One-step synthesis of carbon nanospheres with an encapsulated iron-nickel nanoalloy and its potential use as an electrocatalyst

Abstract

For many years, in electrochemical processes, carbon nanostructures with metal support have been employed as electrodes due to their high surface area, chemical stability, and excellent performance as catalyst support by allowing a better electronic transfer. Nevertheless, on the surface, metallic nanoparticles are susceptible to corrosion. Instead, by encapsulating individual nanoparticles, they are protected. Among the carbon nanostructures, the most common are graphene, carbon nanotubes (CNTs), and carbon nanospheres (CNSs). Unlike CNTs and CNSs, graphene is difficult to obtain in mass production, limiting their applications. Regarding CNTs and CNSs, the latter presents better catalytic activity. Nonetheless, the process of synthesis of CNSs with metal inside is commonly made by time-consuming autoclave processes, some involving more than 43 h, and hence are expensive. Here, we suggest an advantageous synthesis of CNSs with an iron–nickel alloy encapsulated inside, by using a one-step chemical vapor deposition (CVD) process in less than 3 h. This material has potential applications for environmental and energy processes. According to the authors, the uses of iron-nickel alloys as an electrocatalyst for the ammonia oxidation reaction has not been proved. Thus, we evaluate the composite as an electrocatalyst for the ammonia oxidation reaction, an electrochemical process that offers environmental remediation and hydrogen as a fuel. The electrochemical characterization shows that the use of a bimetallic electrode improves the catalytic activity. In this case, nickel is the active specie and iron is the metal added which reduces the reaction potential. Besides, the composite presents high specific capacitance, better than other materials proposed such as graphene decorated with FeNi alloys. This behavior can be related to the variation of the catalyst morphology (supported vs. encapsulated) by improving the catalyst dispersion and particle size stabilization.

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