Electrocatalytic Oxidation Of Urea Research Articles

Coupling interface constructions of flower-like structure MoSe2–NiWSe2 for efficient oxygen evolution reaction and urea oxidation reaction

Because of its low thermodynamic voltage, the electrocatalytic urea oxidation reaction (UOR) is an effective way to replace the sluggish oxygen evolution reaction (OER) and address the issue of urea-rich water pollution. Herein, we have synthesized MoSe2–NiWSe2 with spherical nanoflower structure consisting of MoSe2 nanosheets and NiWSe2 nanosheets crisscrossed longitudinally and transversely. The results show that the prepared MoSe2–NiWSe2 has a significant competitive advantage in the UOR and OER. With 10 mA cm−2, a mere 200 mV overpotential was required, indicating high OER catalytic activity. MoSe2–NiWSe2-driven UOR might operate at a comparatively low potential of 1.36 V (10 mA cm−2). The overpotential did not significantly alter after 40 h of continuous operation, suggesting it possesses high UOR stability. A built-in electric field that aids in controlling the adsorption and oriented distribution of urea molecules and thus promotes the oxidative properties of water and urea forms at the interface of MoSe2 and NiWSe2, where the difference in electronegativity between the elements Mo and Ni induces self-driven charge transfer and interfacial coupling effects. This work offers a method for creating catalysts that produce more oxygen and clean up urea-rich water contamination.

Artificial Heterointerfaces with Regulated Charge Distribution of Ni Active Sites for Urea Oxidation Reaction.

In contrast to the thermodynamically unfavorable anodic oxygen evolution reaction, the electrocatalytic urea oxidation reaction (UOR) presents a more favorable thermodynamic potential. However, the practical application of UOR has been hindered by sluggish kinetics. In this study, hierarchical porous nanosheet arrays featuring abundant Ni-WO3 heterointerfaces on nickel foam (Ni-WO3/NF) is introduced as a monolith electrode, demonstrating exceptional activity and stability toward UOR. The Ni-WO3/NF catalyst exhibits unprecedentedly rapid UOR kinetics (200mAcm-2 at 1.384V vs. RHE) and a high turnover frequency (0.456s-1), surpassing most previously reported Ni-based catalysts, with negligible activity decay observed during a durability test lasting 150 h. Ex situ X-ray photoelectron spectroscopy and density functional theory calculations elucidate that the WO3 interface significantly modulates the local charge distribution of Ni species, facilitating the generation of Ni3+ with optimal affinity for interacting with urea molecules and CO2 intermediates at heterointerfaces during UOR. This mechanism accelerates the interfacial electrocatalytic kinetics. Additionally, in situ Fourier transform infrared spectroscopy provides deep insights into the substantial contribution of interfacial Ni-WO3 sites to UOR electrocatalysis, unraveling the underlying molecular-level mechanisms. Finally, the study explores the application of a direct urea fuel cell to inspire future practical implementations.

Engineering active sites on binary metal selenide heterointerface catalyst to boost urea electrooxidation

Electrocatalytic urea oxidation reaction (UOR) with a low thermodynamic potential is a perfect substitute for anodic oxygen evolution process (OER) in the effective generation of hydrogen. However, because of the slow kinetics of UOR, its potential application for commercial use remains untapped. Nickel-based materials may be an option for urea oxidation reaction but the heavily filled d orbital prevents enhanced adsorption and activity. Here, taking into account the adsorption-energy scaling limitations, Co3+ with partially filled d orbital is introduced into nickel selenide to form a heterointerface catalyst (2D CoSe2/Ni0.85Se) that enhances UOR. As anticipated, the 2D CoSe2/Ni0.85Se electrode displays a low potential of 1.33 V to achieve 100 mA cm−2 for UOR while retaining strong durability for 300 h. Further, 2D CoSe2/Ni0.85Se catalyst is used as an anode in an anion exchange membrane flow electrolyzer, which achieved an industrial-level voltage of 1.91 V at 1 A cm−2 and robust durability.

Water-Stable Pillared Three-Dimensional Zn-V Bimetal-Organic Framework for Promoted Electrocatalytic Urea Oxidation.

Urea oxidation reaction (UOR) is one of the potential routes in which urea-rich wastewater is used as a source of energy for hydrogen production. Metal-organic frameworks (MOFs) have promising applications in electrocatalytic processes, although there are still challenges in identifying the MOFs' molecular regulation and obtaining practical catalytic systems. The current study sought to synthesize [Zn6(IDC)4(OH)2(Hprz)2]n (Zn-MOF) with three symmetrically independent Zn(II) cations connected via linear N-donor piperazine (Hprz), rigid planar imidazole-4,5-dicarboxylate (IDC3-), and -OH ligands, revealing the 3,4T1 topology. The optimized noble-metal-free Zn0.33V0.66-MOF/NF electrocatalysts show higher robustness and performance compared to those of the parent Zn monometallic MOF/NF electrode and other bimetallic MOFs with different Zn-V molar ratios. The low potential of 1.42 V (vs RHE) at 50 mA cm-2 in 1.0 M KOH with 0.33 M urea required by the developed Zn0.33V0.66-MOF electrode makes its application in the UOR more feasible. The availability of more exposed active sites, ion diffusion path, and higher conductivity result from the distinctive configuration of the synthesized electrocatalyst, which is highly stable and capable of synergistic effects, consequently enhancing the desired reaction. The current research contributes to introducing a practical, cost-effective, and sustainable solution to decompose urea-rich wastewater and produce hydrogen.

Interfacial Coupling of NiPx/MoS2/CC Hybrid Catalysts for Effective Electrocatalytic Oxidation of Urea and Energy‐Saving Hydrogen Evolution

AbstractUrea oxidation reactions (UOR) coupled with hydrogen generation simultaneously is a promising strategy for developing sustainable energy conversion technologies, but the complexity of urea oxidation dynamics and the high coupling hydrogen evolution potential through a single catalyst limit its industrial application. Herein, a kind of novel bifunctional NiPx/MoS2/CC hybrid catalyst can be fabricated via a hydrothermal method followed by a facile in‐situ electrodeposition process. The prepared NiPx/MoS2/CC catalyst exhibits an overpotential of only 88 mV at 10 mA cm−2 for HER while the potential for UOR was only 1.36 V at 10 mA cm−2. Further, the urea electrolytic cell assembled of the NiPx/MoS2/CC catalyst displays low potential (1.45 V@10 mA cm−2) and better long‐term durability. The improved electrocatalytic performances are mainly attributed to the intimately coupled interface between NiPx and MoS2, enormously improving the conductivity and increasing the heterogenous interface active area. Additionally, the closely incorporated heterogeneous interfaces trigger charge redistribution, which induces the fast electron transfer from the NiPx to MoS2. In a word, the present results can provide a feasible research strategy for design advanced multi‐functional catalysts via interfacial engineering for clean energy conversion applications.

Construction of hierarchical CoNiMoOxHy/NF nanostructures for highly efficient urea oxidation reaction

Urea oxidation reaction (UOR) represents a promising alternative anodic reaction for saving the energy consumption of hydrogen production by water electrolysis, while its large-scale application is still hampered by UOR catalysts with unsatisfactory performance. Herein, a hierarchical self-standing CoNiMoOxHy/NF electrode is synthesized through a mild chemical etching and deposition process with ZIF-67 nanostructure grown on Ni foam as precursor. Electrocatalytic urea oxidation with CoNiMoOxHy/NF exhibits an outstanding activity with a quite low potential of 1.27 V (vs. RHE) at the benchmark current density of 10 mA cm−2. A low Tafel slope of 36 mV dec−1 indicates its superior reaction kinetics. By comparing with CoNiOxHy/NF, the enhanced activity is mainly attributed to the faster generation kinetics for active NiOOH species and more accessible active sites numbers. This work may provide a meaningful reference for design of high performance UOR catalysts.

Microwave-pulse synthesis of tunable 2D porous nickel-enriched LaMnxNi1−xO3 solid solution for efficient electrocatalytic urea oxidation

This work proposes a microwave-pulse method for rapidly synthesizing highly tunable 2D porous nickel-enriched LaMnxNi1−xO3 for a comprehensive understanding of UOR activity mechanisms.

Convenient synthesis and enhanced urea oxidation of NiO–CrO@N–C

The NiO–CrO@N–C composite, which was synthesized by amorphous NiO and CrO nanoparticles anchored on an N-containing carbon matrix, presents excellent activity and stability for the electrocatalytic oxidation of urea.

Microwave-assisted exploration of the electron configuration-dependent electrocatalytic urea oxidation activity of 2D porous NiCo2O4 spinel

Urea holds promise as an alternative water-oxidation substrate in electrolytic cells. High-valence nickel-based spinel, especially after heteroatom doping, excels in urea oxidation reactions (UOR). However, traditional spinel synthesis methods with prolonged high-temperature reactions lack kinetic precision, hindering the balance between controlled doping and highly active two-dimensional (2D) porous structures design. This significantly impedes the identification of electron configuration-dependent active sites in doped 2D nickel-based spinels. Herein, we present a microwave shock method for the preparation of 2D porous NiCo2O4 spinel. Utilizing the transient on-off property of microwave pulses for precise heteroatom doping and 2D porous structural design, non-metal doping (boron, phosphorus, and sulfur) with distinct extranuclear electron disparities serves as straightforward examples for investigation. Precise tuning of lattice parameter reveals the impact of covalent bond strength on NiCo2O4 structural stability. The introduced defect levels induce unpaired d-electrons in transition metals, enhancing the adsorption of electron-donating amino groups in urea molecules. Simultaneously, Bode plots confirm the impact mechanism of rapid electron migration caused by reduced band gaps on UOR activity. The prepared phosphorus-doped 2D porous NiCo2O4, with optimal electron configuration control, outperforms most reported spinels. This controlled modification strategy advances understanding theoretical structure-activity mechanisms of high-performance 2D spinels in UOR.

Highly stable urea oxidation electrolysis via Rh nanoparticles residing in the porous LaNiO3 nanocubes

Electrocatalytic urea oxidation reaction (UOR) is recognized as an effective approach for the degradation of urea in wastewater into harmless N2 and CO2 due to its low-energy anode reaction. However, there remains a pressing need for an efficient electrocatalyst to enhance the activity and stability of electrolytic urea. In this study, we employed the hydrothermal technique followed by a reduction-impregnation treatment to load the precious metal Rh on the porous LaNiO3 nanocubes. The Rh/LaNiO3-400 °C nanocubes prepared by this method not only retained the porous structure of the LaNiO3 nanocubes but also enhanced the catalytic properties of the precious metal. The synergistic effect between these Rh and LaNiO3 significantly boosted the efficiency of the electrolytic urea process. Characterization tests confirmed that Rh nanoparticles were successfully loaded into the porous LaNiO3 nanocubes, facilitating better interaction between the catalyst and the electrolyte. Electrochemical tests demonstrated that the stability of Rh/LaNiO3-400 °C for up to 72 h. This remarkable stability suggests that such a robust electrocatalyst has the potential to serve as a cornerstone for efficient and long-lasting hydrogen production.

NiS–NiS2 heterostructure for efficient electrocatalytic overall urea splitting

Heterogeneous catalysts possess many advantages over single-phase catalysts. However, how to tune the heterogeneous interface state and density in heterostructures to optimize their electrocatalytic performance is still a challenge. Here, we propose a method for the preparation of NiS–NiS2 heterostructure by vulcanization of nickel foam at high temperature, which can effectively tune the weight ratio of NiS to NiS2 in heterostructure and their corresponding electrocatalytic urea oxidation reaction (UOR), hydrogen evolution reaction (HER) and overall urea splitting performance. The electrocatalytic activity show a trend of volcano curve with the increase of the ratio of NiS to NiS2, and the best electrocatalytic activity was obtained at the ratio of 6.74, in which the potentials at current density of 10 mA cm−2 of UOR, HER and overall urea splitting are 1.28 V, −49.5 mV and 1.34 V versus reversible hydrogen electrode (vs. RHE), and the Tafel slopes are 21.7, 74.1 and 90.9 mV dec−1, respectively. Furthermore, it also demonstrates excellent electrocatalytic stability. This work provides an effective way to tune the interfacial structure of heterogeneous electrocatalysts while significantly improving their electrocatalytic performance, which is beneficial to the development of efficient heterostructure and expand their applications.

Boosted urea electro-oxidation over Ni3N-based nanocomposite via systematic regulation tactic

Exploiting high-efficiency Ni-based materials for electrocatalytic urea oxidation reaction (UOR) is critical for urea-related technologies. The catalytic site density, intrinsic activity, charge transfer, and mass diffusion determine overall electrocatalytic efficiency. Simultaneous modulation over the above four factors promises advanced electrocatalysis, yet challenging. Herein we propose a systematic regulation tactic over composition and geometric structure, constructing a nanocomposite comprising Mn doped Ni3N nanoparticles anchored on reduced graphene oxide (rGO/Mn-Ni3N), achieving elegant integration of four design principles into one, thereby eminently boosting UOR. Particularly, Mn doping in Ni3N can modulate electronic state to induce intrinsic activity regulation. Combining metallic Mn-Ni3N with rGO to engineer hierarchical architecture not only promotes charge transfer, but also enriches active site population. Intriguingly, improved hydrophilicity could impart better electrolyte penetration and gas escape. Consequently, such system-optimized rGO/Mn-Ni3N demonstrates state-of-the-art-level UOR electrocatalysis. This work offers a novel paradigm to create advanced catalysts via systematic and integrated modulation.

Collaborative optimization of thermodynamic and kinetic for Ni-based hydroxides in electrocatalytic urea oxidation reaction

Ni-based hydroxides are brilliant electrocatalysts for alkaline urea oxidation reaction (UOR). Herein, multiple Ni-based hydroxides were investigated by electrocatalytic test for UOR performance. Electrocatalytic performance of different ratios of NiCo LDHs was further determined to exploring electrochemical reaction pathway and thermodynamic mechanism. Results indicate appropriate Co element doping content in Ni hydroxide could greatly improve UOR performance. Results of XPS and in situ Raman indicate only part of NiCo hydroxides were converted to NiCo oxyhydroxides which drive the subsequent UOR. Moreover, electrocatalytic UOR on NiCo oxyhydroxides is found in competition with redox of NiCo hydroxides. Density function theory (DFT) calculation manifests that the energy barrier of UOR on NiCo oxyhydroxides is lower than redox of NiCo hydroxides which become the limitation reaction. Energy barrier gap between UOR and redox which provide driving force for UOR which is the primary cause of fast kinetic.

Cobalt hydroxide supported nickel nanoparticles for an efficient electrocatalytic urea oxidation reaction

An efficient electrochemical urea oxidation reaction (UOR) could be used in energy production technology. Metallic nickel nano-particles (Ni NPs) are incorporated in cobalt hydroxide layered material to form Ni/Co(OH)2. The synthesized material is utilized as an electrocatalyst in UOR. It has been revealed that the incorporation of Ni NPs into cobalt hydroxide significantly enhances their electrocatalytic activity toward UOR. Ni/Co(OH)2 catalyzes UOR at a very low anodic potential of 1.15 V vs RHE with a peak current density of 14.2 mAcm−2 and Tafel slope of 75 mVdec−1. The current work is a step ahead towards use of transition metal hydroxide (TMH) as support in the electrocatalytic oxidation applications especially UOR.

Study on the electrocatalytic oxidation of urea at nickel/iron deposited electrodes

Nickel and nickel-iron modified glass carbon electrodes were prepared by electrodeposition in 20 mmol/LNiSO4 and 5 mmol/LFeSO4 + 20 mmol/LNiSO4 solution. The electrocatalytic oxidation of urea at two modified electrodes under alkaline conditions were investigated. In 1 mol/L NaOH solution, the nickel modified electrode showed better results than nickel-iron modified electrode for the electrocatalytic oxidation of urea. The effects of different urea concentrations, different NaOH concentrations, and different scan rates on the electrocatalytic properties of the two modified electrodes were investigated.

Quenching-assisted surface functionalization of metal oxide for highly enhanced electrocatalytic urea oxidation

Urea oxidation reaction (UOR) is considered as a good substitute for oxygen evolution reaction (OER) because of its low theoretical onset potential. Surface modification is an effective strategy to tune the catalytic activity of the catalysts towards UOR. Here, we developed a facile and universal quenching strategy to prepare sulfate-modified NiO nanosheets (NiO@NF-20S). Compared with the pristine NiO nanosheets, the electrocatalytic performance of the NiO@NF-20S is greatly improved, showing a small potential of 1.40 V vs. RHE to deliver a current density of 200 mA cm−2 as well as robust electrochemical stability. The outstanding electrocatalytic performance of the NiO@NF-20S is mainly ascribed to the improved surface wettability and the promoted Ni2+/Ni3+ redox reaction. The quenching strategy can be expanded to not only various kinds of functional groups from nitric acid and phosphoric acid but also other metal oxides such as NiCoOx and NiCrOx. This work provides a new avenue to the design of surface-functionalized metal oxide catalysts for electrocatalysis.

Exploring the role of different morphologies of β–Ni(OH)2 for electrocatalytic urea oxidation and the effects of electrochemically active surface area

Ni(OH)2, as a multifunctional material, has found its applications in a great number of research areas. In particular, it is an efficient catalyst for urea oxidation reaction (UOR), which is an important alternative to oxygen evolution reaction in electrocatalytic water splitting. This work investigates the effect of materials morphology on the electrocatalytic UOR performance of β–Ni(OH)2, as well as the importance of characterising the catalysts’ surface by electrochemical active surface area. Three different morphologies (nanoflowers, nanocubes, and nanosheets) were prepared via a simple hydrothermal approach. The morphology and structure of the as-prepared samples were carefully examined by scanning electron microscopy, transmission electron microscopy, and powder X-ray diffraction.The UOR performance of β–Ni(OH)2was evaluated by means of cyclic voltammetry, linear sweep voltammetry, Tafel analysis, and electrochemical surface area. Nanosheet Ni(OH)2 electrocatalyst exhibits higher current density responses (28.3 mA cm−2ECSA at 1.6 V vs. RHE) and a lower slope in the Tafel plot (72.6 mV dec-1). Consequently, due to the exposure of more active sites to the reactants, the Ni(OH)2 electrode with nanosheet morphology displayed higher electrocatalytic performance during UOR compared to the nanoflower and nanocube samples.

Bimetallic MoO3/Ni-N-C Nanoalloys Derived from MOFs for Electrocatalytic Urea Oxidation Reaction

In electrochemical energy storage and conversion systems, urea oxidation reaction (UOR) can produce hydrogen and mitigate pollution from urea-rich wastewater in a low-energy manner, whereas the development of this technique was limited via a lack of economical and cost-effective UOR catalysts. Herein, a unique electrocatalyst of MoO3/Ni-N-C was synthesized from a Mo element-incorporated Ni-MOF by heating under an inert atmosphere. The prepared MoO3/Ni-N-C electrode shows superior activity toward UOR, which only needs a low potential of 1.42 V (vs RHE) at 50 mA cm–2 in 1.0 M KOH with 0.5 M urea. The excellent performance for UOR is attributed to the synergistic effect between molybdenum and nickel, the modulation of the electronic structure for the nickel site by MoO3, accelerating the charge transfer, and tuning the reaction interface adsorption energy to enhance electrocatalytic activity. This work provides strategies and directions for exploring other advanced UOR electrode material designs.

Exploring The Synergistic Effect Of CoSeP/CoP Interface Catalyst For Efficient Urea Electrolysis.

Electrocatalytic oxidation of urea (UOR) is a potential energy-saving hydrogen production technology that can replace oxygen evolution reaction (OER). Therefore, CoSeP/CoP interface catalyst is synthesized on nickel foam using hydrothermal, solvothermal, and in situ template methods. The strong interaction of tailored CoSeP/CoP interface promotes the hydrogen production performance of electrolytic urea. During the hydrogen evolution reaction (HER), the overpotential can reach 33.7mV at 10mA cm-2 . The cell voltage can reach 1.36V at 10mA cm-2 in the overall urea electrolytic process. Notably, the overall urine electrolysis performance of the catalyst in the human urine medium can reach 1.40V at 10mA cm-2 and can exhibit durable cycle stability at 100mA cm-2 . Density functional theory (DFT) proves that the CoSeP/CoP interface catalyst can better adsorb and stabilize reaction intermediates CO* and NH* on its surface through a strong synergistic effect, thus enhancing the catalytic activity.

Key Roles of Interfacial OH- ion Distribution on Proton Coupled Electron Transfer Kinetics Toward Urea Oxidation Reaction.

Enhancing alkaline urea oxidation reaction (UOR) activity is essential to upgrade renewable electrolysis systems. As a core step of UOR, proton-coupled electron transfer (PCET) determines the overall performance, and accelerating its kinetic remains a challenge. In this work, a newly raised electrocatalyst of NiCoMoCuOx Hy with derived multi-metal co-doping (oxy)hydroxide species during electrochemical oxidation states is reported, which ensures considerable alkaline UOR activity (10/500mA cm-2 at 1.32/1.52V vs RHE, respectively). Impressively, comprehensive studies elucidate the correlation between the electrode-electrolyte interfacial microenvironment and the electrocatalytic urea oxidation behavior. Specifically, NiCoMoCuOx Hy featured with dendritic nanostructure creates a strengthened electric field distribution. This structural factor prompts the local OH- enrichment in electrical double layer (EDL), so that the dehydrogenative oxidation of the catalyst is directly reinforced to facilitate the subsequent PCET kinetics of nucleophilic urea, resulting in high UOR performance. In practical utilization, NiCoMoCuOx Hy -driven UOR coupled cathodic hydrogen evolution reaction (HER) and carbon dioxide reduction reaction (CO2 RR), and harvested high value-added products of H2 and C2 H4 , respectively. This work clarifies a novel mechanism to improve electrocatalytic UOR performance through structure-induced interfacial microenvironment modulation.