Highly Dispersed Core–Shell Ni@NiO Nanoparticles Embedded on Carbon–Nitrogen Nanotubes as Efficient Electrocatalysts for Enhancing Urea Oxidation Reaction

Abstract

Wastewater treatment and energy production are important fields of research to meet the current requirements of sustainable energy development and wastewater restoration. The urea oxidation reaction (UOR) can be used for simultaneous environmental remediation and energy production on a priority basis. Nickel−nickel oxide (Ni@NiO) core−shell NPs on carbon−nitrogen nanotubes (CNNTBs) have been synthesized as electrocatalysts by using a simple and easy aerial annealing method. Morphological analysis by high resolutiontransmission electron microscopy (HR-TEM) confirms the formation of Ni@NiO NPs on CNNTBs with an average size of ∼40 nm. Powder X-ray diffraction (XRD) confirms Ni@ NiOCN-X with a face-centered cubic (FCC) crystal structure. A BET surface area measurement suggests that annealing at 400 °C (Ni@NiOCN-4) creates a larger surface area than that of carbon−nitrogen material (CN). The electrochemical studies of the Ni@ NiOCN-4 nanocomposite reveal that it has a better electrochemical activity and ultralow onset potential with an E onset = 0.42 V Ag/AgCl and current density of 34 mA/cm 2 for a potential of 0.71 V Ag/AgCl toward urea oxidation reactions. The annealing temperature-dependent studies were found to be effective toward the morphology tunning and hence tunable catalytic performance toward urea oxidation reactions. In urea oxidation studies, chronoamperometry (i−t) and EIS analysis show that the proposed Ni@NiOCN-4 system has long-term stability and ultrafast electron transfer. This work showed a simple way for temperature-dependent morphology tuning of a catalyst with enhanced electrochemical activity for urea oxidation, which is useful for sustainable energy production utilizing urea-rich wastewater.

Critical Role of Interface Design in Acceleration of Overall Water Splitting and Hybrid Electrolysis Process: State of the Art and Perspectives

“…During the anodic potential sweep, the in situ converted metal oxyhydroxide, MOOH (M = Ni, Co, Mn), is the active species for the UOR. Ni based catalysts, like Ni MOF, 85 mesoporous Ni−P, 86 Ni 2 P, 87 NiO, 88,89 Ni@NiO nanoparticles, 90 alloyed Ni nanoparticles like Ni−Rh, 91 Ni−Co, 92 and Ni−Mn, 93 Ni sulfide, 94 Ni based bimetallic oxide/hydroxides such as NiMoO 4 , 95,96 NiCo 2 O 4 , 97 Ni 0.9 Fe 0.1 O x , 98 Cu:α-Ni(OH) 2 , 99 and NiMn−OH, 100 NiCo layered double hydroxide, 101 and Ni based heterostructures like NiCoP/MoS 2 , 102 were employed for the UOR. Zhang et al 81 reported NiMo nanotubes as a bifunctional catalyst (Figure 4A 82 for the overall urea assisted water splitting where only a cell voltage of 1.45 V is required to deliver a 20 mA cm −2 current density in 1 M KOH with 0.33 M urea as well as long-term cell stability for 20 h. DFT calculation predicted that the interface between Ni 3 S 2 and MoS 2 decreases the Gibbs free energy for the UOR.…”

“…During the anodic potential sweep, the in situ converted metal oxyhydroxide, MOOH (M = Ni, Co, Mn), is the active species for the UOR. Ni based catalysts, like Ni MOF, mesoporous Ni–P, Ni 2 P, NiO, , Ni@NiO nanoparticles, alloyed Ni nanoparticles like Ni–Rh, Ni–Co, and Ni–Mn, Ni sulfide, Ni based bimetallic oxide/hydroxides such as NiMoO 4 , , NiCo 2 O 4 , Ni 0.9 Fe 0.1 O x , Cu:α-Ni­(OH) 2 , and NiMn–OH, NiCo layered double hydroxide, and Ni based heterostructures like NiCoP/MoS 2 , were employed for the UOR. Zhang et al reported NiMo nanotubes as a bifunctional catalyst (Figure A–D) to catalyze the HER and UOR in alkaline electrolyte.…”

Spherical Ni/NiO nanoparticles decorated on nanoporous carbon (NNC) as an active electrode material for urea and water oxidation reactions

“…Herein, the urea molecules with electron-donating amino groups and electron-withdrawing carbonyl groups can be selectively adsorbed on NNC via. Ni/ NiOO-carbonyl group as an intermediate step, 5,[26][27][28][29] followed by the corresponding nucleophilic OH − attack. As a result, cleavage of the C-N bond became more favourable, and UOR could proceed at a lower potential.…”

“…To conrm CO 2 as the by-product, we performed the precipitation test using CaCO 3 aer the i-t stability test. 30 CaCO 3 reacts with dilute HCl, evolving CO 2 molecules and forms CaO (i.e., lime). CaO easily reacts with electrolyte solution and forms a white ppt of CaCO 3 .…”

Minireview of Coupled Electrochemical Hydrogen Production and Organic-Oxidation for Low Energy Consumption

“…Methanol is a typical alcohol, which can be electrochemically oxidized into CO 2 . Urea is a representative and simple amine, which can be oxidized to CO 2 and N 2 at the anode with H 2 forming at the cathode in a combined system. − In addition, some inorganic reactions can also be used as the institute of OER to combine with HER for energy effective H 2 production. NO is a typical harmful pollutant, which can be oxidized into nitrate in the combined systems with a potential of ∼1.07 V .…”