Advancing Alkaline Water Electrolysis Using Electrochemical Reconstruction‐Driven Nickel Oxalate/Iron Oxide Heterostructure to Ni/Fe Hydroxide‐(Oxy)Hydroxide Electrocatalyst

The electrochemical reconstruction of heterostructures emerged as a striking strategy for crafting high‐performance electrode materials to boost the alkaline oxygen evolution reaction (OER). This work reports the synthesis of nickel oxalate/hematite (NiOX/Fe 2 O 3 ) heterostructure, exhibiting enhanced porosity, relocation of the electronic distribution, optimal hydrophilicity, and abundant Ni‐Fe heterojunctions. Upon electrochemical reconstruction, the heterostructure transforms into Ni/Fe hydroxide‐(oxy) hydroxide (named NiOX/Fe 2 O 3 ‐AP (after precondition)), demonstrating a significantly low overpotential of 234 ± 3 mV @10 mA/cm 2 geo compared to individual activated counterparts. In addition, the NiOX/Fe 2 O 3 ‐AP shows swift reaction kinetics and 100 h stability across 10–100 mA/cm 2 geo on redox‐inactive carbon paper. The comprehensive electrochemical studies of NiOX/Fe 2 O 3 ‐AP reveal that improved active site density, higher intrinsic activity, and facile charge migration play a key role in the noted better activity. Furthermore, NiOX/Fe 2 O 3 ‐AP displayed 90 ± 4% Faradaic efficiency and improved geometric competency compared to the physical mixture, emphasizing the importance of Ni/Fe synergy. Moreover, the inferior prowess of NiFe‐LDH and FeOOH compared to NiOX/Fe 2 O 3 ‐AP highlights the significance of the primitive Ni‐Fe heterojunction and their subsequent electrochemical reconstruction to Ni/Fe hydroxide‐(oxy) hydroxide. Finally, the electrolyzer was designed using NiOX/Fe 2 O 3 ‐AP as an anode and Pt/C as a cathode, which achieved 1.518 ± 0.006 V cell potential at 10 mA/cm 2 geo , sustaining 80 h across 10–100 mA/cm 2 geo .