Location effects of vanadium in NiFe layered double hydroxides for oxygen evolution reaction†

NiFe layered double hydroxides (NiFe-LDHs) have been widely acknowledged as a promising anode electrocatalyst in alkaline oxygen evolution reactions (OERs), and vanadium has demonstrated its capability to improve their OER performance. Considering that V can exist as three vanadium-based species, i.e., doped V^III in LDH laminates, intercalated VO₃⁻ between LDH interlayers, and free VO₃⁻ as an additive in KOH electrolyte, we systematically studied and compared their effects in determining the OER performance of NiFe-LDHs. Electrochemical results reveal that all three conditions mentioned above individually can improve the OER performance of NiFe-LDHs. When two of these conditions are present at the same time, the combination of VO₃⁻ intercalated into LDHs as the catalyst and free VO₃⁻ as the additive in KOH electrolyte shows the best OER performance, even exceeding the performance exhibited by the combination of all three conditions. Ex situ Raman results indicate that VO₃⁻ intercalation triggers an active γ-phase formation of NiFe-LDHs; in situ Raman data further reveal that VO₃⁻ as an electrolyte additive stabilizes this active phase and slows down the dissolution of LDHs, as supported by inductively coupled plasma characterization.