One-step and scalable synthesis of Ni2P nanocrystals encapsulated in N,P-codoped hierarchically porous carbon matrix using a bipyridine and phosphonate linked nickel metal-organic framework as highly efficient electrocatalysts for overall water splitting

The development of highly active and durable noble-metal-free electrocatalysts for overall water splitting is a great challenge. Herein, a microdroplet flow reaction is used for ultrafast and continuous synthesis of a nickel metal-organic framework material with 4,4'-bipyridine and phosphonate ligands. A one step pyrolysis of this metal-organic framework to various heat treatment temperatures and hold times at maximum temperature give a range of electrocatalysts, containing crystalline Ni2P nanoparticles dispersed in a porous carbonaceous matrix incorporating relatively high concentrations of both nitrogen and phosphorus derived from the original metaleorganic framework. The Ni2P electrocatalysts inherite the morphology of the metal-organic framework precursor, have a uniform dispersion of Ni2P sites and Brunauer-Emmett-Teller surface areas in the range 558-754 m(2) g(-1). The Ni2P electrocatalysts exhibit excellent catalytic performance for both hydrogen and oxygen evolution reactions in 1.0 M KOH and an electrolyzer using Ni2P electrocatalysts as both cathode and anode generates a current density of 10 mA cm(-2) at a voltage of 1.62 V with superior durability. This facile and scalable synthesis strategy for the rational design of electrocatalysts represents a proof-of-concept with the potential for scale-up for use in practical applications. (C) 2018 Elsevier Ltd. All rights reserved.