Synthesis and Surface Chemistry of Bimetallic Chromium-Iron Carbide (CrxFe1-x)7C3 Solid Solution Nanoparticles

Abstract

A series of hexagonal (CrxFe1-x)7C3 solid solution compounds were synthesized for the first time as nanomaterials using a unique amine-metal oxide composite (AMOC) method. These materials are related to stainless steel where chromium provides protection from oxidation and could be potential low-cost catalyst materials for a variety of important reactions. Thus, a simple synthesis method coupled with a detailed understanding of their surface chemistry and composition is extremely important. X-ray photoelectron spectroscopy (XPS) studies revealed that both Fe and Cr in the bulk of (CrxFe1-x)7C3 solid solutions are mostly metallic. Further, the surface of these nanomaterials maintained exposed zero valent metals (∼10 at%) after long term air exposure demonstrating the corrosion and oxidation resistant nature of this Cr-Fe-C ternary system. This suggests that these compounds have stable surface chemistry which makes them potentially good candidates for catalysts. These bimetallic carbides were subsequently tested as electrochemical catalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) applications in acidic (0.1 M HClO4) and alkaline (0.1 M KOH) electrolytes. All (CrxFe1-x)7C3 solid solutions exhibit better ORR and OER activities than Cr7C3, Fe3C, and Co3O4 and both (Cr0.4Fe0.6)7C3 and (Cr0.5Fe0.4)7C3 are good OER catalysts in alkaline media demonstrating their potential for future catalysis applications.