Cobalt Phosphate Interlayer to Enhance the Activity and Stability of the NiFe-LDH Anode in an Anion Exchange Membrane Water Electrolyzer

The development of oxygen evolution reaction (OER) catalysts based on non-noble metals that have high catalytic activity and long-term stability is crucial for the use of an anion exchange membrane water electrolyzer (AEMWE). Here, we report a three-layer composite OER catalyst, NiFe-LDH/CoPi/NF, with the cobalt phosphate (CoPi) interlayer in the middle of nickel foam and a NiFe-LDH nanosheet array. The CoPi interlayer significantly improves the OER catalytic activity as well as the stability. The overpotential required for NiFe-LDH/CoPi/NF to achieve an OER current density of 1000 mA·cm^-2 is only 277 mV, and the performance has almost no attenuation for 1000 h of continuous working at 1000 mA·cm^-2. The AEMWE using NiFe-LDH/CoPi/NF as an anode reached a current density of 1 A·cm^-2 at the cell voltage of only 1.709 V, and it stably operated up to 1200 h. It is found that the CoPi interlayer modulated the morphology of the NiFe-LDH nanosheet arrays and also tuned the electronic structure of the NiFe-LDH. The Ni in NiFe-LDH/CoPi/NF shows a higher valence state, thereby promoting its activity, and also shows a low dissolution rate, thereby promoting its stability.