Bifunctional Ni3S2 nanoflake/NiMoO4 nanoneedle composite electrocatalysts for efficient urea oxidation and hydrogen evolution in sustainable water electrolysis

초록

Hydrogen production through water electrocatalysis is hindered by the slow anodic oxygen evolution reaction (OER), which requires a high overpotential. To address this issue, the urea oxidation reaction (UOR) has garnered considerable attention as a promising and sustainable clean energy technology due to its low overpotential. In this study, we propose a rapid synthesis method for bifunctional Ni3S2/NiMoO4 composite catalysts using microwave. The fabricated Ni3S2/NiMoO4 catalysts demonstrate excellent applicability for both the UOR and the hydrogen evolution reaction (HER) under urea conditions, exhibiting superior activity due to the strong interaction between Ni3S2 and NiMoO4. The composite of Ni3S2 nanoflakes and NiMoO4 nanoneedles, expose abundant high-activity catalytic sites and enhances conductivity, facilitating rapid transfer of electrons to active sites. Conclusively, the optimal Ni3S2/NiMoO4 catalyst required only 1.37 V for the UOR and an overpotential of 0.23 V for the HER at a current densitiy of 100 mA cm-2 in a mixture of urea and KOH. Remarkably, overall urea splitting required only 1.5 V at a current density of 10 mA cm- 2, utilizing the Ni3S2/NiMoO4 catalyst as both anode and cathode. Furthermore, the Ni3S2/NiMoO4 electrode demonstrated sustained stability over 100 h of UOR and HER, indicating its significant capability for efficient hydrogen production. Additionally, the optimal catalyst exhibited outstandingly low voltage of 2.1 V at a current density of 1.0 A cm- 2 in a single cell electrolyzer at 60 degrees C, and remains stable for 100 h.

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