Ultra-small Ru nanoparticles embedded on Fe–Ni(OH)2 nanosheets for efficient water splitting at a large current density with long-term stability of 680 hours

Abstract

Pursuing highly active and stable bifunctional electrocatalysts for the hydrogen/oxygen evolution reaction (HER/OER) is significantly important for overall water splitting. Herein, we prepare an electrocatalyst of ultra-small Ru nanoparticles embedded on Fe–Ni(OH)₂ nanosheets in situ grown on a Ni foam (RuFe@NF) by a one-pot room temperature immersion method. The RuFe@NF only needs an overpotential of 28 mV to attain 10 mA cm⁻² towards the HER and an overpotential of 265 mV to deliver 50 mA cm⁻² for the OER in 1 M KOH solution. When RuFe@NF is used as both the cathode and anode for an overall water splitting electrolytic cell, it exhibits a relatively low cell voltage of 1.54 V to obtain 10 mA cm⁻². Impressively, the RuFe@NF based electrolytic cell exhibits ultra-long stability over 680 hours at 10 mA cm⁻² and even at larger current density up to 100 mA cm⁻², which is obviously superior to the noble “Pt/C‖IrO₂” couple (i.e., 180 mV voltage increase at 50 mA cm⁻² after 36 h), ranking the top among the water splitting catalysts previously reported thus far. The integrated electrode possesses different highly active HER and OER sites and a robust in situ network structure, which collectively improves the electron transport and therefore achieves high activity and stability of the RuFe@NF at an elevated current density. This work offers an alternative bifunctional electrocatalyst, which can be widely extended to large-scale water splitting technology.