Ligand-assisted interfacial monomicelle assembly to incorporate intermetallic nanoparticles into mesoporous carbon nanostructures.

Abstract

Intermetallic nanoparticles (iNPs) exhibit ordered superlattice structures characterized by unique properties, for example, long-range ordering, robust metallic bonding and site-isolation effects. Multicomponent (>2) iNPs are particularly interesting for the development of advanced metallic catalysts for electrochemical applications. Integration of iNPs within mesoporous carbon nanostructures enhances mass and electron transfer during electrolysis and provides a protective mesoporous confinement that prevents iNP sintering and loss during operation. Here we describe a generalized two-step strategy to integrate iNPs with up to eight metal components into mesoporous carbon nanostructures that allows control over the ordering degree, phases and morphology. Ligand-assisted interfacial assembly of monomicelles on diverse metal substrates (using a laboratory-made amphiphilic copolymer as a structure-directing agent, with dopamine acting as both carbon precursor and metal-coordinating ligand) results in mesostructured metal-organic superstructures. All of the examples described have at least one noble metal (Pt or Pd) combined with transition metal elements (for example, Fe, Co, among others). Thermal processing of these metal-organic superstructures in an ammonia (NH₃) atmosphere induces the formation of chemically ordered iNPs while simultaneously creating the mesoporous structure. The Protocol also includes procedures for two example electrochemical applications: the oxygen reduction reaction and nitrate reduction reaction for NH₃ production. The entire synthetic procedure takes ~5 d, while physical characterization via electron microscopy, X-ray diffraction and nitrogen sorption isotherms require ~2 d. Investigating the catalytic mechanisms, utilizing in situ Fourier-transform infrared spectroscopy and online differential electrochemical mass analysis typically take 4-6 h for electrocatalytic reactions.