Achieving efficient urea electrolysis by spatial confinement effect and heterostructure

Abstract

Urea oxidation reaction (UOR) can replace the oxygen evolution reaction (OER) at the anode in water electrolysis, which can reduce the thermodynamic potential of electrochemical water splitting. Currently, UOR performance is mainly limited by the 6 e− transfer process, requiring high-performance catalysts to reduce overpotential. Here, we innovatively designed and synthesized a binder-free self-standing composite electrocatalyst, viz. a carbon layer containing Fe2P/Co2P nanoparticles on a nickel foam substrate with Mo2S3 ([Fe2P/Co2P]@Mo2S3/NF). FeCo-prussian blue analogue (PBA)/nickel foam (NF) was obtained from cobalt-based metal–organic frameworks (Co-MOFs) by anion exchange at room temperature, and then [Fe2P/Co2P]@Mo2S3/NF was derived through high-temperature phosphating and hydrothermal treatment of FeCo-PBA/NF. After high-temperature phosphating treatment, FeCo-PBA collapses to form a carbon layer tightly wrapping on the NF skeleton. The carbon layer has a confinement effect on Fe2P/Co2P nanoparticles, preventing the nanoparticles from agglomerating and deactivating. Simultaneously, Fe2P/Co2P/NF and Mo2S3 form a heterostructure to optimize the electronic structure and accelerate electron transfer and urea activation, and make metal phosphides prone to interfacial oxidation during UOR catalysis. The internal carbon layer containing Fe2P/Co2P nanoparticles acts as a conductive support for better electron transfer from the interior to the exterior metal hydroxide/oxyhydroxide species and Mo2S3 species. The synergistic interaction amang Fe2P/Co2P, hydroxide/oxyhydroxide and Mo2S3 enhances the catalytic performance of [Fe2P/Co2P]@Mo2S3/NF. Strong hydrophilicity and superaerophobicity are conducive to electrolyte immersion and bubble detachment, which further promotes the [Fe2P/Co2P]@Mo2S3/NF catalyst to exhibit excellent UOR catalytic performance, only requiring potential of 1.36 V (vs. RHE) at 100 mA cm−2 with low Tafel slope of 41.5 dec−1 in alkaline solution. Remarkably, the electrochemical activity of [Fe2P/Co2P]@Mo2S3/NF displays only slightly decay after 72 h durability test.