Perspectives on electron transfer kinetics across graphene-family nanomaterials and interplay of electronic structure with defects and quantum capacitance.

This perspective presents a combined experimental-theory investigation of the mechanistic outer-sphere electron transfer (OS-ET) kinetics in an adiabatic regime for a cornerstone electrochemical reaction, fundamental to efficient energy interconversion as in electrochemical double layer supercapacitors, across graphene-family nanomaterials (GFNs) ranging from pristine graphene to nitrogen-doped graphene aerogel and the novel laser-induced graphene. Using scanning electrochemical microscopy (SECM) operating in feedback mode and co-located spectroscopy, the ET rate constant, k0 (or kET, cm/s) was quantified while imaging electroactivity of potassium hexacyanoferrate (III/IV) [Fe (CN)64-/3-] or ferrocene methanol [Fc0/Fc+] redox probe yielding unexpected trends. We examined factors affecting the kinetic rate constant, rationalized through a physical model and parameterized using density functional theory by incorporating defects and dopants. We attributed the improved kinetic rates (0.01-0.1 via SECM) compared with ensemble-averaged method (0.001-0.01 cm/s) to point-like topological defects in basal plane (number density ~ 1012/cm2), oxygen functional groups (C/O ratio: 4:1-12:1), nitrogen doping, and edge plane hydrogen-bonding sites (density: 0.1-1.0 μm-1), altering the electronic structure factored into available density of states near Fermi level (- 0.2 to  + 0.2 eV), and quantum capacitance. We elucidated the ET kinetics tunability by engineering the electronic band structure, varying electrode potential, and morphological diversity.