene Supercapacitors

Graphene-based supercapacitors are impressive in storing energy. But understanding how ions interact at the nanoscale with graphene is still puzzling scientists. To solve this, researchers used two types of graphene field-effect transistors (GFETs), one with no substrate (SF-GFETs) and another with an oxide support (OS-GFETs). They wanted to see how ionic concentration and surface potential alter the interface and capacitance. In SF-GFETs, they found that as ion concentration increased, the hysteresis of the Dirac point shifted from positive to negative values. This change also affected the capacitance, reducing it from 4 to 2 F/g. In OS-GFETs, the hysteresis was consistently negative, and the capacitance decreased from 53 to 16 F/g with higher ion concentrations.This shift happens because the neat water structure at the graphene-water interface gets replaced by ion clusters. This transition is key to understanding why capacitance varies. Researchers used the first-order Hill equation to model this relationship, finding specific values ( K = 1. 0131 × 10 -4 for KCl and K = 6. 6237 × 10 -5 for MgCl 2 ) that match the variations in ion hydration. This work is crucial for understanding how nano-arrangements affect the performance of supercapacitors, hinting at potential improvements in their design and performance.