Inner-pore reduction nucleation of palladium nanoparticles in highly conductive wurster-type covalent organic frameworks for efficient oxygen reduction electrocatalysis

Abstract

Covalent organic frameworks (COFs) have emerged as a class of promising supports for electrocatalysis because of their advantages including good crystallinity, highly ordered pores, and structural diversity. However, their poor conductivity represents the main obstruction to their practical application. Here, we reported a novel synthesis strategy for synergistically endowing a triphenylamine-based COFs with improved electrical conductivity and excellent catalytic activity for oxygen reduction, via the in-situ redox deposition and confined growth of palladium nanoparticles inside the porous structure of COFs using reductive triphenylamine frameworks as reducing agent; meanwhile, the triphenylamine unit was oxidized to radical cation structure and affords radical cation COFs with conductivity as high as 3.2*10−1 S m−1. Such a uniform confine palladium nanoparticle on highly conductive COFs makes it an efficient electrocatalyst for four-electron oxygen reduction reaction (4e-ORR), showing excellent activities and fast kinetics with a remarkable half-wave potential (E1/2) of 0.865 V and an ultralow Tafel slope of 39.7 mV dec−1 in alkaline media even in the absence of extra commercial conductive fillers. The generality of this strategy was proved by preparing the different metal and metal alloy nanoparticles supported on COFs (Au@COF, Pt@COF, AuPd@COF, AgPd@COF, and PtPd@COF) using reductive triphenylamine frameworks as reducing agent. This work not only provides a facile strategy for the fabrication of highly conductive COF supported ORR electrocatalysts, but also sheds new light on the practical application of Zn-air battery.