One-step synthesis of NiS_2/rGO composite for efficient electrocatalytic urea oxidation

This work reveals that nickel disulfide and reduced graphene oxide can be integrated by one-step hydrothermal method. Compared to pure nickel disulfide, the prepared composite renders boosted electrocatalytic performance toward urea oxidation with high reaction rate constant and turnover frequency. Urea electrolysis receives increasing attention, because it can remediate urea-contaminated wastewater and produce hydrogen fuel simultaneously. Developing advanced catalysts for urea oxidation reaction is highly desirable but still challenging. In this work, we reveal that nickel disulfide (NiS_2) and reduced graphene oxide (rGO) can be successfully prepared by one-step hydrothermal reaction. NiS_2/rGO composite material is characterized to exhibit improved electrical conductivity and larger electrochemical active surface area, which hold the key to promote the reaction kinetics of urea oxidation. The overall reaction rate constant is determined as 2.88 × 10^5 cm^3 mol^−1 s^−1 for NiS_2/rGO, which is $$\approx$$ ≈ 75 times higher than that of NiS_2 counterpart (3.87 × 10^3 cm^3 mol^−1 s^−1). As a result, the NiS_2/rGO electrocatalyst demonstrates superior catalytic performance toward urea oxidation with high catalytic current responses (220 vs. 113 mA cm^−2 at 1.5 V), low Tafel slope (51 vs 87 mV dec^−1), and turn–over frequency (0.055 vs. 0.024 s^−1) in comparison with pure NiS_2. Moreover, NiS_2/rGO renders stable catatlytic performance in a 30,000 s test, addressing the crucial role of rGO in the composite sample. Graphical abstract