Photo-Excited High-Spin State Ni (III) Species in Mo-Doped Ni 3 S 2 for Efficient Urea Oxidation Reaction.

Designing robust catalysts for increasing the sluggish kinetics of the urea oxidation reaction (UOR) is challenging. Herein, the regulation of spin states for metal active sites by photoexcitation to facilitate the adsorption of urea and intermediates is demonstrated. Mo-doped nickel sulfide nanoribbon arrays (Mo-Ni 3 S 2 @NMF) with excellent light-trapping capacity are successfully prepared. Under AM 1.5G illumination, the activity of the Mo-Ni 3 S 2 @NMF exhibits a 50% improvement in the UOR current. Compared with those under dark conditions, Mo-Ni 3 S 2 @NMF achieve 10 mA cm -2 at 1.315 V RHE for UOR and 1.32 V cell for urea electrolysis, which are decreases of 15 and 80 mV, respectively. The electron spin resonance, in situ Fourier transform infrared spectroscopy analysis and density functional theory calculations reveal that illumination led to the formation of Ni 3+ active sites in a high-spin state, which strengthens the d-p orbital hybridization of Ni-N, hence facilitating the adsorption of urea. C─N cleavage of the * CONN intermediate is further inhibited, which promotes the oxidation of urea molecules via the active N 2 pathway, thereby accelerating the UOR rate.