Iron-Cluster-Directed Synthesis of 2D/2D Fe-N-C/MXene Superlattice-like Heterostructure with Enhanced Oxygen Reduction Electrocatalysis.

Metal clusters, an emerging category of materials with molecular metal dispersity, have been proposed for versatile applications. In this work, we show an unexpected function of metal clusters, which can contribute to preparing 2D/2D superlattice-like heterostructures. The key step is to use metal clusters to adjust the surface charge of 2D nanosheets and, consequently, match the charge negativities per surface area for different 2D nanosheets, which facilitate the electrical-driven assembly of these nanosheets into a superlattice-like heterostructure in aqueous solutions. Accordingly, iron-cluster-directed cationic Fe-N-C nanosheets (Zeta potential: +30.4 mV) have been assembled with anionic MXene (Zeta potential: -39.7 mV) to produce a superlattice-like heterostructure characteristic of a lateral size of around tens of nanometers, a surface area of 30 m2 g-1, and ultrathickness of several nanometers with repeated dimensions of 0.4 and 2.1 nm. Potential application of the synthesized Fe-N-C/MXene heterostructure has been demonstrated for electrocatalytic oxygen reduction reaction (ORR) that shows a positive onset potential of 0.92 V, four-electron transfer pathway, and strong durability of 20 h in alkaline electrolyte. This work suggests that metal clusters can assist the assembly of low-dimensional architectures for energy-related applications.