Hierarchical “Core-shell” Electrocatalysts for the Oxygen Reduction Reaction (ORR) based on Graphene “Cores” and Metal Alloy Carbon Nitride “Shells”

The sluggish kinetics of the oxygen reduction reaction (ORR) is one of the most important bottlenecks in the operation of several families of advanced energy conversion and storage devices, such as metal-air batteries and low-temperature fuel cells (e.g., proton-exchange membrane fuel cells, PEMFCs and anion-exchange membrane fuel cells, AEMFCs). Accordingly, the development of efficient ORR electrocatalysts (ECs) is one of the most active research areas in this field. This work describes the features of a new family of ECs for the ORR, exhibiting a hierarchical “core-shell” morphology; they include a graphene-based nanostructured “core” covered by a carbon nitride “shell” embedding the ORR active sites in carbon- and nitrogen-based “coordination nests”. The proposed “core-shell” ORR ECs are obtained by customizing a unique and extremely flexible preparation protocol [1-3], that allows to fine-tune the morphology and the chemical composition of the ECs. This work overviews the synthetic strategies used to obtain the ECs comprising the graphene-based nanostructured “cores” and discusses the complex correlations existing between the preparation parameters, the physicochemical properties and the electrochemical performance. Finally, the most promising avenues and new directions for the research are indicated, with the aim to obtain ECs comprising graphene-based nanostructured “cores” exhibiting an improved ORR performance and durability, and at lower costs, in comparison with state-of-the art “reference” ECs. [1] V. Di Noto, E. Negro, K. Vezzù, F. Bertasi, and G. Nawn, Electrochem. Soc. Interface 24 (2015) 59-64. [2] V. Di Noto, E. Negro, A. Bach Delpeuch, F. Bertasi, G. Pagot, and K. Vezzù, Patent application 102017000000211, filled on 02 January 2017. [3] V. Di Noto, E. Negro, K. Vezzù, F. Bertasi, G. Nawn, L. Toncelli, S. Zeggio, and F. Bassetto, Patent application PCT/IB2016/055728, filled on 26 September 2016, priority date 28 September 2015.