Three-Dimensional Smart Catalyst Electrode for Oxygen Evolution Reaction

A multifunctional catalyst electrode mimicking external stimuli-responsive property has been prepared by the in situ growth of nitrogen (N)-doped NiFe double layered hydroxide (N-NiFe LDH) nanolayers on a 3D nickel foam substrate framework. The electrode demonstrates superior performance toward catalyzing oxygen evolution reaction (OER), affording a low overpotential of 0.23 V at the current density of 10 mA cm^-2, high Faradaic efficiency of ≈98%, and stable operation for >60 h. Meanwhile, the electrode can dynamically change its color from gray silver to dark black with the OER happening, and the coloration/bleaching processes persist for at least 5000 cycles, rendering it a useful tool to monitor the catalytic process. Mechanism study reveals that the excellent structural properties of electrode such as 3D conductive framework, ultra thickness of N-NiFe LDH nanolayer (≈0.8 nm), and high N-doping content (≈17.8%) make significant contribution to achieving enhanced catalytic performance, while N-NiFe LDH nanolayer on electrode is the main contributor to the stimuli-responsive property with the reversible extraction/insertion of electrons from/into N-NiFe LDH leading to the coloration/bleaching processes. Potential application of this electrode has been further demonstrated by integrating it into a Zn-air battery device to identify the charging process during electrochemical cycling.