Urea Electro-oxidation Reaction Research Articles

Metallic nonstoichiometric WO3–x-decorated NiFe-layered double hydroxide for boosted urea electro-oxidation reaction: the facilitated dynamics and increasing active sites

Metallic nonstoichiometric WO3–x-decorated NiFe-layered double hydroxide for boosted urea electro-oxidation reaction: the facilitated dynamics and increasing active sites

In Situ Assembly of a Superaerophobic CoMn/CuNiP Heterostructure as a Trifunctional Electrocatalyst for Ampere-Level Current Density Urea-Assisted Hydrogen Production.

Urea electrolysis is a promising energy-efficient hydrogen production process with environmental benefits, but the lack of efficient and sustainable ampere-level current density electrocatalysts fabricated through simple methods is a major challenge for commercialization. Herein, we present an efficient and stable heterostructure electrocatalyst for full urea and water electrolysis in a convenient and time-efficient preparation manner. Overall, superhydrophilic/superaerophobic CoMn/CuNiP/NF exhibits exceptional performance for the hydrogen evolution reaction (HER) (-33.8, -184.4, and -234.8 mV at -10, -500, and -1000 mA cm-2, respectively), urea electro-oxidation reaction (UOR) [1.28, 1.43, and 1.51 V (vs RHE) at 10, 500, and 1000 mA cm-2, respectively], and oxygen evolution reaction (OER) [1.45, 1.67, and 1.74 V (vs RHE) at 10, 500, and 1000 mA cm-2, respectively]. Moreover, the superaerophobic CoMn/CuNiP/NF demonstrates promising potential in full urea (1.33, 1.57, and 1.60 V at 10, 500, and 1000 mA cm-2, respectively) and water (1.46 V, 1.78, and 1.86 at 10, 500, and 1000 mA cm-2, respectively) electrolysis. Based on X-ray photoelectron spectroscopy results, it was determined that the surface of the CoMn/CuNiP electrode was rich in redox pairs such as Ni2+/Ni3+, Cu+/Cu2+, Co2+/Co3+, and Mn2+/Mn3+, which are crucial for the formation of active sites for the OER and UOR, such as NiOOH, MnOOH, and CoOOH, thereby enhancing the catalytic activity. Besides, the in situ assembled CoMn/CuNiP/NF displayed highly stable performance for HER, OER, and UOR with high Faradaic efficiency for over 500 h. This research offers a simple and efficient method for manufacturing a high-efficiency and stable trifunctional electrocatalyst capable of delivering ampere-level current density in urea-assisted hydrogen production. Our density functional theory calculations reveal the potential of CoMn/CuNiP as an effective catalyst, enhancing the electronic properties and catalytic performance. The near-zero Gibbs free-energy change for HER underscores its promise, while reduced CO2 desorption energies and charge redistribution support efficient UOR. These findings signify CoMn/CuNiP's potential for electrochemical applications.

Self-supported Pt nanoparticles-NiFeP nanosheets arrays nanohybrid with hydrophilic surface towards urea electrolysis

Urea-assisted water electrolysis is a clean, sustainable, and energy-saving method towards hydrogen production. However, the development of earth-abundant, stable, and highly active bifunctional catalysts towards urea electrolysis is still a significant technical challenge. Herein, the highly dispersed Pt nanoparticles decorated NiFeP nanosheets arrays on nickel foam (Pt-NiFeP/NF) electrode is rationally designed, which combines the advantages of superhydrophilic interface, ultrathin nanostructure and open three-dimensional (3D) architecture. Consequently, Pt-NiFeP/NF displays a remarkable electroactivity towards both hydrogen evolution reaction (HER) and urea electrooxidation reaction (UEOR), which only needs the overpotential of 32 mV to achieve the current density of 10 mA cm−2 towards HER, and drives a current density of 50 mA cm−2 at 1.38 V towards UEOR. More importantly, the urea electrolysis system assembled with Pt-NiFeP/NF only requires a cell voltage of 1.41 V to achieve a current density of 100 mA cm−2, much lower than the traditional water electrolysis (1.94 V). This work promotes the application of Pt nanoparticles decorated bimetallic phosphides as a bifunctional catalyst towards urea-rich wastewater treatment and green electrochemical hydrogen production.

Ni-based metal-organic framework sensor material for urea detection: Mechanistic insights and performance

A mechanistic study of the metal-organic framework nickel-hexahydroxytriphenylene [Ni3(HHTP)2]n as an active catalyst material for electrochemical urea sensing is reported, together with the evaluation of its performance. Urea sensing is a crucial technology for the life quality of people facing kidney disease. Through the quantification of urea in saliva, the monitoring of the progress of kidney disease could be enabled. [Ni3(HHTP)2]n can detect urea via urea electro-oxidation reaction. The urea electro-oxidation on [Ni3(HHTP)2]n follows an EC’ mechanism. [Ni3(HHTP)2]n is electrochemically transformed into Ni(OH)2, the catalytic intermediate of Ni in alkaline electrolyte, and the reduction step of Ni3+ to Ni2+ limited by the urea electro-oxidation reaction. The transformation leads to a disintegration of the metal-organic framework due to oxygen evolution. As urea inhibits oxygen evolution, the degradation is also inhibited. Our results demonstrated a competitive sensor when compared to the benchmarking, with a sensitivity of 1.797 mA/cm2∙mM Urea, the limit of detection of 3.5 µM, linear range between 0.01 mM and 1 mM with a correlation coefficient of 0.991 and selectivity towards Na+, K+, Cl−, creatinine, uric acid, and low concentrations of glucose.

Water splitting by CoFeLDH@NiFeS nanoelectrocatalyst assisted urea electrooxidation reaction

In this paper, NiFeS@CoFeLDH nanostructure was synthesized for the first time by electrochemical method in two steps. In the first stage, the first layer of NiFeS was deposited on the nickel foam (NF) substrate, and in the second stage, the second layer of cobalt-iron layered double hydroxide (CoFeLDH)by controlling the electrodeposition condition was deposited on the first. The deposition time and potential were optimized. The optimized NiFeS@CoFeLDH coating on NF has promising hydrogen evolution reaction (HER) activity, which exhibits small overpotentials of − 191.5, and − 304.0, at the current densities of − 10, and − 100 mA. cm−2, respectively. Furthermore, the synthesized NiFeS@CoFeLDH electrocatalyst only needs 358 mV overpotentials to operate at a current density of 10 mA. cm−2 indicating its great performance for the urea oxidation reaction (UOR). The electrode stability was examined at an industrial scale current density of − 100 and 10 mA. cm−2 for HER and UOR respectively, which showed a very stable response for at least 10 h. The results showed that the simultaneous application of NiFeS and CoFeLDH electrocatalysts has a synergistic effect that increases the surface-to-volume ratio and improves the active sites. According to high performance for HER and UOR and also simple, fast, and binder-free synthesis without using expensive materials for preparing the electrocatalyst layer, the proposed electrode can be used as a good candidate for water splitting in the presence of urea.

Enhanced hydrogen production via urea electrolysis over Ni-NiO electrodeposited on Ti mesh

The sluggish kinetics of anodic oxygen evolution reaction (OER) is regarded as the main bottleneck for ineffective hydrogen production efficiency, limiting the industrial application of electrochemical water splitting. Substituting the OER by urea electrooxidation reaction (UOR) and simultaneously developing highly active and economical bifunctional electrocatalyst for UOR and hydrogen evolution reaction (HER) is a promising method to realize energy-saving hydrogen production and urea-rich wastewater abatement. Herein, self-supporting Ni-NiO film grown on Ti mesh (Ni-NiO/TM) was successfully prepared by a facile cathodic electrodeposition method with using nickel acetate as the only raw material. Electrodeposition process was optimized by modulating the electrodeposition time and potential. x-ray diffraction, scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy and Raman characterization revealed the optimized Ni-NiO/TM was comprised of crystalline Ni and amorphous NiO and its morphology exhibited nanosphere structure, assembled by nanosheets. Ni-NiO/TM sample prepared under the potential of −1.5 V and deposition time of 10 min illustrated the lowest UOR potential of 1.34 V at 50 mA cm−2 and robust stability, superior to the recently reported literatures. Furthermore, the HER potential was only −0.235 V to drive the current density of 50 mA cm−2. The cell voltage of urea-assisted electrolysis for hydrogen production in Ni-NiO/TM||Ni-NiO/TM two-electrode system only required 1.56 V to deliver 50 mA cm−2, obviously lower than that (>1.72 V) for overall water splitting. This work demonstrated the potential of Ni-based material as bifunctional electrocatalyst for energy-saving H2 production by urea-rich wastewater electrolysis.

FeNi supported on carbon sponge for efficient urea oxidation in direct urea fuel cell

The direct urea fuel cell (DUFC) is a power generation equipment with urea-rich wastewater or urine as fuel source. It has the unique ability to purify sewage while simultaneously generating electricity, making it a highly efficient and environmentally friendly option. In this paper, pomegranate seed-like Ni nano-blocks and Fe nanosheets were synthesized by electrodeposition and chemical reduction and attached to the carbonized melamine sponge matrix. The N-doped carbon sponge (NCS) provided a large number of polyhedral holes, which allowed for efficient gas escape through channels. The combination of Fe reduces the initial urea oxidation potential, reaction activation energy and reaction resistance. The synthesized FeNi supported on N-doped carbon sponge composite (FeNi@NCS) has a catalytic current density of 625 mA cm−2 and a Tafel slope of 42.51 mV dec−1 for urea electrooxidation reaction (UOR). Assembling the direct urine-hydrogen peroxide fuel cell (DUrHPFC) resulted in the highest performance output. The open circuit voltage (OCV) was 0.98 V, and the peak power density reached 9.61 mW cm−2. The results show that the prepared catalyst provides an opportunity to solve the problems that hinder the development of urea green cycle at present.

Boosting urea electrooxidation on oxyanion-engineered nickel sites via inhibited water oxidation

Renewable energy-based electrocatalytic oxidation of organic nucleophiles (e.g.methanol, urea, and amine) are more thermodynamically favourable and, economically attractive to replace conventional pure water electrooxidation in electrolyser to produce hydrogen. However, it is challenging due to the competitive oxygen evolution reaction under a high current density (e.g., >300 mA cm−2), which reduces the anode electrocatalyst’s activity and stability. Herein, taking lower energy cost urea electrooxidation reaction as the model reaction, we developed oxyanion-engineered Nickel catalysts to inhibit competing oxygen evolution reaction during urea oxidation reaction, achieving an ultrahigh 323.4 mA cm−2 current density at 1.65 V with 99.3 ± 0.4% selectivity of N-products. In situ spectra studies reveal that such in situ generated oxyanions not only inhibit OH− adsorption and guarantee high coverage of urea reactant on active sites to avoid oxygen evolution reaction, but also accelerate urea’s C − N bond cleavage to form CNO − intermediates for facilitating urea oxidation reaction. Accordingly, a comprehensive mechanism for competitive adsorption behaviour between OH− and urea to boost urea electrooxidation and dynamic change of Ni active sites during urea oxidation reaction was proposed. This work presents a feasible route for high-efficiency urea electrooxidation reaction and even various electrooxidation reactions in practical applications.

MagnetoElectroCatalysis: A new approach for urea electro-oxidation reaction on nickel-iron oxide catalyst

The present work investigates the effect of external alternating magnetic field (AMF) on the electrocatalytic activity of nickel (Ni), iron oxide magnetic nanoparticles (MNP), and Ni-MNP nanoparticles in the urea electro-oxidation reaction (UER) through chronoamperometry (CA) with amplitudes of AMF between 14.9 and 88.9 mT and a frequency of 224 kHz. Results indicate that the AMF between 29.8 and 88.9 mT had a significant impact on the efficiency of UER, increasing the current obtained from Ni-MNP nanoparticles supported on carbon cloth (Ni-MNP/CC) by up to 52.5%. Moreover, a linear relationship between the UER current and AMF amplitude was observed. The significant enhancement of the current in the UER process with Ni-MNP/CC as catalyst under the AMF is attributed to the local heat generated by MNP nanoparticles, boosting the UER process on nickel nanoparticles. This work represents the first investigation of AMF on the UER process.

Facile synthesis of NiCo2S4@Ni3Se2 nanocomposites for supercapacitor and electrocatalytic H2 production

In this work, NiCo2S4@Ni3Se2 nanocomposites were fabricated with facile hydrothermal + electrodeposition method on Ni foam and the performances of energy storage and hydrogen evolution reaction were systematically investigated. As the electrode material for supercapacitor, NiCo2S4@Ni3Se2 demonstrated a specific capacitance of 9.82F cm−2 at 3 mA cm−2. The corresponding asymmetric supercapacitor exhibited the specific capacitance of 5.18F cm−2 at 3 mA cm−2 and retained 66.6% with current density increasing to 20 mA cm−2. Moreover, NiCo2S4@Ni3Se2-1.0–5 exhibited an outstanding electrocatalytic activation with low potential of 1.396 V for urea electrooxidation reaction (UOR) and 1.415 V for ethanol oxidation reaction (EOR) at current density of 10 mA cm−2 and the corresponding two-electrode overall water splitting potential reached at 1.566 V in 1 M KOH + 0.1 M urea. Thus, this study demonstrates the promising practical applications of NiCo2S4@Ni3Se2 nanocomposites for energy storage and hydrogen evolution reaction.

Nickel Nanoparticles Supported on Carbon Cloth via Pulsed Laser Deposition as an Effective Catalyst for Urea Electro-oxidation Reaction

Nickel Nanoparticles Supported on Carbon Cloth via Pulsed Laser Deposition as an Effective Catalyst for Urea Electro-oxidation Reaction

Highly Selective Electrooxidation of Urea to Nitrogen on Copper/Nickel Boride Interface under Alkaline Condition

Urea electrooxidation reaction (UOR) plays an important role in environmental protection and energy regeneration. The extensively studied nickel-based catalysts exhibit good activity for UOR, but urea is more prone to be overelectrooxidized to another pollutant NOx– (x = 2, 3). Herein, the Cu/Ni-B interface catalyst is presented. The introduction of Cu significantly enhances the Faradaic efficiency of N2 (nearly 70% at 1.70 V versus RHE). Electrochemical tests and in situ Raman spectroscopy results show that the introduction of Cu significantly affects the density of OH* species on the catalyst in the UOR process. It is proposed that with a moderate decrease in OH* density, the catalyst can provide enough sites for urea molecules to allow simultaneous adsorption of the two N atoms, facilitating the process of N-N coupling to form N2. This work is also instructive for the design of electrocatalysts for other nucleophile electrooxidation reactions.

Synthesis of FeCo2O4@Co3O4 nanocomposites and their electrochemical catalytical performaces for energy-saving H2 prodcution

In this study, FeCo2O4@Co3O4 bifunctional catalysts with a unique structure combining nanosheets and nanowires were prepared on nickel foam by a simple hydrothermal + annealing method. The catalysts exhibited excellent catalytic activity for hydrogen production during urea electrooxidation reaction (UOR) and ethanol oxidation reaction (EOR). For UOR, the potential at 10 mA/cm2 current density is 1.387 V and the tafel slope is 67 mV/dec. In the configured two-electrode electrolytic cell, the FeCo2O4@Co3O4 catalysts in the UOR and EOR processes required only 1.425 and 1.471 V, respectively, to produce a current density of 10 mA/cm2, which is much less than that of the (oxygen evolution reaction) OER (1.640 V). In addition, the current density remained stable at a fixed potential during a long time (20 h) i-t test in the urea solution.

Accelerating charge transfer for Ni(OH)2 through chlorine-anion decoration in the urea electrooxidation reaction

Chlorine-anion-modified Ni(OH)2 (Cl32–Ni(OH)2) has low crystallinity, a large specific surface area and more oxygen defects, resulting in enhanced charge transfer, ultimately facilitating the urea oxidation reaction.

Building dual-phased Ni2P–Ni2P4O12electrocatalysts for efficient urea oxidation reaction

Ni2P–Ni2P4O12structure with abundant mesopores demonstrates excellent catalytic activity toward alkaline urea electro-oxidation reaction.

Molybdenum carbide/Ni nanoparticles-incorporated carbon nanofibers as effective non-precious catalyst for urea electrooxidation reaction

In this study, molybdenum carbide and carbon were investigated as co-catalysts to enhance the nickel electro-activity toward urea oxidation. The proposed electrocatalyst has been formulated in the form of nanofibrous morphology to exploit the advantage of the large axial ratio. Typically, calcination of electropsun polymeric nanofibers composed of poly(vinyl alcohol), molybdenum chloride and nickel acetate under vacuum resulted in producing good morphology molybdenum carbide/Ni NPs-incorporated carbon nanofibers. Investigation on the composition and morphology of the proposed catalyst was achieved by XRD, SEM, XPS, elemental mapping and TEM analyses which concluded formation of molybdenum carbide and nickel nanoparticles embedded in a carbon nanofiber matrix. As an electrocatalyst for urea oxidation, the electrochemical measurements indicated that the proposed composite has a distinct activity when the molybdenum content is optimized. Typically, the nanofibers prepared from electrospun nanofibers containing 25 wt% molybdenum precursor with respect to nickel acetate revealed the best performance. Numerically, using 0.33 M urea in 1.0 M KOH, the obtained current densities were 15.5, 44.9, 52.6, 30.6, 87.9 and 17.6 mA/cm2 for nanofibers prepared at 850 °C from electropsun mats containing 0, 5, 10, 15, 25 and 35 molybdenum chloride, respectively. Study the synthesis temperature of the proposed composite indicated that 1000 °C is the optimum calcination temperature. Kinetic studies indicated that electrooxidation reaction of urea does not follow Arrhenius’s law.

Rational design of double perovskite La2Ni0.5Co0.5MnO6 decorated polyaniline array on MoO3 nanobelts with strong heterointerface boosting oxygen evolution reaction and urea oxidation

The design and implementation of affordable high-performance electrocatalysts for the oxygen evolution reaction (OER) and urea electrooxidation reaction (UOR) are critical for clean and environmentally friendly energy conversion. Herein, we constructed a novel heterostructure interface engineering of double perovskite La2Ni0.5Co0.5MnO6 (LNCM) nanoparticles and MoO3 nanobelt array-supported amorphous polyaniline (PANI; MoO3/P) for high-performance OER and UOR. Structural and morphological analyses confirmed the formation of a heterostructure interface. The optimized La2Ni0.5Co0.5MnO6@MoO3/P (LMP-30) demonstrated electrocatalytic performance with low overpotentials of 300 mV at 10 mA cm−2 (vs RHE) for OER and 0.48 V at 50 mA cm−2 (vs Hg/HgO) for UOR, as well as better stability after testing for 12 h. The improved electrocatalytic performance was attributed to its distinctive hierarchical nanostructure, which had a synergistic effect on modulating the electrical characteristics and an electrochemically active surface area. More importantly, the LNCM nanoparticles on the surface of MoO3/P nanobelts can potentially provide more electrocatalytic active sites, excellent charge transport capacity, enhanced electrical properties, and strong electronic contacts between MoO3/P and LNCM.

High-Valent Ni Species Induced by Inactive MoO2 for Efficient Urea Oxidation Reaction.

The microenvironment tuning of Ni species, a promising non-precious catalyst, is significant in the energy and environmentally relevant urea electro-oxidation reaction (UOR). Herein, we found that the high-valent Ni species induced by the inactive MoO2 in mixed nanocrystals of NiO/MoO2 were effective for urea oxidation. The redox interaction of MoO2 and NiO revealed by the spectroscopic analysis well supported the formation of high-valent Ni species and the changes in the surface chemical state. High catalytic activity and stability for urea oxidation were observed by a series of electrochemical measures compared to the counterpart catalysts of MoO2 and NiO. The optimal NiO/MoO2 hybrid catalyst showed a UOR activity of 73.1 mA cm-2 at 1.50 V, which was about 12-fold that of the NiO catalyst. In addition, largely improved catalytic kinetics and catalytic stability for UOR were also demonstrated. Because of the inactive activity of MoO2 and the low performance of NiO, the largely improved preference can be affirmatively attributed to the efficient catalytic synergism of NiO/MoO2 in the mixed nanocrystals. The current finding clarifies the catalytic promotion effect of the inactive Mo species on Ni-based catalysts for urea oxidation, which would be instructive for Ni/Mo-relevant catalyst development.

Urea electrooxidation-boosted hydrogen production on nitrogen-doped porous carbon nanorod-supported nickel phosphide nanoparticles

Urea electro-oxidation reaction (UEOR)-boosted water electrolysis can supplant the kinetics-restricted oxygen evolution reaction (OER) and provide an energy-saving method of hydrogen generation. However, low UEOR activity and the poisoning issue of the catalyst limit its practical application. Herein, a simple coordination reaction is used to synthesize the dimethylglyoxime-NiⅡ complex (DMG-NiⅡ), which efficiently serves as the initial precursor to synthesize nitrogen-doped carbon nanorod-supported nickel phosphide nanoparticle (Ni2P/N-Cnanorods) nanocomposites. The density functional theory calculations and electrochemical results reveal that nitrogen doping can weaken the adsorption of hydrogen and the generated CO2, resulting in an enhancement of hydrogen evolution reaction (HER) and UEOR activity. In addition, N-doping can also promote the generation of Ni3+, which can further promote the UEOR and HER performance. Concretely, the overpotential for the HER on Ni2P/N-Cnanorods-2h nanocomposites is only 201 mV at 10 mA cm−2, and the onset potential of the UEOR on Ni2P/N-Cnanorods-2h nanocomposites is only 1.34 V. Additionally, the Ni2P/N-Cnanorods nanocomposites also show excellent long-term stability due to the introduction of nitrogen-doped carbon material. Consequently, the symmetric Ni2P/N-Cnanorods-2h||Ni2P/N-Cnanorods-2h urea electrolyzer requires 1.41 V of electrolysis voltage for urea electrolysis, which can be applied in energy-saving H2 production and environment purification.

Tuning interface density and electronic structure of NiS/Ni3S4 by Mo, Co co-doping for efficient urea electrooxidation reaction

Mo, Co co-doped NiS/Ni 3 S 4 with high activity, low onset potential, fast kinetics, more active sites, excellent intrinsic catalytic activity and stability demonstrates excellent catalytic activity toward alkaline urea electrolysis. • Mo, Co co-doped NiS/Ni 3 S 4 heterojunction with 3D flower-like shape assembled by 2D ultrathin nanosheets are successfully prepared. • The amount of heterointerfaces and the electronic interaction are simultaneously modified by adjusting experimental parameters. • Mo, Co co-doped NiS/Ni 3 S 4 catalysts exhibit rich exposed active sites and facilitated electron transportation. • The assembled direct urea hydrogen peroxide fuel cell (DUHPFC) employing Mo 0.05 ,Co-NSH has an open-circle voltage (OCV) of 0.86 V and a maximum power density ( P max ) of 5.96 mW cm −2 . Electrocatalysts exhibiting impressive catalytic capability and strong stability for urea oxidation reaction (UOR) are highly desired for direct urea fuel cells (DUFCs). Herein, a series of flower-like Mo, Co co-doped NiS/Ni 3 S 4 heterostructure (Mo, Co-NSH) are controllable synthesized by a one-step hydrothermal method and utilized as catalysts for UOR. Taking advantages of massive heterojunctions, tunable electronic configuration and hierarchical flower-like topological structure together, the optimized component demonstrates advanced UOR performance compared to pure NiS/Ni 3 S 4 and mono Co/Mo element doped NiS/Ni 3 S 4 , it delivers 147.1 mA cm −2 at 1.6 V vs. RHE and works for more than 18 h without decay. The assembly direct urea hydrogen peroxide fuel cell (DUHPFC) with Mo 0.05 , Co-NSH catalyst has an open-circuit voltage of 0.86 V and a maximum power density of 5.96 mW cm −2 at 27 °C. The work provides a promising avenue for exploiting efficient electrocatalysts on both multi-metal doping and heterojunction engineering for electrochemical energy conversion and sewage treatment applications.