Gravity field-mediated synthesis of carbon-conjugated quantum dots with tunable defective density for enhanced triiodide reduction

Integration/alternation of the short- and long-range order carbon species into one is always a trade-off between exposed armchair or zig-zag sites for enhancing the density of local charge states and electronic conductivity for fastening charge transfer. However, the strategies available now for coupling suffer from multiple/complicated steps, which makes the carbon-conjugated microstructure and electronic structure of the carbon as well as the process difficult to be controlled. Herein, surface coupling engineering mediated by external gravity field enables the assembling of carbon quantum dots (CQDs) with short-range periodicity on carbon sphere (CS) with long-range periodicity. The concentration gradient of CQDs on the surface of CS (CQDs/CS-x) can be finely controlled by the tuned gradient field strength, finally achieving the controllable regulation of defective density and electron transfer capability in carbon-conjugated CQDs. The resultant CQDs/CS-4 composite exhibits a high power conversion efficiency up to 8.42% with a low Epp value of 0.11 V, as probed by triiodide reduction. Taken together, density functional theory calculations and experimental results reveal that the edge/defective sites derived from CQDs modulate the charge density of local sites for enhanced capability of the adsorption for I2 molecule, and meanwhile the long-range π-π conjugated configuration of CS sites promotes the fast electron transfer in the carbon-conjugated CQDs. The design concept in this work presents a simple & facile technology for integration of the micro/nano-structured carbon materials with different scales to achieve the delicate regulation. Also, this provides fundamental guidance towards the assembly of ultrafine structure especially small-sized/ultrathin materials at atomic scales.