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

Abstract

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 CO 2 /N 2 , 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 NH 3 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−N 2 battery using 2D CNQD film as cathode reaches 31.94 mW cm −2 , outperforming the majority of Zn−N 2 batteries. Density functional theory calculations proved the promoted adsorption of N 2 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.

Fe‐Alloyed MoNi Nanohybrids as Oxygen Evolution Reaction/Oxygen Reduction Reaction Bifunctional Electrocatalyst for Rechargeable Zinc–Air Batteries

“…The arc observed in the high‐frequency region of the curve stands for the Faradaic charge transfer resistance of the electrode. [ 42 ] The angle between the curve in the intermediate frequency region and the real axis is the characteristic of ions diffusion to the electrode. [ 43 ] Therefore, according to the semicircle diameter (MoNiFe < MoNi) in the high frequency region of Figure 5d, the electrochemical resistance of MoNiFe nanohybrids is smaller than that of MoNi, due to the enhancement of the electrical conductivity [ 44 ] resulted from the further alloying of Fe element in the MoNi catalyst.…”

Semiconducting Quantum Dots for Energy Conversion and Storage

“…Wang et al. [ 26 ] built a 2D hydrogen‐bonded film of g‐C 3 N 4 ‐based QDs (≈2 nm) via a hydrothermal polycondensation method (Figure 10h). Controllable disassembly/assembly of the 2D g‐C 3 N 4 QD film can be achieved by filling CO 2 /N 2 .…”

“…The development of electrocatalyst with earth-abundant elements for the highly efficient OER is promising, but remains a big challenge. Wang et al [26] built a 2D hydrogen-bonded film of g-C 3 N 4 -based QDs (≈2 nm) via a hydrothermal polycondensation method (Figure 10h). Controllable disassembly/assembly of the 2D g-C 3 N 4 QD film can be achieved by filling CO 2 /N 2 .…”

“…i) The Tafel slopes for 2D g-C 3 N 4 QD film and 0D QDs in 0.1 mol L −1 NaOH electrolyte. Reproduced with permission [26]. Copyright 2022, American Chemical Society.…”

“…[20,21] In fact, quantum dot size modification strategy is used in different types of materials, e.g., metal oxides, [22] metal chalcogenides, [23] metal halides, [24] oxysalts, [25] and nonmetal semiconductors. [26] QD size materials own several unique characteristics, which are promising for the researches in energy conversion and storage. [27,28] On the one hand, QDs have demonstrated unique properties in light harvesting [29,30] and multiple exciton generation (MEG) [31] due to the quantum…”