Electrocatalytic Oxidation Of Urea Research Articles

H2O2 treatment boosts activity of NiFe layered double hydroxide for electro-catalytic oxidation of urea

Urea oxidation reaction (UOR) provides a method for hydrogen production besides wastewater treatment, but the current limited catalytic activity has prevented the application. Herein, we develop a novel H2O2 treatment strategy for tailoring the surface oxygen ligand of NiFe-layered double hydroxides (NiFe-LDH). The sample after H2O2 treatment (NiFeO-LDH) shows significant enhancement on UOR efficiency, with the potential of 1.37 V (RHE) to reach a current density of 10 mA/cm2. The boost is attributed to the richness adsorption O ligand on NiFeO-LDH as revealed by XPS and Raman analysis. DFT calculation indicates formation of two possible types of oxygen ligands: adsorbed oxygen on the surface and exposed from hydroxyl group, lowered the desorption energy of CO2 product, which lead to the lowered onset potential. This strategy is further extended to NiFe-LDH nano sheet on Ni foam to reach a higher current density of 440 mA/cm2 of UOR at 1.8 V (RHE). The facile surface O ligand manipulation is also expected to give chance to many other electro-catalytic oxidations.

MoS2/Ni3S2 Schottky heterojunction regulating local charge distribution for efficient urea oxidation and hydrogen evolution

Electrocatalytic urea oxidation reaction (UOR) is a prospective method to substitute the slow oxygen evolution reaction (OER) and solve the problem of urea-rich water pollution due to the low thermodynamic voltage, but its complex six-electron oxidation process greatly impedes the overall efficiency of electrolysis. Here, density functional theory (DFT) calculations imply that the metallic Ni3S2 and semiconductive MoS2 could form Mott-Schottky catalyst because of the suitable band structure. Therefore, we synthesized MoS2/Ni3S2 electrocatalyst by a simple hydrothermal method, and studied its UOR and hydrogen evolution reaction (HER) performance. The formed MoS2/Ni3S2 Schottky heterojunction is only required 109 and 166 mV to obtain ±10 mA cm−2 for UOR and HER, respectively, showing great bifunctional catalytic activity. Moreover, the full urea electrolysis driven by MoS2/Ni3S2 delivers 10 and 100 mA cm−2 at a relatively low potential of 1.44 and 1.59 V. Comprehensive experiments and DFT calculations demonstrate that the MoS2/Ni3S2 Schottky heterojunction causes self-driven charge transfer at the interface and forms built-in electric field, which is not only benefit to reduce H* adsorption energy, but also helps to adjust the absorption and directional distribution of urea molecules, thereby promoting the activity of decomposition of water and urea. This research furnishes a tactic to devise more efficient catalysts for H2 generation and the treatment of urea-rich water pollution.

Novel peapod-like Ni2P@N-doped carbon nanorods array on carbon fiber for efficient electrocatalytic urea oxidation and hydrogen evolution reaction

Designing and optimizing structure is an effective method to enhance electrocatalytic performance of transition metal-based catalysts. In this work, an innovative nanostructured electrode, consisted of peapod-like Ni2P@N-doped carbon nanorods array coating on carbon fiber (CF@p-Ni2P@NC), is devised and synthesized. The N-doped carbon layer is crucial for maintaining the peapod-like nanostructure, which allows for multi-channel electrolyte transport and gas product release. And the carbon layer coating Ni2P nanoparticles also enhance electrical conductivity and stability, thus ensuring fast electron transport from/to active sites and the long-term stability of catalyst during urea oxidation reaction (UOR)/hydrogen evolution reaction (HER). Benefit from the reasonable structure, CF@p-Ni2P@NC present perfect performance with getting 100 mA cm−2 at potential/overpotential of 1.417/0.194 V for UOR/HER in 1.0 M KOH containing 0.5 M urea. In addition, the overall urea-electrolysis system using CF@p-Ni2P@NC bifunctional electrode only requires 1.590 V to obtain 100 mA cm−2.

One-step synthesis of NiS2/rGO composite for efficient electrocatalytic urea oxidation

One-step synthesis of NiS2/rGO composite for efficient electrocatalytic urea oxidation

Interfacial engineering of an FeOOH@Co3O4 heterojunction for efficient overall water splitting and electrocatalytic urea oxidation

Constructing heterostructure is an efficient method to provide more active sites and optimize electronic structure for improving the oxygen evolution reaction (OER) and urea oxidation reaction (UOR) performance. Herein, the 3D FeOOH@Co3O4 heterostructure was constructed using FeOOH layer (10–20 nm) coated on the surface of Co3O4 nanoneedles through the strong hydrolysis of Fe3+. The FeOOH@Co3O4 heterostructure not only retains the nanoneedle structure with open frameworks, but also improves the specific surface area and expedites the charge transfer. The FeOOH@Co3O4-240 heterostructure affords a remarkable OER performance with low overpotential of 228 mV at 10 mA·cm−2 in 1 M KOH solution. The symmetrical urea electrolyzer using FeOOH@Co3O4-240 as both anode and cathode delivers 10 mA/cm2 at 1.43 V. Density functional theory (DFT) calculations unveil that the FeOOH@Co3O4-240 heterostructure could adjust the electronic structure and strengthen the conductivity. This work offered a facile strategy for designing heterojunction catalysts in an economic way.

Ultrathin two-dimensional nickel-organic framework nanosheets for efficient electrocatalytic urea oxidation

Synthesis of highly-efficiency electrocatalysts with controllable morphology, enriched active sites, and low cost is of great significance for urea oxidation reaction (UOR) applications. In this work, novel two-dimensional (2D) nickel-based metal-organic framework (Ni-MOF) nanosheets comprising Ni2+ and an organic ligand of 4-Dimethylaminopyridine (Ni-DMAP-t, where t is the synthesis time) are firstly synthesized by a facile one-pot solvothermal method. By thickness regulation of Ni-DMAP-t nanosheets, the self-supported Ni-DMAP-2 with the smallest thickness on Ni foam (Ni-DMAP-2/NF) exhibits high electrocatalytic activity toward UOR with a low potential of 1.45 V at a current density of 100 mA cm−2. Moreover, by further coupling with the cathodic hydrogen evolution reaction, the urea-assisted electrolytic hydrogen production system using Ni-DMAP-2/NF as anode displays a dramatic voltage reduction by 290 mV at a current density of 50 mA cm−2 as compared with that of conventional water electrolysis using the same electrodes. Such a superior UOR electrocatalytic activity of Ni-DMAP-2/NF is ascribed to the abundant Ni active sites exposed on the surface of Ni-DMAP-2, as well as the accelerated electron/ion transfer properties endowed by its ultrathin 2D nanosheets structure. This work offers some new ideas into the design and development of ultrathin 2D Ni-based MOF electrocatalysts for urea-related energy storage devices.

Optimizing local charge distribution of metal nodes in bimetallic metal–organic frameworks for efficient urea oxidation reaction

A significantly lower voltage was required in NiFe-MIL-53-NH 2 when using full urea electrolysis instead of overall water splitting. • Incorporating Fe induces the formation of electrophilic Ni 3+ and nucleophilic Fe 3+ . • The bimetallic NiFe-MIL-53-NH 2 presents excellent electrocatalytic UOR activity. • This work provides a new strategy to explore effective UOR electrocatalysts. Electrocatalytic urea oxidation reaction (UOR) presents lower thermodynamic potential than oxygen evolution reaction (OER), thus exhibiting promising potential to enhance the efficiency of overall water splitting. However, due to the intrinsically sluggish six-electron transfer process, the efficiency of UOR is still not satisfied. In response, we synthesized a bimetallic NiFe-MIL-53-NH 2 with superior activity toward UOR, which only needs a low potential of 1.398 V vs. RHE to obtain 50 mA cm −2 in 1.0 M KOH with 0.33 M urea, much lower than that in 1.0 M KOH (1.721 V vs. RHE). Furthermore, NiFe-MIL-53-NH 2 presents significantly more excellent UOR activity compared to its monometallic counterparts. The TOF value in NiFe-MIL-53-NH 2 (0.16 s −1 ) at 1.4 V vs. RHE is about 133- and 246-folds higher than that Ni-MIL-53-NH 2 (1.2 × 10 -3 s −1 ) and Fe-MIL-53-NH 2 (6.5 × 10 -4 s −1 ), respectively. XPS characterization discloses that the incorporation of Fe into Ni-MIL-53-NH 2 framework optimizes the local charge distribution of metal nodes, leading to the formation of electrophilic Ni 3+ and nucleophilic Fe 3+ species, which can absorb electron-donating –NH 2 and electron-withdrawing C = O groups in urea, respectively, and therefore result in excellent UOR. This simple strategy of regulating local charge distribution of active species by fabricating bimetallic MOFs provides a new strategy and direction to explore other highly efficient UOR electrocatalysts.

Dynamic active sites on plasma engraved Ni hydroxide for enhanced electro-catalytic urea oxidation

The urea oxidization reaction (UOR) is an important anodic reaction in electro-catalytic energy conversion. However, the sluggish reaction kinetics and complex catalyst transformation in electrocatalysis require activity improvement and better mechanistic understanding of the state-of-the-art Ni(OH)2 catalyst. Herein, by utilizing low-temperature argon (Ar) plasma processing, tooth-wheel Ni(OH)2 nanosheets self-supported on Ni foam (Ni(OH)2-Ar) are demonstrated to have improved UOR activity compared to conventional Ni(OH)2. The theoretical assessment confirms that the edge has a smaller cation vacancy formation energy than the basal plane, consequently explaining the structural formation. Operando and quasi-operando methods are employed to investigate the dynamic evolution of the Ni(OH)2 film in UOR. The crucial dehydrogenation products of Ni(OH)5O- intermediates are identified to be stable on the etched edge and explain the enhanced UOR in the low potential region. In addition, the dynamic active sites are monitored to elucidate the reaction mechanism in different potential ranges.

Phase and crystallinity regulations of Ni(OH)2 by vanadium doping boost electrocatalytic urea oxidation reaction

Direct urea fuel cell (DUFC) and overall urea splitting system have attracted considerable attention as promising choice for energy conversion. Whereas, the anodic half reaction of electrocatalytic urea oxidation reaction (UOR) in these systems awfully limited their practical application due to the complex 6-electron transfer process. Herein, vanadium doped nickel (V-Ni(OH)2) with highly efficient electrocatalytic activity toward UOR was developed by a simple coprecipitation method. The introducing of V not only promotes the phase transforming from inactive β-Ni(OH)2 to highly active α-Ni(OH)2, but also simultaneously modulates the electron environment of Ni, facilitating high valence species Ni3+ generation in low overpotential, enhancing the electrocatalytic activity potent of each Ni3+ site and speeding up the electrocatalytic reaction. The optimal V-Ni(OH)2 catalyst exhibits a summit current density of 241 mA cm−2 at 1.6 V vs. RHE, a Tafel slope of 32.15 mV dec-1, outperforming β-Ni(OH)2 and most catalysts that tested on glassy carbon electrode. Furthermore, the assembled direct urea hydrogen peroxide fuel cell (DUPFC) offers a maximum power density of 13.4 mW cm−2 at 20 °C. This work provides an example of combing phase-regulation and electron modulation method for effective UOR electrocatalysts design.

Nickel sulphide decorated nitrogen rich ordered mesoporous carbon (NOMC) as an efficient catalyst for the electrocatalytic oxidation of urea in alkaline medium

The urea oxidation reaction (UOR), as a feasible alternative for the slow oxygen evolution reaction (OER), is recognized as an encouraging puissant approach for hydrogen generation through water splitting. The route also offers excellent potential for hydrogen production through wastewater remediation. Here, a simple synthetic strategy has been adopted to embed NiS in a nitrogen-rich stable and activated mesoporous carbon matrix (NOMC) that has been successfully exploited for UOR. The NOMC supported nickel sulfide catalyst with high electrochemically active surface area (ECSA) exhibits a very good response towards the electro-catalytic oxidation of urea in an alkaline medium with a low working oxidation potential (potential corresponding to the current density value of 10 mA/cm2 taken as a standard) of 1.34 V (vs. RHE). The introduction of heteroatom (N) to the mesoporous carbon support and subsequent incorporation of metal sulfide rather than metal oxide or metal hydroxide, as reported previously, is done purposefully to increase the electrocatalytic activity of the catalyst through the synergistic effects of charge density with carbon support. The synergism is further supported by the comparative response in urea oxidation reaction (UOR) for NiS/NOMC catalyst compared to other Ni-based catalysts like Ni(OH)2, NiS, and NiS/CMK-3, which indicates that the activity is highest for NiS/NOMC. The catalyst attains good stability in an alkaline medium. The mesoporous carbon framework (NOMC) with considerably high BET surface area, large pore volume, and interconnected ion diffusion channels accelerate the transport of electrons through the porous surface, which makes NiS/NOMC highly efficient and stable as an electrocatalyst for the oxidation of urea in comparison to its other composite catalysts in alkaline medium.

Nickel Nanocrystals Anchored Nitrogen-Doped Carbon Derived from Eggshell Membrane as an Efficient Catalyst for the Electrocatalytic Oxidation of Urea

Nickel Nanocrystals Anchored Nitrogen-Doped Carbon Derived from Eggshell Membrane as an Efficient Catalyst for the Electrocatalytic Oxidation of Urea

H2o2 Treatment Boosts Activity of Nife Layered Double Hydroxide for Electro-Catalytic Oxidation of Urea

H2o2 Treatment Boosts Activity of Nife Layered Double Hydroxide for Electro-Catalytic Oxidation of Urea

H2o2 Treatment Boosts Activity of Nife Layered Double Hydroxide for Electro-Catalytic Oxidation of Urea

H2o2 Treatment Boosts Activity of Nife Layered Double Hydroxide for Electro-Catalytic Oxidation of Urea

Recent advances in the pre-oxidation process in electrocatalytic urea oxidation reactions.

The electrocatalytic urea oxidation reaction (UOR) has attracted substantial research interests over the past few years owing to its critical role in coupled electrochemical systems for energy conversion, for example, coupling with the hydrogen evolution reaction (HER) to realize urea-assisted hydrogen production and assembling direct urea fuel cells (DUFC) by coupling with the oxygen reduction reaction (ORR). The UOR process has been proved to be a two-step process which involves an electrochemical pre-oxidation reaction of the metal sites and a subsequent chemical oxidation of the urea molecules on the as-formed high-valence metal sites. Hence, designing advanced (pre-)catalysts with a boosted pre-oxidation reaction is of great importance in improving the UOR performance and thus accelerating the coupled reactions. In this feature article, we discuss the significant role of the pre-oxidation process during the urea electro-oxidation reaction, and summarize detailed strategies and recent advances in promoting the pre-oxidation reaction, including the modulation of the crystallinity, active phase engineering, defect engineering, elemental incorporation and constructing hierarchical nanostructures. We anticipate that this feature article will offer helpful guidance for the design and optimization of advanced (pre-)catalysts for UOR and related energy conversion applications.

CeO2 modified Ni-MOF as an efficient catalyst for electrocatalytic urea oxidation

The development of cost-efficient electrocatalysts for urea oxidation reaction (UOR) is a challenge due to the slow kinetics. In this work, we demonstrated a one-pot hydrothermal synthetic method to fabricate CeO2 modified Ni-MOF nanosheets. When evaluted as UOR catalysts, the 3% CeO2/Ni-MOF possesses outstanding catalytic activity, achieving a current density of 10 mA cm−2 at a low potential of 1.356 V with a small Tafel slope of 13.83 mV dec−1. It is considered that the unique interactions between CeO2 nanoparticles (NPs) and Ni-MOF nanosheets (NSs) play the significant role in the enhancement of the catalytic performance by inducing the formation of abundant defects and optimized surface states.

Metal-Organic Frameworks Offering Tunable Binary Active Sites toward Highly Efficient Urea Oxidation Electrolysis.

Electrocatalytic urea oxidation reaction (UOR) is regarded as an effective yet challenging approach for the degradation of urea in wastewater into harmless N2 and CO2. To overcome the sluggish kinetics, catalytically active sites should be rationally designed to maneuver the multiple key steps of intermediate adsorption and desorption. Herein, we demonstrate that metal-organic frameworks (MOFs) can provide an ideal platform for tailoring binary active sites to facilitate the rate-determining steps, achieving remarkable electrocatalytic activity toward UOR. Specifically, the MOF (namely, NiMn0.14-BDC) based on Ni/Mn sites and terephthalic acid (BDC) ligands exhibits a low voltage of 1.317 V to deliver a current density of 10 mA cm−2. As a result, a high turnover frequency (TOF) of 0.15 s−1 is achieved at a voltage of 1.4 V, which enables a urea degradation rate of 81.87% in 0.33 M urea solution. The combination of experimental characterization with theoretical calculation reveals that the Ni and Mn sites play synergistic roles in maneuvering the evolution of urea molecules and key reaction intermediates during the UOR, while the binary Ni/Mn sites in MOF offer the tunability for electronic structure and d-band center impacting on the intermediate evolution. This work provides important insights into active site design by leveraging MOF platform and represents a solid step toward highly efficient UOR with MOF-based electrocatalysts.

Hierarchical Ni-Mo-P nanoarrays toward efficient urea oxidation reaction.

The urea oxidation reaction (UOR), which possesses a low theoretical potential and superior kinetics, is an attractive substitute for the anodic oxygen evolution reaction (OER) in overall water splitting; however, the implementation of hydrogen production in overall urea splitting is impeded by the deficiency of highly efficient, durable and cost-effective catalysts. Herein, we fabricated an Ni2P-MoP2 heterostructure with a hierarchical structure grown on carbon paper (Ni-Mo-P/CP), which exhibited robust activity and outstanding durability for the electrocatalytic oxidation of urea. The Ni-Mo-P/CP catalyst possessed an ultralow potential of 1.39 V to obtain the current density of 100 mA cm-2, small Tafel slope (27 mV dec-1) and long-term durability with almost no decay within 15 h. The experimental characterization revealed that the optimized electronic structure and the synergistic effect of abundant exposed active sites in the Ni-Mo-P/CP catalyst contribute to the efficient UOR catalytic activity. This work enriches the candidate catalysts for the UOR and promotes the industrial development of hydrogen production.

Regulating the pyrolysis process of cation intercalated MnO2 nanomaterials for electrocatalytic urea oxidation performance.

Exploring an efficient way to enhance electron/ion transport behavior of nanomaterials plays an important role in the study of energy storage & conversion. However, the evolution rules of lattice and electronic structure during the pyrolysis process of low-dimensional nanomaterials, which further regulate its electron/ion transport properties, have not been effectively elucidated. Here we study the pyrolysis process of cation intercalated MnO2 as a case for realizing optimized electron/ion transport behavior. In our case, thermogravimetry-mass spectrometry (TG-MS) was adopted for tracking the remaining products in pyrolysis and decomposition products, further finding out the evolution law of the manganese-oxygen polyhedron structure during the pyrolysis. Moreover, the internal relations between the crystal structure and the electronic structure during the pyrolysis process of low-dimensional manganese oxide are revealed by fine structure characterization. As expected, partially treated 2D MnO2 nanosheets with controlled pyrolysis displays ultrahigh UOR performance with the overpotential of 1.320 V vs. RHE at the current density of 10 mA cm-2, which is the best value among non-nickel-based materials. We anticipate that studying the mechanism of the pyrolysis process has important guiding significance for the development of high electron/ion transport devices.

Interface enables faster surface reconstruction in a heterostructured Co–Ni–S electrocatalyst towards efficient urea oxidation

The electrocatalytic urea oxidation reaction (UOR) can be utilized as an alternative anodic reaction for water electrolysis to provide more economic electrons and high-efficiency H2 production.

Synergistic doping and structural engineering over dendritic NiMoCu electrocatalyst enabling highly efficient hydrogen production.

The development of non-precious metal electrocatalysts with remarkable activity is a major objective for achieving high-efficiency hydrogen generation. Here, a trimetallic electrocatalyst with a dendritic nanostructure, which is denoted as NiMoCu-NF, was fabricated on nickel foam via a gas-template electrodeposition strategy. By virtue of the metallic doping and structural optimization, NiMoCu-NF exhibits superior HER electrocatalytic activity with an overpotential of 52 mV at 10 mA cm-2. Additionally, the NiMoCu-NF-derived nickel-based (oxy)hydroxide species in the oxidation operating state deliver considerable electrocatalytic urea oxidation reaction (UOR) performance to match the efficient H2 generation, with a low voltage of 1.54 V to realize overall electrolysis at 50 mA cm-2. Impressively, combined experimental and simulation analysis demonstrate that the NiMoCu-NF with a favorable 3D nanostructure feature effectively regulates the heterogeneous interface states, inducing a "Gas Microfluidic Pumping" (GMP) effect that improved electron-mass transfer properties to accelerate the electrocatalytic reaction kinetics of either the HER or UOR.