Ni₃S₂/Ni Heterostructure Nanobelt Arrays as Bifunctional Catalysts for Urea-Rich Wastewater Degradation

Abstract

Urea electrolysis is a cost-effective method for urea-rich wastewater degradation to achieve a pollution-free environment. In this work, the Ni3S2/Ni heterostructure nanobelt arrays supported on nickel foam (Ni3S2/Ni/NF) are synthesized for accelerating the urea oxidation reaction (UOR) and hydrogen evolution reaction (HER). It only needs ultralow potentials of 1.30 V and −54 mV to achieve the current density of ±10 mA cm–2 for UOR and HER, respectively. Meanwhile, the overall urea oxidation driven by Ni3S2/Ni/NF only needs 1.36 V to achieve 10 mA cm–2, and it can remain at 100 mA cm–2 for 60 h without obvious activity attenuation. The superior performance could be attributed to the heterostructure between Ni3S2 and Ni, which can promote electron transfer and form electron-poor Ni species to optimize urea decomposition and hydrogen production. Moreover, the nanobelt self-supported structure could expose abundant active sites. This work thus provides a feasible and cost-effective strategy for urea-rich wastewater degradation and hydrogen production.

Anodic Process of Nano-Ni Hydroxides for the Urea Oxidation Reaction and Its Electrochemical Removal with a Lower Energy Input

“…Nitrogen contaminants are energy-intensive for their proper treatments, and therefore nowadays the use of renewable energy inputs and sustainable processes is increasingly receiving attention. Electrochemical catalytic conversion toward their smaller molecules leading to energy saving is of importance in a variety of areas, including fuel cells, energy storage, wastewater treatment, and electrochemical sensors for medical, food, and environmental analysis. − Particularly, much attention has been paid to the electrolysis of urea-rich wastewater owing to its ability to produce hydrogen as an alternative fuel, while cleaning wastewater. − Direct urea fuel cells based on electro-oxidation of urea at the anode and oxidant (oxygen or hydrogen peroxide) reduction at the cathode have also been developed recently for the purpose of energy production accompanied by purifying urea-rich sewage. − …”

Co–Fe–B Nanochain Electrocatalysts for Oxygen Evolution at High Current Density

“…The OER performance of Co–Fe–B/NF is superior to that of transition metal-based boride catalysts recently described (Table S1). Tafel plots were used to determine the catalysts’ reaction kinetics (Figure b) . The Co–Fe–B/NF electrode exhibits a low Tafel slope (36 mV dec –1 ), which is much less than those of the Fe–B/NF (68 mV dec –1 ), Co–B/NF electrodes (109 mV dec –1 ), and bare NF (127 mV dec –1 ).…”

Electrochemical Reactivity Investigation of Urea Oxidation Reaction in Nichrome/Nitrogen Doped Carbon Nanofibers Synthesized by CVD Method

“…It can be seen that in the presence of urea in KOH at any given molarity, the current density increased at an onset potential of 0.4 V (vs. Ag/AgCl) in the forward anodic cycle signifying the activity of urea oxidation reaction. The anodic reaction can be given by Equation (1), [30–33] …”

“…It can be seen that in the presence of urea in KOH at any given molarity, the current density increased at an onset potential of 0.4 V (vs. Ag/AgCl) in the forward anodic cycle signifying the activity of urea oxidation reaction. The anodic reaction can be given by Equation ( 1), [30][31][32][33] The long term stability test implemented for NiCr NCNFs for 4000 s in O 2 saturated 1 M urea + 1 M KOH using chronoamperometry method at 0.7 V (vs Ag/AgCl) is presented in Figure 4b. The performance of NiCr NCNFs was found to be stable in a mixture of urea and KOH.…”