Nickel diselenide nanoflakes give superior urea electrocatalytic conversion

P-NiFe2O4/N-Doped Carbon Nanotubes/NiFe Multi-Phase Heterojunctions for Overall Water Splitting and Urea Electrolysis

The design and construction of highly efficient electrocatalysts for overall water splitting and urea electrolysis are significantly important for promoting energy conversion and realizing green hydrogen production. In this work, we constructed a multi-phase heterojunction through a simple hydrothermal and phosphorization process. The P-doped NiFe2O4 (P-NiFe2O4) nanoparticles were uniformly anchored on the bamboo-like N-doped carbon nanotubes (NCNTs) grown via a NiFe-alloy autocatalysis. The electronic structure and coordination environment of active species were optimized by the synergistic action of P doping, well-dispersed ultrafine NiFe2O4, and NCNTs matrix with good conductivity, enhancing their quantity and activity for electrocatalysis. Consequently, the P-NiFe2O4/NCNTs/NiFe exhibits excellent HER and OER activities with an overpotential of 111 and 266 mV at 10 mA cm-2 in 1 M KOH, respectively. The symmetrical overall water-splitting cell using P-NiFe2O4/NCNTs/NiFe as both anode and cathode delivers 10 mA cm-2 at a voltage of 1.604 V in 1 M KOH. Notably, the two-electrode cell requires a low voltage of 1.467 V to achieve a current density of 10 mA cm-2 in 1 M KOH solution with 0.6 M urea. This designed catalysts display outstanding reaction kinetics and catalytic stability. This work provides useful guidance for applying transition metal-based catalysts for hydrogen production.

Engineering Amorphous/Crystalline Ru(OH)3/CoFe-Layered Double Hydroxide for Hydrogen Evolution at 1000 mA cm-2

For large-scale industrial applications, it is highly desirable to create effective, economical electrocatalysts with long-term stability for the hydrogen evolution reaction (HER) at a large current density. Herein, we report a unique motif with crystalline CoFe-layered hydroxide (CoFe-LDH) nanosheets enclosed by amorphous ruthenium hydroxide (a-Ru(OH)₃/CoFe-LDH) to realize the efficient hydrogen production at 1000 mA cm^-2, with a low overpotential of 178 mV in alkaline media. During the continuous HER process for 40 h at such a large current density, the potential remains almost constant with only slight fluctuations, indicating good long-term stability. The remarkable HER performance can be attributed to the charge redistribution caused by abundant oxygen vacancies in a-Ru(OH)₃/CoFe-LDH. The increased electron density of states lowers the charge-transfer resistance and promotes the formation and release of H₂ molecules. The water-splitting electrolyzer with a-Ru(OH)₃/CoFe-LDH as both an anode and a cathode in 1.0 M KOH demonstrates stable hydrogen production and a 100% faradic efficiency. The design strategy of interface engineering in this work will inspire the design of practical electrocatalysts for water splitting on an industrial scale.

Construction of Nitrogen-Doped Biphasic Transition-Metal Sulfide Nanosheet Electrode for Energy-Efficient Hydrogen Production via Urea Electrolysis

Urea-assisted hybrid water splitting is a promising technology for hydrogen (H₂ ) production, but the lack of cost-effective electrocatalysts hinders its extensive application. Herein, it is reported that Nitrogen-doped Co₉ S₈ /Ni₃ S₂ hybrid nanosheet arrays on nickel foam (N-Co₉ S₈ /Ni₃ S₂ /NF) can act as an active and robust bifunctional catalyst for both urea oxidation reaction (UOR) and hydrogen evolution reaction (HER), which could drive an ultrahigh current density of 400 mA cm^-2 at a low working potential of 1.47 V versus RHE for UOR, and gives a low overpotential of 111 mV to reach 10 mA cm^-2 toward HER. Further, a hybrid water electrolysis cell utilizing the synthesized N-Co₉ S₈ /Ni₃ S₂ /NF electrode as both the cathode and anode displays a low cell voltage of 1.40 V to reach 10 mA cm^-2 , which can be powered by an AA battery with a nominal voltage of 1.5 V. The density functional theory (DFT) calculations decipher that N-doped heterointerfaces can synergistically optimize Gibbs free energy of hydrogen and urea, thus accelerating the catalytic kinetics of HER and UOR. This work significantly advances the development of the promising cobalt-nickel-based sulfide as a bifunctional electrocatalyst for energy-saving electrolytic H₂ production and urea-rich innocent wastewater treatment.

Highly efficient overall urea electrolysis via single-atomically active centers on layered double hydroxide

Anodic urea oxidation reaction (UOR) is an intriguing half reaction that can replace oxygen evolution reaction (OER) and work together with hydrogen evolution reaction (HER) toward simultaneous hydrogen fuel generation and urea-rich wastewater purification; however, it remains a challenge to achieve overall urea electrolysis with high efficiency. Herein, we report a multifunctional electrocatalyst termed as Rh/NiV-LDH, through integration of nickel-vanadium layered double hydroxide (LDH) with rhodium single-atom catalyst (SAC), to achieve this goal. The electrocatalyst delivers high HER mass activity of 0.262 A mg^-1 and exceptionally high turnover frequency (TOF) of 2.125 s^-1 at an overpotential of 100 mV. Moreover, exceptional activity toward urea oxidation is addressed, which requires a potential of 1.33 V to yield 10 mA cm^-2, endorsing the potential to surmount the sluggish OER. The splendid catalytic activity is enabled by the synergy of the NiV-LDH support and the atomically dispersed Rh sites (located on the Ni-V hollow sites) as evidenced both experimentally and theoretically. The self-supported Rh/NiV-LDH catalyst serving as the anode and cathode for overall urea electrolysis (1 mol L^-1 KOH with 0.33 mol L^-1 urea as electrolyte) only requires a small voltage of 1.47 V to deliver 100 mA cm^-2 with excellent stability. This work provides important insights into multifunctional SAC design from the perspective of support sites toward overall electrolysis applications.

Recent Development of Nickel-Based Electrocatalysts for Urea Electrolysis in Alkaline Solution

Recently, urea electrolysis has been regarded as an up-and-coming pathway for the sustainability of hydrogen fuel production according to its far lower theoretical and thermodynamic electrolytic cell potential (0.37 V) compared to water electrolysis (1.23 V) and rectification of urea-rich wastewater pollution. The new era of the "hydrogen energy economy" involving urea electrolysis can efficiently promote the development of a low-carbon future. In recent decades, numerous inexpensive and fruitful nickel-based materials (metallic Ni, Ni-alloys, oxides/hydroxides, chalcogenides, nitrides and phosphides) have been explored as potential energy saving monofunctional and bifunctional electrocatalysts for urea electrolysis in alkaline solution. In this review, we start with a discussion about the basics and fundamentals of urea electrolysis, including the urea oxidation reaction (UOR) and the hydrogen evolution reaction (HER), and then discuss the strategies for designing electrocatalysts for the UOR, HER and both reactions (bifunctional). Next, the catalytic performance, mechanisms and factors including morphology, composition and electrode/electrolyte kinetics for the ameliorated and diminished activity of the various aforementioned nickel-based electrocatalysts for urea electrolysis, including monofunctional (UOR or HER) and bifunctional (UOR and HER) types, are summarized. Lastly, the features of persisting challenges, future prospects and expectations of unravelling the bifunctional electrocatalysts for urea-based energy conversion technologies, including urea electrolysis, urea fuel cells and photoelectrochemical urea splitting, are illuminated.

Recent Advancements in Chalcogenides for Electrochemical Energy Storage Applications

Energy storage has become increasingly important as a study area in recent decades. A growing number of academics are focusing their attention on developing and researching innovative materials for use in energy storage systems to promote sustainable development goals. This is due to the finite supply of traditional energy sources, such as oil, coal, and natural gas, and escalating regional tensions. Because of these issues, sustainable renewable energy sources have been touted as an alternative to nonrenewable fuels. Deployment of renewable energy sources requires efficient and reliable energy storage devices due to their intermittent nature. High-performance electrochemical energy storage technologies with high power and energy densities are heralded to be the next-generation storage devices. Transition metal chalcogenides (TMCs) have sparked interest among electrode materials because of their intriguing electrochemical properties. Researchers have revealed a variety of modifications to improve their electrochemical performance in energy storage. However, a stronger link between the type of change and the resulting electrochemical performance is still desired. This review examines the synthesis of chalcogenides for electrochemical energy storage devices, their limitations, and the importance of the modification method, followed by a detailed discussion of several modification procedures and how they have helped to improve their electrochemical performance. We also discussed chalcogenides and their composites in batteries and supercapacitors applications. Furthermore, this review discusses the subject’s current challenges as well as potential future opportunities.

Facile Fabrication of a Foamed Ag3CuS2 Film as an Efficient Self-Supporting Electrocatalyst for Ammonia Electrolysis Producing Hydrogen

Ammonia (NH₃) is one of the hydrogen carriers that has received extensive attention due to its high hydrogen content and carbon-free nature. The ammonia electro-oxidation reaction (AOR) and the liquid AOR (LAOR) are integral parts of an ammonia-based energy system. The exploration of low-cost and efficient electrocatalysts for the AOR and LAOR is very important but very difficult. In this work, a novel self-supporting AOR and LAOR bifunctional electrocatalyst of a Ag₃CuS₂ film is synthesized by a simple hydrothermal method. The Ag₃CuS₂ film without a substrate shows efficient catalytic activity and enhanced stability for NH₃ electrolysis in both aqueous ammonia solution and liquid ammonia, including an onset potential of 0.7 V for the AOR and an onset potential of 0.4 V for the LAOR. The density functional theory calculations prove that compared to Cu atoms, Ag atoms with appropriate charge density on the surface of Ag₃CuS₂ are more electrocatalytically active for NH₃ splitting, including the low energy barrier in the rate-determining *NH₃ dehydrogenation step and the spontaneous tendency in the N₂ desorption process. Overall, the foamed Ag₃CuS₂ film is one of prospective low-cost and stable electrocatalysts for the AOR and LAOR, and the self-supporting strategy without a substrate provides more perspectives to tailor more meaningful and powerful electrocatalysts.

Nickel phosphide on Ni foam as anode and peroxymonosulfate as the chemical oxidizer for effective direct urea fuel cell

The direct urea fuel cell (DUFC) is a low cost and competitive approach for contemporaneous urine or urea-contaminated wastewater treatment and electricity generation. However, the lack of efficient urea oxidation reaction (UOR) electrocatalysts and suitable electron acceptors remains a challenge for practical applications. Here, we developed a DUFC system using Ni₂P@Ni foam as the anode and peroxymonosulfate (PMS) as the chemical oxidizers. The Ni₂P@Ni foam anode showed a high oxidation activity for UOR with an onset potential of 0.30 V vs. Ag/AgCl and Tafel slope of 34.4 mV/dec. PMS with high theoretical potential improved the cell voltage to 1.43 V. A power density of DUFC up to 4.91 mW/cm² was achieved using PMS at room temperature, which was approximately twice as high as using H₂O₂ (2.38 mW/cm²). Ni^II/Ni^III was the redox active species on the Ni₂P anode in the DUFC process, and Ni^II was electrochemically oxidized to Ni^III, which reverted to Ni^II by urea reduction. When real human urine was used as the fuel, a power density of 4.46 mW/cm² can be achieved at room temperature. This DUFC with high cell performance showed potential application in urea wastewater treatment.

Density Functional Theory Investigation of the NiO@Graphene Composite as a Urea Oxidation Catalyst in the Alkaline Electrolyte

Developing efficient and low-cost urea oxidation reaction (UOR) catalysts is a promising but still challenging task for environment and energy conversion technologies such as wastewater remediation and urea electrolysis. In this work, NiO nanoparticles that incorporated graphene as the NiO@Graphene composite were constructed to study the UOR process in terms of density functional theory. The single-atom model, which differed from the previous heterojunction model, was employed for the adsorption/desorption of urea and CO2 in the alkaline media. As demonstrated from the calculated results, NiO@Graphene prefers to adsorb the hydroxyl group than urea in the initial stage due to the stronger adsorption energy of the hydroxyl group. After NiOOH@Graphene was formed in the alkaline electrolyte, it presents excellent desorption energy of CO2 in the rate-determining step. Electronic density difference and the d band center diagram further confirmed that the Ni(III) species is the most favorable site for urea oxidation while facilitating charge transfer between urea and NiO@Graphene. Moreover, graphene provides a large surface for the incorporation of NiO nanoparticles, enhancing the electron transfer between NiOOH and graphene and promoting the mass transport in the alkaline electrolyte. Notably, this work provides theoretical guidance for the electrochemical urea oxidation work.

Electrooxidation of Urea in Alkaline Solution Using Nickel Hydroxide Activated Carbon Paper Electrodeposited from DMSO Solution

Electrooxidation of urea plays a substantial role in the elimination of urea-containing wastewater and industrial urea. Here, we report the electrodeposition of nickel hydroxide catalyst on commercial carbon paper (CP) electrodes from dimethyl sulphoxide solvent (Ni(OH)2-DMSO/CP) for urea electrooxidation under alkaline conditions. The physicochemical features of Ni(OH)2-DMSO/CP catalysts using scanning electron microscopy and X-ray photoelectron spectroscopy revealed that the Ni(OH)2-DMSO/CP catalyst shows nanoparticle features, with loading of <1 wt%. The cyclic voltammetry and electrochemical impedance spectroscopy revealed that the Ni(OH)2-DMSO/CP electrode has a urea oxidation onset potential of 0.33 V vs. Ag/AgCl and superior electrocatalytic performance, which is a more than 2-fold higher activity in comparison with the counterpart Ni(OH)2 catalyst prepared from the aqueous electrolyte. As expected, the enhancement in electrocatalytic activity towards urea was associated with the superficial enrichment in the electrochemically active surface area of the Ni(OH)2-DMSO/CP electrodes. The results might be a promising way to activate commercial carbon paper with efficient transition metal electrocatalysts, for urea electrooxidation uses in sustainable energy systems, and for relieving water contamination.

Superior catalytic activity of α-Ni(OH)2 for urea electrolysis

α-Ni(OH)₂ exhibits a higher intrinsic UOR catalytic activity and durable stability in comparison with its nickel hydroxide counterpart β-Ni(OH)₂.

Construction of self-supporting bimetallic sulfide arrays as a highly efficient electrocatalyst for bifunctional electro-oxidation

Bimetal nickel–cobalt sulfide nanosheets grown on nickel foam (NCS/NF) exhibit superior OER and UOR activities with low potentials of 1.46 and 1.31 V at 10 mA cm−2, and even good activity in alkaline water electrolytes.

Novel Bifunctional V2O3 Nanosheets Coupled with N-Doped-Carbon Encapsulated Ni Heterostructure for Enhanced Electrocatalytic Oxidation of Urea-Rich Wastewater

Developing high performance bifunctional transition metal catalysts would be significantly beneficial for electrocatalytic oxidation of urea-rich wastewater. Herein, we synthesize a V₂O₃ nanosheet anchored N-doped-carbon encapsulated Ni heterostructure (Ni@C-V₂O₃/NF) for the reactions of urea oxidation (UOR) and hydrogen evolution (HER). Electrochemical results indicate that it exhibits small potentials of 1.32, 1.39, and 1.43 V for UOR and low overpotentials of 36, 254, and 355 mV for HER at ±10, ± 500 and ±1000 mA cm^-2, respectively. It can work at 100 mA cm^-2 for over 72 h as cathode and anode electrode without obvious attenuation, suggesting an outstanding durability. The reason for this behavior could be ascribed to the N-doped-carbon coating structure, the synergetic effects between Ni and V₂O₃, and the nano/micro nanosheets architecture self-supported on nickel foam. This work could provide a promising, inexpensive, and green method for the degradation of urea-rich wastewater and hydrogen production.

Ir-Doped Ni-based metal–organic framework ultrathin nanosheets on Ni foam for enhanced urea electro-oxidation

NiIr-based metal–organic frameworks grown on a nickel foam substrate (NiIr-MOF/NF) are synthesized by a solvothermal method and directly used for urea electro-oxidation.

Recent Progress on Irradiation-Induced Defect Engineering of Two-Dimensional 2H-MoS2 Few Layers

Atom-thick two-dimensional materials usually possess unique properties compared to their bulk counterparts. Their properties are significantly affected by defects, which could be uncontrollably introduced by irradiation. The effects of electromagnetic irradiation and particle irradiation on 2H MoS 2 two-dimensional nanolayers are reviewed in this paper, covering heavy ions, protons, electrons, gamma rays, X-rays, ultraviolet light, terahertz, and infrared irradiation. Various defects in MoS 2 layers were created by the defect engineering. Here we focus on their influence on the structural, electronic, catalytic, and magnetic performance of the 2D materials. Additionally, irradiation-induced doping is discussed and involved.