Tunable Fe-Ni metal-organic framework electrocatalysts via post-synthetic iron incorporation for alkaline oxygen evolution

The oxygen evolution reaction (OER) remains a major kinetic bottleneck in sustainable hydrogen production via water electrolysis, driving the need for low-cost alternatives to noble-metal catalysts. Here, we report a facile, room-temperature, spontaneous cation-exchange strategy to incorporate iron into amorphous nickel-benzene-1,3,5-tricarboxylate (Ni-BTC), thereby enhancing its OER activity. By systematically varying the immersion time (6–48 h) and nominal Fe loading (5.47 wt, 9.02 wt, 15.38 wt%), we identified a volcano-type dependence of OER activity in both parameters. Specifically, activity increases with immersion time until 20 h, then declines at 48 h. Similarly, it peaks at an Fe loading of 9.02 wt% (48 mg) before dropping sharply at 15.38 wt% (88 mg). This decline at higher loadings is caused by blocking layers, as evidenced by the disappearance of Ni 3+ species and the emergence of an O 1 s shake-up satellite, which hinder charge transfer. The best performing (9.02 wt%) 48-Fe/Ni-BTC (20 h) catalyst achieves an overpotential of ~ 281.3 mV, outperforming the benchmark IrO 2 (~ 359.6 mV) and amorphous Ni-BTC (~ 355.8 mV). This facile, room-temperature, controlled doping route offers a practical strategy for enhancing Ni-based MOF electrocatalysts, though Operando structural evolution and post-OER characterization remain to be established. Ultimately, these findings provide a controlled framework for the rational design of MOF-based OER catalysts towards sustainable hydrogen production.