NiFe Bimetallic Doped Geopolymer Catalyst for Hydrogen Evolution and Overall Water Splitting

Achieving efficient overall water splitting with non-precious metal catalysts remains a significant challenge due to the sluggish kinetics of both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Herein, we report a nickel–iron bimetallic doped geopolymer electrocatalyst (Ni0.9Fe0.1-GP) fabricated via a one-step alkali activation method on 316L stainless steel. Structural characterizations reveal that Fe3+ incorporation alters the distribution of Na+ and Ni2+ within the geopolymer network and modulates the Ni electronic structure. Electrochemical measurements show that Ni0.9Fe0.1-GP delivers an HER overpotential of 332.42 mV and an OER overpotential of 227.31 mV at 10 mA cm−2, outperforming Ni-GP and bare 316L SS. The practical operating voltage of Ni0.9Fe0.1-GP is 1.81 V, while the two-electrode electrolyzer delivers a comparable current density at 1.90 V (after accounting for uncompensated system resistances). Long-term stability tests demonstrate the superior durability of Ni0.9Fe0.1-GP during HER, OER, and overall water splitting. Mechanistic studies reveal the dual role of Fe3+: substantially increasing the electrochemical active surface area (ECSA) while modulating the Ni electronic structure, and improving structural stability through strong chemical anchoring within the geopolymer network. This work provides new insights into cost-effective bifunctional electrocatalysts and expands the application of geopolymers as functional catalytic supports for water splitting.