Showing papers on "Urea published in 2022"

A review of Ni based powder catalyst for urea oxidation in assisting water splitting reaction

Abstract: Water splitting has been regarded as a sustainable and environmentally-friendly technique to realize green hydrogen generation, while more energy is consumed due to the high overpotentials required for the anode oxygen evolution reaction. Urea electrooxidation, an ideal substitute, is thus received increasing attention in assisting water-splitting reactions. Note that highly efficient catalysts are still required to drive urea oxidation, and the facile generation of high valence state species is significant in the reaction based on the electrochemical-chemical mechanisms. The high cost and rareness make the noble metal catalysts impossible for further consideration in large-scale application. Ni-based catalysts are very promising due to their cheap price, facile structure tuning, good compatibility, and easy active phase formation. In the light of the significant advances made recently, herein, we reviewed the recent advances of Ni-based powder catalysts for urea oxidation in assisting water-splitting reaction. The fundamental of urea oxidation is firstly presented to clarify the mechanism of urea-assisted water splitting, and then the prevailing evaluation indicators are briefly expressed based on the electrochemical measurements. The catalyst design principle including synergistic effect, electronic effect, defect construction and surface reconstruction as well as the main fabrication approaches are presented and the advances of various Ni-based powder catalysts for urea assisted water splitting are summarized and discussed. The problems and challenges are also concluded for the Ni-based powder catalysts fabrication, the performance evaluation, and their application. Considering the key influencing factors for catalytic process and their application, attention should be given to structure−property relationship deciphering, novel Ni-based powder catalysts development and their construction in the real device; specifically, the effort should be directed to the Ni-based powder catalyst with multi-functions to simultaneously promote the fundamental steps and high anti-corrosion ability by revealing the local structure reconstruction as well as the integration in the practical application. We believe the current summarization will be instructive and helpful for the Ni-based powder catalysts development and understanding their catalytic action for urea-assisted hydrogen generation via water splitting technique. Advances and challenges of Ni based powder catalyst were reviewed for urea oxidation in assisting water-splitting reaction.

Oxygen Vacancy-Mediated Selective C-N Coupling toward Electrocatalytic Urea Synthesis.

Abstract: The electrocatalytic C-N coupling for one-step urea synthesis under ambient conditions serves as the promising alternative to the traditional urea synthetic protocol. However, the hydrogenation of intermediate species hinders the efficient urea synthesis. Herein, the oxygen vacancy-enriched CeO2 was demonstrated as the efficient electrocatalyst with the stabilization of the crucial intermediate of *NO via inserting into vacant sites, which is conducive to the subsequent C-N coupling process rather than protonation, whereas the poor selectivity of C-N coupling with protonation was observed on the vacancy-deficient catalyst. The oxygen vacancy-mediated selective C-N coupling was distinguished and validated by the in situ sum frequency generation spectroscopy. The introduction of oxygen vacancies tailors the common catalyst carrier into an efficient electrocatalyst with a high urea yield rate of 943.6 mg h-1 g-1, superior than that of partial noble-metal-based electrocatalysts. This work provides novel insights into the catalyst design and developments of coupling systems.

A Defect Engineered Electrocatalyst that Promotes High-Efficiency Urea Synthesis under Ambient Conditions.

Abstract: Synthesizing urea from nitrate and carbon dioxide through an electrocatalysis approach under ambient conditions is extraordinarily sustainable. However, this approach still lacks electrocatalysts developed with high catalytic efficiencies, which is a key challenge. Here, we report the high-efficiency electrocatalytic synthesis of urea using indium oxyhydroxide with oxygen vacancy defects, which enables selective C-N coupling toward standout electrocatalytic urea synthesis activity. Analysis by operando synchrotron radiation-Fourier transform infrared spectroscopy showcases that *CO2NH2 protonation is the potential-determining step for the overall urea formation process. As such, defect engineering is employed to lower the energy barrier for the protonation of the *CO2NH2 intermediate to accelerate urea synthesis. Consequently, the defect-engineered catalyst delivers a high Faradaic efficiency of 51.0%. In conjunction with an in-depth study on the catalytic mechanism, this design strategy may facilitate the exploration of advanced catalysts for electrochemical urea synthesis and other sustainable applications.

Ni single atoms anchored on N-doped carbon nanosheets as bifunctional electrocatalysts for Urea-assisted rechargeable Zn-air batteries

Abstract: The sluggish kinetics of oxygen electrode reactions is a bottleneck for the development of rechargeable Zn-air batteries (ZABs). Herein, we report a bifunctional electrocatalyst synthesized by anchoring individually dispersed Ni single atoms on N-doped carbon nanosheets (Ni SAs-NC), which exhibits an outstanding overall performance for oxygen reduction reaction (ORR) and urea oxidation reaction (UOR). Based on that, a conceptual urea-assisted rechargeable ZAB by coupling ORR with UOR of a low thermodynamic potential is demonstrated to have significantly decreased charging voltage and high urea elimination rate. The high bifunctional electrocatalytic activities of Ni SAs-NC endow the urea-assisted ZAB with a dramatically increased energy conversion efficiency of 71.8%, which is improved by 17.1% as compares with the conventional ZABs. The successful implementation of Ni SACs based urea-assisted rechargeable ZABs with an improved energy conversion efficiency may prompt ZAB technology towards practical applications.

Strategies for Designing More Efficient Electrocatalysts towards Urea Oxidation Reaction

Abstract: Urea oxidation reaction (UOR) is a pivotal half-reaction for urea-assisted water splitting to produce hydrogen, direct urea fuel cells and electrochemical degradation of urea-containing wastewater. However, the intrinsic sluggish kinetics...

Identifying and tailoring C–N coupling site for efficient urea synthesis over diatomic Fe–Ni catalyst

Abstract: Abstract Electrocatalytic urea synthesis emerged as the promising alternative of Haber–Bosch process and industrial urea synthetic protocol. Here, we report that a diatomic catalyst with bonded Fe–Ni pairs can significantly improve the efficiency of electrochemical urea synthesis. Compared with isolated diatomic and single-atom catalysts, the bonded Fe–Ni pairs act as the efficient sites for coordinated adsorption and activation of multiple reactants, enhancing the crucial C–N coupling thermodynamically and kinetically. The performance for urea synthesis up to an order of magnitude higher than those of single-atom and isolated diatomic electrocatalysts, a high urea yield rate of 20.2 mmol h −1 g −1 with corresponding Faradaic efficiency of 17.8% has been successfully achieved. A total Faradaic efficiency of about 100% for the formation of value-added urea, CO, and NH 3 was realized. This work presents an insight into synergistic catalysis towards sustainable urea synthesis via identifying and tailoring the atomic site configurations.

Self‐Derivation and Surface Reconstruction of Fe‐Doped Ni3S2 Electrode Realizing High‐Efficient and Stable Overall Water and Urea Electrolysis

Abstract: Exploring earth‐abundant, highly effective, and stable electrocatalysts for overall water and urea electrolysis is urgent and essential for developing hydrogen energy technology. Herein, a simple self‐derivation method is used to fabricate a Fe‐doped Ni3S2 electrode. The electrode exhibits an impressive trifunctional catalyst, with low overpotentials of 290, 198, and 254 mV at 100 mA cm−2 for the oxygen evolution reaction (OER), urea oxidation reaction (UOR), and hydrogen evolution reaction (HER). The durability is higher than 3500 h (146 days) at 100 mA cm−2 for the OER without obvious change. In situ Raman spectra reveal the incorporation of Fe inhibited S dissolution and facilitates the catalyst reconstruction. The density functional theory calculations indicate that the doping of Fe optimizes the adsorption of the rate‐determining step and the d‐band center is closer to the Fermi level, which accelerates the OER process. The two‐electrode electrolyzer needs the cell voltages of only 1.76 and 1.57 V to achieve a current density of 100 mA cm−2 and remarkable durability for more than 500 h at 100 and 500 mA cm−2 for overall water and urea splitting. This work holds great promise for industrial water and urea splitting applications.

Self-healable dynamic poly(urea-urethane) gel electrolyte for lithium batteries

Abstract: Hindered urea bonds are introduced as self-healing units in a polymer electrolyte for Li-metal batteries. Differently from standard commercial separators, the poly(urea-urethane) system works for hundreds of cycles after several damage/healing steps.

Identifying and tailoring C–N coupling site for efficient urea synthesis over diatomic Fe–Ni catalyst

Abstract: Abstract Electrocatalytic urea synthesis emerged as the promising alternative of Haber–Bosch process and industrial urea synthetic protocol. Here, we report that a diatomic catalyst with bonded Fe–Ni pairs can significantly improve the efficiency of electrochemical urea synthesis. Compared with isolated diatomic and single-atom catalysts, the bonded Fe–Ni pairs act as the efficient sites for coordinated adsorption and activation of multiple reactants, enhancing the crucial C–N coupling thermodynamically and kinetically. The performance for urea synthesis up to an order of magnitude higher than those of single-atom and isolated diatomic electrocatalysts, a high urea yield rate of 20.2 mmol h −1 g −1 with corresponding Faradaic efficiency of 17.8% has been successfully achieved. A total Faradaic efficiency of about 100% for the formation of value-added urea, CO, and NH 3 was realized. This work presents an insight into synergistic catalysis towards sustainable urea synthesis via identifying and tailoring the atomic site configurations.

Understanding the Site‐Selective Electrocatalytic Co‐Reduction Mechanism for Green Urea Synthesis Using Copper Phthalocyanine Nanotubes

Abstract: Green synthesis of urea under ambient conditions by electrochemical co‐reduction of N2 and CO2 gases using effective electrocatalyst essentially pushes the conventional two steps (N2 + H2 = NH3 and NH3 + CO2 = CO(NH2)2) industrial process at high temperature and high pressure, to the brink. The single step electrochemical green urea synthesis process has hit a roadblock due to the lack of efficient and economically viable electrocatalyst with multiple active sites for dual reduction of N2 and CO2 gas molecules to urea. Herein, copper phthalocyanine nanotubes (CuPc NTs) having multiple active sites (such as metal center, Pyrrolic‐N3, Pyrrolic‐N2, and Pyridinic‐N1) as an efficient electrocatalyst which exhibits urea yield of 143.47 µg h–1 mg–1cat and faradaic efficiency of 12.99% at –0.6 V versus reversible hydrogen electrode by co‐reduction of N2 and CO2 are reported. Theoretical calculation suggests that Pyridinic‐N1 and Cu centers are responsible to form CN bonds for urea by co‐reduction of N2 to NN* and CO2 to *CO, respectively. This study provides the new mechanistic insight about the successful electro‐reduction of dual gases (N2 and CO2) in a single molecule as well as rational design of efficient noble metal‐free electrocatalyst for the synthesis of green urea.

Tuning the Coordination Structure of CuNC Single Atom Catalysts for Simultaneous Electrochemical Reduction of CO2 and NO3– to Urea

Abstract: Closing both the carbon and nitrogen loops is a critical venture to support the establishment of the circular, net‐zero carbon economy. Although single atom catalysts (SACs) have gained interest for the electrochemical reduction reactions of both carbon dioxide (CO2RR) and nitrate (NO3RR), the structure–activity relationship for Cu SAC coordination for these reactions remains unclear and should be explored such that a fundamental understanding is developed. To this end, the role of the Cu coordination structure is investigated in dictating the activity and selectivity for the CO2RR and NO3RR. In agreement with the density functional theory calculations, it is revealed that Cu‐N4 sites exhibit higher intrinsic activity toward the CO2RR, whilst both Cu‐N4 and Cu‐N4−x‐Cx sites are active toward the NO3RR. Leveraging these findings, CO2RR and NO3RR are coupled for the formation of urea on Cu SACs, revealing the importance of *COOH binding as a critical parameter determining the catalytic activity for urea production. To the best of the authors’ knowledge, this is the first report employing SACs for electrochemical urea synthesis from CO2RR and NO3RR, which achieves a Faradaic efficiency of 28% for urea production with a current density of −27 mA cm–2 at −0.9 V versus the reversible hydrogen electrode.

A review of hetero-structured Ni-based active catalysts for urea electrolysis

Abstract: Urea electrooxidation has received considerable attention because of its tremendous practical application in environmental protection and energy regeneration. As an electrochemical reaction, the catalytic performance of urea oxidation is highly...

Nitrogen recycling via gut symbionts increases in ground squirrels over the hibernation season

Abstract: Hibernation is a mammalian strategy that uses metabolic plasticity to reduce energy demands and enable long-term fasting. Fasting mitigates winter food scarcity but eliminates dietary nitrogen, jeopardizing body protein balance. Here, we reveal gut microbiome–mediated urea nitrogen recycling in hibernating thirteen-lined ground squirrels (Ictidomys tridecemlineatus). Ureolytic gut microbes incorporate urea nitrogen into metabolites that are absorbed by the host, with the nitrogen reincorporated into the squirrel’s protein pool. Urea nitrogen recycling is greatest after prolonged fasting in late winter, when urea transporter abundance in gut tissue and urease gene abundance in the microbiome are highest. These results reveal a functional role for the gut microbiome during hibernation and suggest mechanisms by which urea nitrogen recycling may contribute to protein balance in other monogastric animals. Description While they sleep Hibernation has evolved to remove animals from seasonal periods that are especially challenging for survival. Despite this protective feature, hibernation poses its own challenges because of the extensive fasting period. One particularly challenging aspect is the lack of dietary nitrogen, which can lead to protein imbalance. Regan et al. looked at gut microbiome activity in hibernating thirteen-lined ground squirrels and found that symbionts recycled nitrogen from urea into their own metabolites, which were then incorporated by the squirrels, allowing them to maintain protein balance (see the Perspective by Sommer and Bäckhed). These results reveal the importance of the gut microbiome to hibernation and suggest that gut microbes could play such a role in other species. —SNV Gut microbiome–mediated urea nitrogen recycling helps ground squirrels survive prolonged fasting during hibernation.

Host-Guest Molecular Interaction Promoted Urea Electrosynthesis over Precisely Designed Conductive Metal-Organic Frameworks

Abstract: Highly selective electrocatalytic activation of N2 and CO2 to synthesis value-added urea via C-N coupling reaction is a top challenge reaction that is largely retarded by poor chemisorption and coupling...

Identification and manipulation of dynamic active site deficiency-induced competing reactions in electrocatalytic oxidation processes

Abstract: A detrimental competition between the urea oxidation reaction (UOR) and oxygen evolution reaction is identified. Strategies are proposed to alleviate such competition and boost the performance of the UOR and other organic compound oxidation reactions.

Oxide-Derived Core-Shell Cu@Zn Nanowires for Urea Electrosynthesis from Carbon Dioxide and Nitrate in Water.

Abstract: Urea electrosynthesis provides an intriguing strategy to improve upon the conventional urea manufacturing technique, which is associated with high energy requirements and environmental pollution. However, the electrochemical coupling of NO3- and CO2 in H2O to prepare urea under ambient conditions is still a major challenge. Herein, self-supported core-shell Cu@Zn nanowires are constructed through an electroreduction method and exhibit superior performance toward urea electrosynthesis via CO2 and NO3- contaminants as feedstocks. Both 1H NMR spectra and liquid chromatography identify urea production. The optimized urea yield rate and Faradaic efficiency over Cu@Zn can reach 7.29 μmol cm-2 h-1 and 9.28% at -1.02 V vs RHE, respectively. The reaction pathway is revealed based on the intermediates detected through in situ attenuated total reflection Fourier transform infrared spectroscopy and online differential electrochemical mass spectrometry. The combined results of theoretical calculations and experiments prove that the electron transfer from the Zn shell to the Cu core can not only facilitate the formation of *CO and *NH2 intermediates but also promote the coupling of these intermediates to form C-N bonds, leading to a high faradaic efficiency and yield of the urea product.

Defect engineering technique for the fabrication of LaCoO3 perovskite catalyst via urea treatment for total oxidation of propane

Abstract: The low defect content and poor oxygen mobility of perovskite catalysts limit its application in VOC elimination. Herein, we report a strategy involving defect engineering route following an easy urea treatment method to enhance the propane oxidation performance of perovskite catalysts. The constructed LaCoO3-D43 exhibits superior catalytic activity (T90 = 309.3 °C), the T90 value is 150 °C lower than that of LaCoO3, and excellent thermal stability against CO2 and H2O. Experimental results revealed that the urea pyrolysis resulted in the generation of La and O defects and rich surface-active Co species in high-valence states, increasing the utilization of Co active sites. DFT calculations show that the exposed Co surface is conducive to the adsorption and dissociation of oxygen and propane. This work provides a defect engineering strategy to effectively activate perovskite catalysts performance, and can be generalized for the fabrication of other types of perovskite catalysts.

Enzyme-Photocatalyst Tandem Microrobot Powered by Urea for Escherichia coli Biofilm Eradication.

Abstract: Urinary-based infections affect millions of people worldwide. Such bacterial infections are mainly caused by Escherichia coli (E. coli) biofilm formation in the bladder and/or urinary catheters. Herein, the authors present a hybrid enzyme/photocatalytic microrobot, based on urease-immobilized TiO2 /CdS nanotube bundles, that can swim in urea as a biocompatible fuel and respond to visible light. Upon illumination for 2 h, these microrobots are able to remove almost 90% of bacterial biofilm, due to the generation of reactive radicals, while bare TiO2 /CdS photocatalysts (non-motile) or urease-coated microrobots in the dark do not show any toxic effect. These results indicate a synergistic effect between the self-propulsion provided by the enzyme and the photocatalytic activity induced under light stimuli. This work provides a photo-biocatalytic approach for the design of efficient light-driven microrobots with promising applications in microbiology and biomedicine.

Carbon nanotubes with fluorine-rich surface as metal-free electrocatalyst for effective synthesis of urea from nitrate and CO2

Abstract: In this work, carbon nanotubes with fluorine-rich surface are firstly developed as advanced metal-free catalysts for the electrocatalytic synthesis of urea via co-activation of CO 2 and NO 3 - under ambient conditions. A high yield rate of 6.36 mmol h −1 g cat. −1 with a corresponding Faradaic efficiency of 18.0% was achieved for the urea formation at − 0.65 V vs . reversible hydrogen electrode. Density functional theory calculations indicate the formation of *CO and *NH 2 intermediates is favorable on F-doped C active sites (“C-F 2 ” moieties), facilitating the C-N coupling reaction to form urea. F doped CNTs as the first C-MFEC for electrocatalytic urea synthesis by co-activation of CO 2 and NO 3 - under ambient conditions, which shows the possibilities for coupling reactions even beyond the urea synthesis. • Carbon nanotubes with fluorine-rich surface are firstly developed as advanced metal-free electrocatalysts for urea synthesis. • A urea yield rate up to 6.36 mmol h −1 g cat. −1 was achieved for F -rich CNTs catalyzed urea synthesis from NO 3 - with CO 2 . • “C-F 2 moieties” on F-rich CNTs promote the formation of *CO and *NH 2 intermediates for C-N coupling for urea generation.

Enhanced electrocatalytic activity of a layered triple hydroxide (LTH) by modulating the electronic structure and active sites for efficient and stable urea electrolysis

Abstract: NiCoFe-LTH nanosheet arrays on a nickel foam substrate act as an efficient and stable electrocatalyst for urea electrolysis, which needs only 1.49 V for 10 mA cm−2.