Cobalt Phosphide Decorating Metallic Cobalt With a Nitrogen-Doped Carbon Nano-Shell Surpasses Platinum Group Metals for Oxygen Electrocatalysis Applications

Abstract

It has been a long-standing challenge to cultivate capable and resilient oxygen electrocatalysts with higher activity, low price, and long lifetime to replace the commonly used platinum group metals, i.e., Pt for oxygen reduction reaction (ORR) and RuO₂/IrO₂ for oxygen evolution reaction (OER). This work presents a promising approach to address the challenges associated with oxygen electrocatalysis by introducing a cobalt phosphide/metallic cobalt (Co₂P/Co) core wrapped in a nitrogen-doped conductive carbon (CN) nano-shell, demonstrated as Co₂P/Co@NC. The strong chemical bonding between metallic cobalt and phosphorus, nitrogen and conductive carbon contributes to the enhanced conductivity and stability of the electrocatalyst. The nitrogen doping in the carbon shell provides additional Co–N active sites, which are crucial for ORR activity. Co₂P/Co@NC demonstrates promising activity and stability compared to noble metals such as Pt for ORR in an alkaline medium. This suggests its potential as a cost-effective alternative to Pt-based catalysts. Further, due to factors such as strong cobalt-phosphide bonding, high cobalt oxidation states and excellent conductivity of the nitrogen-doped carbon shell, the Co₂P/Co@NC outperforms noble metal oxides like iridium dioxide (IrO₂) and ruthenium dioxide (RuO₂) for OER. Co₂P/Co@NC exhibits a low potential difference of 0.63 V, which is among the lowest reported for bifunctional electrocatalysts capable of both ORR and OER. Overall, the described strategy offers a promising avenue for developing efficient, low-cost and stable electrocatalysts for oxygen reactions, which are crucial for various electrochemical energy conversion and storage technologies, such as fuel cells and metal–air batteries.