Nickel-iron in the second coordination shell boost single-atomic-site iridium catalysts for high-performance urea electrooxidation

Single-atom catalysts (SACs) with high catalytic activity as well as great stability are demonstrating great promotion in electrocatalytic energy conversion, which is also a big challenge to achieve. Herein, we proposed a facile synthetic strategy to construct nickel-iron bimetallic hydroxide nanoribbon stabilized single-atom iridium catalysts (Ir-NiFe-OH), where the nickel-iron hydroxide nanoribbon not only can serve as good electronic conductor, but also can well stabilize and fully expose single-atom sites. Adopted as catalyst for urea oxidation reaction (UOR), it exhibited excellent UOR performance that it only needed a low operated potential of 1.38 V to achieve the current density of 100 mA·cm−2. In-situ Fourier transform infrared spectroscopy, X-ray absorption spectrum, and density functional theory calculations proved that Ir species are active centers and the existence of both Ni and Fe in the local structure of Ir atom can optimize the d-band center of Ir species, promoting the adsorption of intermediates and desorption of products for UOR. The hydrogen evolution reaction (HER)/UOR electrocatalytic cell demanded voltages of 1.46 and 1.50 V to achieve 50 and 100 mA·cm−2, respectively, which demonstrated a higher activity and better stability than those of conventional catalysts. This work opens a new avenue to develop catalysts for UORs with boosted activity and stability.