Nitrogen, Phosphorus, and Fluorine Tri-doped Graphene as a Multifunctional Catalyst for Self-Powered Electrochemical Water Splitting.

Abstract

Electrocatalysts are required for clean energy technologies (for example, water-splitting and metal-air batteries). The development of a multifunctional electrocatalyst composed of nitrogen, phosphorus, and fluorine tri-doped graphene is reported, which was obtained by thermal activation of a mixture of polyaniline-coated graphene oxide and ammonium hexafluorophosphate (AHF). It was found that thermal decomposition of AHF provides nitrogen, phosphorus, and fluorine sources for tri-doping with N, P, and F, and simultaneously facilitates template-free formation of porous structures as a result of thermal gas evolution. The resultant N, P, and F tri-doped graphene exhibited excellent electrocatalytic activities for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). The trifunctional metal-free catalyst was further used as an OER-HER bifunctional catalyst for oxygen and hydrogen gas production in an electrochemical water-splitting unit, which was powered by an integrated Zn-air battery based on an air electrode made from the same electrocatalyst for ORR. The integrated unit, fabricated from the newly developed N, P, and F tri-doped graphene multifunctional metal-free catalyst, can operate in ambient air with a high gas production rate of 0.496 and 0.254 μL s-1 for hydrogen and oxygen gas, respectively, showing great potential for practical applications.