Protein-enriched fish "biowaste" converted to three-dimensional porous carbon nano-network for advanced oxygen reduction electrocatalysis

Highlights: • Porous carbon network was prepared by fish-scale pyrolysis and activated by ZnCl₂. • This carbon network exhibits good ORR catalytic activity and stability in alkaline condition. • The formation of three-dimentional network can facilitate the enhancement of ORR activity. • Pyridinic- and graphitic-N may be mainly responsible for the electrocatalytic activity. - Abstract: Recycling and utilizing organic biowastes will effectively help to decrease the damage to the natural environment and synchronously facilitate the development of new carbon materials for energy applications. In this study, we directly convert protein-rich fish-scale biowaste to hierarchically porous three-dimentional (3D)-network nanocarbons via two-step pyrolysis process combined with ZnCl₂ activation and acidic-treatment. It is interestingly found that this material exhibits more excellent oxygen reduction electrocatalytic activity and stability compared to the commercial 20 wt% Pt/C catalyst in both alkaline and acidic solutions, which can be closely correlated to its chemical state of nitrogen atoms, BET surface area and inner porous structure. The addition of ZnCl₂ activator during pyrolysis process can help to produce the 3D network nanostructure and then to enhance the mesopore surface area, making for the improvement of oxygen reduction performance. More remarkably, the ORR onset potential on our material is about 60 mV higher than that on the Pt/C catalyst in alkaline electrolyte. In addition, we also propose that pyridinic- and graphitic-nitrogen species may be key factors to be responsible for the electrocatalytic activity. This study can encourage the exploration of high porosity nanocarbons from widely-existed biowastes, functioning as highly active and stable oxygen reduction electrocatalysts.