N,P co-doped hollow carbon nanofiber membranes with superior mass transfer property for trifunctional metal-free electrocatalysis

Abstract Carbon-based metal-free electrocatalysts have inspired extensive efforts to explore their applications in many nontrivial electrochemical reactions, such as oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER), by virtue of the integrated advantages including low cost, sustainability, longevity, and multifunctionality. Herein, N,P co-doped hollow carbon nanofiber (N,P–HCNF) membranes were facilely prepared via coaxial electrospinning technology, which are bestowed with a hierarchical porous architecture, turbostratic structures, and abundant catalytically active sites such as doping, defects, and edges. Benefiting from structural features of the one-dimensional (1D) carbon hollow nanoarchitecture, which affords plentiful active sites, continuous conducting pathways, and benign mass transfer channels, the resultant catalyst reveals an excellent trifunctional electrocatalytic activity for ORR, OER, and HER. Impressively, it exhibits one of the best metal-free bifunctional electrocatalytic activities in oxygen electrocatalysis as characterized by a low potential deviation (ΔE) of 0.73 V between the half-wave potential (E 1/2) for ORR and the potential reaching 10 mA cm−2 (Ej=10) for OER. Significantly, further investigations demonstrate that the effect of mass transfer makes a great difference to electrocatalytic activity, mainly through enlarged specific surface area to affect intrinsic catalytic activity and the ionic resistance in pores. This work sheds light on the design, fabrication, and regulation of highly active metal-free electrocatalysts with abundant active sites and tuned pore structures for electrocatalysis and other applications.