Modulating the in-plane local charge density of graphene via carbon quantum dots for enhanced triiodide reduction

The intrinsic nature of micro/nano-structured carbon materials is fundamentally relevant to the states of surface charge distribution at the nano-scale level, and the corresponding relationship urgently needs to be modulated and probed. Herein, we modulate the in-plane local charge density on reduced graphene oxide (rGO) by a carbon quantum dot (CQD)-mediated interface-chemistry strategy, realizing charge enrichment over the surface of rGO, which is firstly probed and synchronously visualized with nano-scale topography measurements by electronic mapping. The short-range-ordered CQDs that possess a higher surface potential than the long-range-ordered rGO can act as a charge modulator for efficient and intrinsic electron injection from CQDs to rGO. As a proof-of-concept, the CQDs with a tunable loading are integrated into the surface of rGO by gradient centrifugation. Compared with the basal-plane sites (about 0 nA), the edge sites of rGO and the attached CQDs manifest a strong response of TUNA current, where the responsive current is positively correlated with the density of edge-plane sites and can be modulated up to 160 nA, visualized using PeakForce TUNA. The characteristics of local charge enrichment are also conducive to improving the intrinsic electrocatalytic properties of rGO with pi electron delocalization, proved by using the obtained CQD-coupled rGO materials as an effective electrocatalyst comparable to Pt for the triiodide reduction. This work builds an efficient method for modulating and probing the micro-electron characteristics of advanced carbon materials, further achieving an intuitive and visualized verification regarding the relationship between edge-plane sites and the in-plane surface charge density of the carbon substrate.