Electrochemical integration of amorphous NiFe (oxy)hydroxides on surface-activated carbon fibers for high-efficiency oxygen evolution in alkaline anion exchange membrane water electrolysis

Abstract

Developing practical water-splitting devices that convert earth-abundant solar energy and water into renewable fuel holds promise for a sustainable energy future; however, its successful commercialization for practical applications is limited by the sluggish kinetics of the oxygen evolution reaction (OER). Herein, we developed a high-efficiency and low-cost three-dimensional (3D) OER electrode via electrochemical integration of amorphous NiFeOOH on surface activated carbon fiber paper (CFP). The as-synthesized 3D-a-NiFeOOH/N-CFP electrode exhibits an ultra-low overpotential η(O₂) of 170 mV to afford 10 mA cm⁻² current density, together with a Tafel slope of 39 mV per decade, and excellent stability under OER conditions. Apart from the synergistic effect, the excellent OER activity of a-NiFeOOH/N-CFP is attributed to the unique 3D structure with enriched active sites and the improved electrical conductivity that facilitates the fast OER kinetics and mass transport properties. As a result, the catalyst achieves a high turnover frequency (TOF) of 0.99 s⁻¹ and mass activity (j_m) of 2527 A g⁻¹ at η(O₂) 270 mV, which outperforms so far reported state-of-the-art OER catalysts and commercial IrO₂. Besides, an alkaline anion exchange membrane water electrolyzer fabricated with the a-NiFeOOH/N-CFP anode delivers 1 A current at 1.88 V with a long-term durability of 240 h. These findings highlight the design of high-efficiency OER catalysts and significant advancements towards the utilization of NiFeOOH catalysts for commercial applications.