Tertiary-Amine-Assisted Synthesis of Hierarchical Porous Nitrogen-Incorporated Cobalt–Iron (Oxy)hydroxide Nanosheets for Improved Oxygen Evolution Reaction

Transition-metal (oxy)­hydroxides are cost-efficient and high-performance catalysts for electrochemical water splitting in terms of the conversion and storage of clean and renewable energy. Rational design and synthesis of desired electrocatalysts for the oxygen evolution reaction (OER) is of great significance toward water electrolysis. Herein, by employing a tertiary amine triethanolamine with good chemical stability and slight alkalinity as the precipitant, we show a one-step route for the fabrication of hierarchical porous nitrogen-incorporated cobalt–iron (oxy)­hydroxide (N-CoFe-O x H y ) nanosheets with microporous, mesoporous, and macroporous structures in the catalyst. The as-obtained hierarchical porous N-CoFe-O x H y nanosheets possess a larger specific surface area, more active sites, faster charge transfer, and higher intrinsic activity than those prepared by using a conventional precipitant such as urea. The N-CoFe-O x H y catalyst exhibits a superior electrocatalytic OER performance with an overpotential of 253 mV at 10 mA/cm2, a Tafel slope of 41 mV/dec, and long-term durability. Besides, such a hierarchical porous N-CoFe-O x H y OER electrocatalyst was applied in a two-electrode electrochemical cell with Pt/C as the cathode to generate hydrogen and a solar-to-hydrogen system, demonstrating a low cell voltage of 1.53 V at 10 mA/cm2, an outstanding stability, and the feasibility of developing non-noble-metal (oxy)­hydroxide OER catalysts in practical hydrogen production via solar-driven unbiased water splitting. This work affords a facile strategy to modulate the morphology and activate the intrinsic active sites toward the rational design of earth-abundant, low-cost, and high-efficiency catalysts for clean and renewable energy production.