Revealing the early-stage deprotonation of Polyoxometalate on NiFe LDH for alkali oxygen evolution reaction

Layer double hydroxides (LDHs) often undergo surface reconstruction under oxidative potential during electrocatalytic oxygen evolution reaction (OER) to form the active phase of oxyhydroxides through deprotonation of LDHs. The early-stage deprotonation to form the active phase is crucial for OER electrocatalysts with high activity, yet effective approach to modulate is still difficult. Herein, we intercalated phosphomolybdate (PMo₁₂O₄₀)^3- into NiFe LDH interlayer space which modulated the electronic states of Ni and Fe in the MO₆ layer. The potential dependent Raman spectroscopic analysis reveals the early-stage phase transition from hydroxide to oxyhydroxide active phase, which was also verified by theoretical calculations. The intermolecular electron transfer from Fe to phosphomolybdate ion and the hydrogen attraction from the oxygen rich phosphomolybdate ion thus increased the contents of Fe³⁺, making the formation of oxyhydroxides active phase (γ-NiOOH) more feasible. These findings reveal that the large anion intercalation to LDH is an effective approach to control the phase transition.