Honeycomb Carbon Nanofibers: A Superhydrophilic O -Entrapping Electrocatalyst Enables Ultrahigh Mass Activity for the Two-Electron Oxygen Reduction Reaction.

Electrocatalytic two-electron oxygen reduction has emerged as a promising alternative to the energy- and waste-intensive anthraquinone process for distributed H O production. This process, however, suffers from strong competition from the four-electron pathway leading to low H O selectivity. Herein, we report using a superhydrophilic O -entrapping electrocatalyst to enable superb two-electron oxygen reduction electrocatalysis. The honeycomb carbon nanofibers (HCNFs) are robust and capable of achieving a high H O selectivity of 97.3 %, much higher than that of its solid carbon nanofiber counterpart. Impressively, this catalyst achieves an ultrahigh mass activity of up to 220 A g , surpassing all other catalysts for two-electron oxygen reduction reaction. The superhydrophilic porous carbon skeleton with rich oxygenated functional groups facilitates efficient electron transfer and better wetting of the catalyst by the electrolyte, and the interconnected cavities allow for more effective entrapping of the gas bubbles. The catalytic mechanism is further revealed by in situ Raman analysis and density functional theory calculations.