Ultrafast room-temperature activation of nickel foams as highly efficient electrocatalysts

Nickel foams (NF) are widely used electrode substrates that are associated with a wide range of industrial chains and large economic benefits. However, the pristine Ni foams usually possess poor electrochemical activities with dense passivation layers. Herein, an ultra-fast method for activating raw Ni foam was developed by soaking the Ni foam in a formulation solution of thiourea and I2/KI at room temperature for just a few minutes. In the solution, I3− (I2 + I−) acts as an oxidizer to accelerate the formation of Ni2+, while the hydrolysis of thiourea provides a weakly acidic environment and sulfur ions for formation of superficial layer NiS with I doping. The activated Ni foam has a fluffy nanosheet structure and the activity, characterized by the integrated Ni2+/Ni3+ peak area is enhanced by more than 100 times. The activated electrode exhibits high performance towards urea oxidation reaction (UOR) in alkaline electrolytes, delivering a current density of 100 mA cm−2 at only 1.44 V (vs. RHE, reversible hydrogen electrode). The in situ Raman spectroscopy identifies NiOOH as the catalytically active species for urea oxidation and in situ differential electrochemical mass spectrometry (DEMS) isotope tracking experiment reveals an intramolecular N-N bond coupling mechanism during the UOR. The developed activation method is easy to scale up for preparing large-area electrode and the catalytic activity is extended to oxidation of other organic molecules. This work presents a novel ultrafast one-step surface engineering strategy for activating Ni foams into high-performance electrocatalysts.