Surface functionalization of nickel foam with two-dimensional conjugated MOFs Fe3(hexaiminotriphenylene)2 for highly efficient oxygen evolution reaction

Abstract

The design of high-efficient, low-cost, and stable electrocatalysts for oxygen evolution reaction (OER) is highly demanding for energy conversion applications. Metal-organic frameworks (MOFs), with large surface area and flexible molecular species, can supply atom-dispersed metal active coordination sites (M−NX, M−SX, M−OX) for OER and have been regarded as potential catalysts for practical applications. However, it is still challenging to use MOFs as OER catalysts directly due to their low conductivity and poor stability. Herein, we successfully synthesized a 2D c-MOF of Fe3(HITP)2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) on the surface of nickel foam (NF) by using a layer-by-layer self-assembly strategy. The Fe3(HITP)2/NF-x electrode (x = 5, 10, 15, 20 is the number of cycles) exhibited impressive OER catalytic activity in alkaline electrolyte (1 M KOH), which is superior or comparable to most of the transition metal-based materials reported. Typically, Fe3(HITP)2/NF-15 were able to fully expose the Fe-N4 catalytic sites with an overpotential of 224 mV at a current density of 10 mA·cm−2 and a Tafel slope of 45.4 mV·dec-1. This was mainly attributed to the higher ECSA value, better kinetic process, and fast charge transfer ability of Fe3(HITP)2/NF. In addition, the current density of Fe3(HITP)2/NF-15 remained at 97.3 % of the initial current density after 24 h i-t stability test, showing excellent catalytic stability. This work provided a novel design strategy for the direct application of MOFs to OER applications.