Silica-Encapsulated Cobalt Nanoparticles Supported on Nitrogen-Doped Carbon Nanotubes as a Catalyst for Oxygen Reduction Reaction

One of the greatest sources of concern for the implementation of fuel cell (FC) technology is the sluggish kinetics of the oxygen reduction reaction (ORR), which is predominantly catalyzed with expensive Pt-based catalysts. Herein, a novel non-noble metal catalyst was synthesized by depositing silica-encapsulated cobalt nanoparticles (NPs) on nitrogen-doped carbon nanotubes (Co@SiO2/N/MWCNT). A variety of physical characterization methods were employed to study the structure and composition of the catalyst material. Silica encapsulation was found to hinder the decomposition of the electrochemically active surface area of the metal. The encapsulation into a silica shell allows the cobalt NP surface to remain without any major signs of oxidation or adsorption of functional groups, which may reduce the catalytic activity of the material. It was observed that nitrogen doping of carbon and the formation of catalytically active functional groups made a positive contribution to the material's electrocatalytic activity. Electrocatalytic properties were studied in 0.1 M KOH solution using the rotating disc electrode method. Co@SiO2/N/MWCNT presented excellent catalytic activity toward the ORR, with an onset potential of 0.97 V vs reversible hydrogen electrode, a half-wave potential of 0.84 V, and a limiting current density of around -7.3 mA cm-2. The results pave the way for the synthesis of silica-encapsulated metal NPs, their anchoring onto heteroatom-doped nanocarbons, and usage of the catalyst for FCs and other electrochemical applications.