Carbon nanomaterials (CNMs, carbon dots, carbon nanotubes, and graphene) have received much attention in recent decades for their technological roles as electrocatalysts for biosensing and fuel cell applications in aqueous solutions. Their complex form factor presents challenges for delineating structure–property relationships, namely the interplay of electroactive area surface defects and exposed graphene planar structure, for optimizing their electrocatalytic activity. Conflicting examples in the literature show higher defect density in the graphene structure with increased or decreased conduction of the material. The graphenyl sheet curvature, voltage range of the electrochemical redox reaction, dispersion of charged impurities affecting the charge mobility, and overall resistivity of the CNM materials should be considered to optimize the overall electrochemical activity, particularly as they relate to redox reactions taking place in the −0.2 to +0.3 V standard potential range.