Bifunctional Ni1-xFex layered double hydroxides/Ni foam electrodes for high-efficient overall water splitting: A study on compositional tuning and valence state evolution

摘要

Toward both hydrogen (HER) and oxygen evolution reaction (OER) in alkaline electrolyte, bifunctional Ni1-xFex,, layered double hydroxides (LDHs) on Ni foam (NF) have been systematically developed for high-efficient water splitting by changing Fe content. The interlaced NiFe LDHs nanosheets consist of ultra-small gamma-NiOOH-like nanoparticles with size of 2-5 nm interconnected by amorphous domains. By tuning Fe content from 15% to 25% and 36%, optimized p.3.0 values (mu(10) is the overpotential required to reach a current density of 10 mA/cm(2)) of 169 mV (HER) and 140 mV (OER), and Tafel slope of 31 mV/dec have been achieved at x = 0.25. A hydrogen generation rate of 170 mu mol/h/cm(2) with H-2/O-2 ratio nearly to 2:1 and Faradic efficiency of 93% have been realized at 1.7 V by using two Ni0.75Fe0.25 LDHs/NF as respective anode and cathode in a 2-electrode system. Based on the valence state evolution of the electrodes, undergoing respectively H-2 and O-2 generation, tremendous transformation of NiFe(OH)(2) to NiFeOOH is deduced, which reaches a Ni3+/Ni2+ ratio of similar to 2.35 for the Fe content of 25%. Further or less Fe incorporation will depress the electrocatalytic property. The effective Ni3+ active sites on the NiFe-based nanosheets endow the Ni0.75Fe0.25 LDHs/NF with high bifunctional catalytic property. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.