Prussian Blue Iron–Cobalt Mesocrystals as a Template for the Growth of Fe/Co Carbide (Cementite) and Fe/Co Nanocrystals

Abstract

Controlling the composition, size, and morphology of transition-metal carbides and metals is important for product selectivity in industrial catalytic processes, such as in the Fischer–Tropsch synthesis (FTS). The formation of iron–cobalt carbide nanocatalysts can enhance selectivity in the FTS process if the iron to cobalt ratios are controlled. Unfortunately, this is difficult to achieve in nanocrystals due to ion migration, differences in formation rates, and the requirement of perfect critical nuclei to form prior to the growth of the nanocrystal in colloidal synthesis. In this manuscript, a mixed metal iron–cobalt Prussian blue analogue (PBA) mesocrystal is shown to act as a template for isolating pure phase iron–cobalt carbide and iron–cobalt alloy nanocrystals. The formation of the individual nanocrystals from the heterometallic mesocrystal occurs through sequential decomposition and recrystallization events. The steps in the interconversion are observed by in situ and ex situ analytical techniques allowing a mechanism for carbide and metal formation to be proposed. The synthetic route is scalable and likely to be extendable to a wider range of bimetallic materials using the diverse range of Prussian blue analogues (PBAs) reported in the literature.

A Single Source, Scalable Route for Direct Isolation of Earth-Abundant Nanometal Carbide Water-Splitting Electrocatalysts

“…M-PBAs were prepared following literature precedence procedure using a coprecipitation reaction at room temperature . Briefly, the Co-PBA is synthesized by coprecipitation at room temperature.…”

“…M-PBAs were prepared following literature precedence procedure using a coprecipitation reaction at room temperature. 43 Briefly, the Co-PBA is synthesized by coprecipitation at room temperature. Aqueous 20 mM K 3 Co(CN) 6 solution (50 mL) and 50 mL of aqueous 0.1 M KCl were mixed together for 10 min.…”

“…In the literature, there are multiple synthetic routes to prepare metal carbide nanocrystals including high temperature decomposition routes of molecular precursors, ,,− carburization of metals and metal oxides, , and the recent demonstration of the thermal conversion of a metal organic framework or Prussian blue analogue (PBA) as single source precursors to the desired carbide. ,− While the use of high temperature M­(CO) 6 reactions to produce metal carbide precatalysts is reasonable in the laboratory, ,,, a synthetic route utilizing a single source precursor would be advantageous in the development of scalable and sustainable synthesis for industrial applications . PBAs can be converted to carbides and metals via calcining powders or solvothermally. ,− Researchers have shown pure phase carbides are isolable in Ni and Fe, but the isolated particles are insoluble and embedded in a carbonaceous layer. , …”

Metal Carbide Nanocrystal Nucleation and Growth in a Transition Metal Coordination Polymer

“…1,19−23 It was hypothesized that the growth mechanism to form the carbide nanocrystal follows a stepwise transformation initiated by amine attack at (111) corners with propagation along (100), (010), and (001) at defects, including glide plane lattice defects, vacancies, and delaminated surfaces. 1 It is reasonable to assume the formation of the metal carbide from the mesocrystal template can be described by nucleation theory, albeit with the constraint that for nucleation to occur, the loss of cyanamide (NCN) is required. The hypothesized growth behavior is similar to a solid-state transformation, which suggests the PBA to carbide could be modeled analogously using FW autocatalytic growth kinetics.…”

Self-standing heterostructured NiCx-NiFe-NC/biochar as a highly efficient cathode for lithium–oxygen batteries

“…Bimetallic Prussian blue analogues (PBAs) are metal organic framework (MOF) materials, which are promising precursors to prepare transition metal carbides with a porous cubic nanostructure exhibiting excellent catalytic properties [ 36 – 37 ]. Biomass materials can be used to prepare N-doped carbons since their proteins contain nitrogen atoms.…”