An iron phosphate hydroxide hydrate electrocatalyst: synergistic effects of Fe2+ and Fe3+ for enhanced hydrogen evolution reaction stability

Synthesized via unique electrodeposition, Fe 3 (PO 4 )(OH) 6 ·3H 2 O HER catalyst, with varied ratios, boasts enriched Fe 3+ /Fe 2+ sites. In 1 M KOH, it excels with a low 130 mV overpotential, 87 mV dec −1 Tafel value, and 80 hour durability at 100 mA cm −2 .