Concentration-dependent effects of iron impurities on nickel electrodes for hydrogen evolution reaction in alkaline media

Effects of iron impurities on the alkaline hydrogen evolution reaction (HER) for nickel-based electrodes are not fully understood. Iron deposits on the Ni surface can either enhance HER kinetics by increasing surface roughness or act as a protective layer against NiH formation. This work systematically evaluates how different iron concentrations in the electrolyte affect HER activity and durability of polycrystalline Ni in 0.1 M KOH. Initial HER activity differences between 0 and 14 ppm Fe z + species are marginal. However, during 24-h chronopotentiometry tests at i = − 10 mA cm geo ‐ 2 lower iron concentrations (0–3 ppm) cause pronounced deactivation, while higher concentrations (6–14 ppm) maintain more stable operation. Combining structural and electrochemical analyses we link HER overpotential changes to accessible Ni sites, instead of surface roughness. This study shows a critical Fe z + impurity threshold ( ≥ 6 ppm ) in the electrolyte to exploit the beneficial effects of iron on HER durability of alkaline water electrolysis. • Unveiling fundamental Fe z + concentration-dependent HER effects for Ni electrodes. • Low Fe z + causes island deposits, exposes more Ni and facilitates deactivation. • High Fe z + leads to denser and protective films and retains the HER activity. • Detailed HER degradation model of Ni electrodes due to trace iron ion concentrations.