Achieving efficient urea electrolysis by spatial confinement effect and heterostructure

Urea oxidation reaction (UOR) can replace the oxygen evolution reaction (OER) at the anode in water elec-trolysis, 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 electro-catalyst, 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 nano -particles 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 (FeP)-P-2/(CoP)-P-2 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 (-1) in alkaline solution. Remarkably, the electrochemical activity of [Fe2P/Co2P]@Mo2S3/NF displays only slightly decay after 72 h durability test.

Automated summary

A binder-free self-standing composite electro-catalyst, consisting of a carbon layer containing Fe2P/Co2P nanoparticles on a nickel foam substrate with Mo2S3, has been innovatively designed and synthesized. This catalyst exhibits excellent catalytic performance for urea oxidation reaction, with low overpotential and high stability.