Water-Phase Lateral Interconnecting Quantum Dots as Free-Floating 2D Film Assembled by Hydrogen-Bonding Interactions to Acquire Excellent Electrocatalytic Activity

Supramolecular self-assembly of nanoparticles in two orthogonal directions would potentially allow one to fabricate nanomaterials with fascinating properties. In this study of a hydrothermal polycondensation of melamine/cyanuric acid, graphitic carbon nitride-based quantum dots (CNQD, ∼2 nm) are in situ arranged along two orthogonal directions through lateral hydrogen bonding, and free-floating two-dimensional hydrogen-bonded films of CNQD (2D CNQD) are built. On the basis of the universality of this hydrothermal in situ supramolecular self-assembly technique, 2D films linked by other quantum dots such as sulfur-doped graphitic carbon nitride and CdTe are also constructed. With the benefits of stimuli responsiveness and the reversibility of hydrogen bonds, controllable assembly/disassembly of the 2D CNQD film is feasibly achieved by external stimuli such as inletting CO2/N2, which endows the assembled 2D CNQD films optimal electrochemical superiorities of both 2D film and zero-dimensional (0D) quantum dots. Accordingly, the 2D CNQD film delivers a high bifunctional activity in both a nitrogen reduction reaction (NRR) and an oxygen evolution reaction (OER). Especially in NRR, it exhibits the high yield rate of NH3 reaching 75.07 μg h–1 mg–1 at −0.85 V versus reversible hydrogen electrode at ambient condition. Strikingly, the power density of the rechargeable Zn–N2 battery using 2D CNQD film as cathode reaches 31.94 mW cm–2, outperforming the majority of Zn–N2 batteries. Density functional theory calculations proved the promoted adsorption of N2 and stabilized NRR intermediates on 2D CNQD cooperated by multiply hydrogen-bonding interactions are the main reasons for the excellent NRR electrocatalytic performances. This work hints that hydrothermal in situ supramolecular self-assembly is a feasible and direct way to integrate 0D quantum dots into 2D directional arrays, and the hydrogen bond that interlinks enables this free-floating 2D structure to maintain the electrochemical superiority of both 0D and 2D structures.