Structural Instability of NiFe-Layered Double Hydroxide Nanosheets during Water Oxidation Operation

NiFe-layered double hydroxide (NiFe-LDH) stands out as a promising electrocatalyst for the oxygen evolution reaction (OER), but the structural transformations under OER conditions are not well understood. The structural evolution of highly crystalline NiFe-LDH on nickel foam during OER testing in 1 M KOH solution was analyzed using IR, Raman, XRD, XPS techniques, and DFT calculations. Instability of interlayer species within the NiFe-LDH, including protons, anions, and water molecules, was found to cause the crystal structure to undergo expansion or contraction during OER operation, decreasing crystallinity and roughening the LDH surface. This dynamic structural evolution is crucial for determining OER activity, and it was observed that surface structural changes of the LDH, along with Fe content, jointly determined the degree of change in its OER activity. Our findings provide insights into designing active water-splitting electrocatalysts and highlight the relationship between OER activity and the structure of NiFe-LDH.