Heterostructured Nickel‐Cobalt Selenide Immobilized onto Porous Carbon Frameworks as an Advanced Anode Material for Urea Electrocatalysis

Urea catalytic oxidation for energy and environmental applications

Urea is one of the most essential reactive nitrogen species in the nitrogen cycle and plays an indispensable role in the water-energy-food nexus. However, untreated urea or urine wastewater causes severe environmental pollution and threatens human health. Electrocatalytic and photo(electro)catalytic urea oxidation technologies under mild conditions have become promising methods for energy recovery and environmental remediation. An in-depth understanding of the reaction mechanisms of the urea oxidation reaction (UOR) is important to design efficient electrocatalysts/photo(electro)catalysts for these technologies. This review provides a critical appraisal of the recent advances in the UOR by means of both electrocatalysis and photo(electro)catalysis, aiming to comprehensively assess this emerging field from fundamentals and materials, to practical applications. The emphasis of this review is on the design and development strategies for electrocatalysts/photo(electro)catalysts based on reaction pathways. Meanwhile, the UOR in natural urine is discussed, focusing on the influence of impurity ions. A particular emphasis is placed on the application of the UOR in energy and environmental fields, such as hydrogen production by urea electrolysis, urea fuel cells, and urea/urine wastewater remediation. Finally, future directions, prospects, and remaining challenges are discussed for this emerging research field. This critical review significantly increases the understanding of current progress in urea conversion and the development of a sustainable nitrogen economy.

A novel sacrificial solvent method to synthesize self-supporting Co9S8/Ni3S2 heterostructure catalyst for efficient oxygen evolution reaction

Synthesizing catalysts for efficient oxygen evolution reaction (OER) with lower cost and simpler design is of significant importance to achieve sustainable hydrogen production. In this work, we propose a novel "sacrificial solvent method" for the first time. Dicobalt octacarbonyl (Co2(CO)8), dimethyl sulfoxide (DMSO), and Ni foam (NF) were used as the raw materials in the solvothermal process. DMSO played the role of both the sacrificial solvent and the sulfur source. Through the self-consumption of DMSO, we finally obtained the Co9S8/Ni3S2 heterostructure supported on the NF (Co9S8/Ni3S2@NF) in one step. The Co9S8/Ni3S2@NF catalyst exhibited excellent OER activity in alkaline environment, with an overpotential of only 264 mV at a current density of 20 mA cm-2, a low Tafel slope of 68.28 mV dec-1 and maintained its current density after 20 h of constant potential testing. This work introduces a new method for synthesizing metal sulfide catalysts using DMSO as a sacrificial solvent. It provides broader opportunities for the development of more efficient and sustainable catalysts for energy conversion and storage.

Bi-Fe chalcogenides anchored carbon matrix and structured core-shell Bi-Fe-P@Ni-P nanoarchitectures with appealing performances for supercapacitors

Pseudocapacitive materials based on multi-active components are attractive platforms for future portable energy devices due to their excellent redox processes and low cost. In this study, nanostructured bismuth-iron chalcogenide anchored on multiwalled carbon nanotube framework (Bi-Fe chalcogenide/C)-based electrode materials were fabricated via a simple solvothermal protocol with enhanced electrochemical performances. The obtained Bi-Fe chalcogenide/C nanocomposites combining the improved electroconductivity of carbonic frameworks and high pseudocapacitive properties of Bi/Fe reversible redox processes were employed as negative electrodes for asymmetric supercapacitor (ASC) devices. Systematic investigation of the synthesized materials and capacitive performance indicated that the Bi-Fe-P/C electrode simultaneously achieved an intrinsically appreciable specific capacitance of 532 F g^-1 at a current density of 1 A g^-1, high-rate capability, and cyclic stability, profiting from the structural and amorphous merits as well as the collaborative effect of multiple components. Besides, we employed an effective strategy to graft Bi-Fe-P film on a self-standing nickel phosphide (Ni-P) to manufacture a cathode with superior capacitive performances. The as-prepared core-shell Bi-Fe-P@Ni-P was used as a high-performance positive electrode and displayed a large specific capacitance of 230.6 mAh g^-1 at 1 A g^-1. Additionally, we also assembled an ASC system using the core-shell Bi-Fe-P@Ni-P as a positive electrode and amorphous Bi-Fe-P/C as a negative electrode with an expanded operational potential of 1.6 V. The hybrid device delivered a high specific energy density of 81.5 Wh kg^-1 at a power density of 890.2 W kg^-1 together with good cyclic characteristics (85.6% capacitance retention after 8000 consecutive cycles). The obtained findings offer new insights into the design of advanced energy storage materials at relatively low costs and underscore the proficiency of heterostructured multicomponent electrodes as a practical option for enhancing the electrochemical performance of ASC.

Cobalt-modified 2D porous organic polymer for highly efficient electrocatalytic removal of toxic urea and nitrophenol

The urea oxidation reaction (UOR) and nitrophenol reduction are safe and key limiting reactions for sustainable energy conversion and storage. Urea and nitrophenol are abundant in industrial and agricultural wastes, human wastewater, and in the environment. Catalytic oxidative and reductive removal is the most effective process to remove urea and 4-nitrophenol from the environment, necessary to protect human health. 2D carbon-supported, cobalt nanoparticle-based materials are emerging catalysts for nitrophenol reduction and as an anode material for the UOR. In this work, cobalt modified on a porous organic polymer (CoPOP) was synthesized and carbonized at 400 and 600 °C. The formation of CoPOP was confirmed by FT-IR spectroscopy, the 2D graphitic layer and amorphous carbon with cobalt metal by TEM, SEM, and PXRD, and the elemental composition by TEM mapping, EDX, and XPS. The catalytic activity for the 4-nitrophenol reduction was studied and the related electrocatalytic UOR was scientifically evaluated. The catalytic activity toward the reduction of 4-NP to 4-AP was tested with the addition of NaBH₄; CoPOP-3 exhibited enhanced activity at a rate of 0.069 min^-1. Furthermore, LSV investigated the catalytic activity of materials toward UOR, producing hydrogen gas, the products of which were analyzed via gas chromatography. Among the electrocatalysts studied, CoPOP-2 exhibited a lower onset potential, and the Tafel slope was 1.34 V and 80 mV dec^-1. This study demonstrates that cobalt metal-doped porous organic polymers can be used as efficient catalysts to remove urea and nitrophenol from wastewater.

Synthesis of porous Ag2S-NiCo2S4 hollow architecture as effective electrode material with high capacitive performances

Fabrication of highly reactive and cost-effective electrode materials is a key to efficient functioning of green energy technologies. Decorating redox-active metal sulfides with conductive dopants is one of the most effective approaches to enhance electric conductivity and consequently boost capacitive properties. Herein, hierarchically hollow Ag₂S-NiCo₂S₄ architectures are designed with an enhanced conductivity by a simple solvothermal approach. With the favorable porous characteristics and composition, the optimized Ag₂S-NiCo₂S₄-5 electrode exhibits higher specific capacitance (276.5 mAh g^-1 at a current density of 1 A g^-1), a good rate performance (56.3% capacity retention at 50 A g^-1), and an improved cycling stability (92.4% retention after 2000 cycles). This finding originates from the enhanced charge transportation ability within the hierarchical structure, abundant electroactive sites, and low contact resistance. In addition, a battery supercapacitor device constructed with the Ag₂S-NiCo₂S₄-5 as a positive electrode displays a maximum energy density of 63.3Wh kg^-1 at an energy density of 821.8 W kg^-1 with an excellent cycling stability (89.4% capacity retention after 10 000 cycles). Therefore, the present work puts forward new possibility to develop composite electrodes for energy storage battery-supercapacitor.

Rational Design of Porous Structured Nickel Manganese Sulfides Hexagonal Sheets-in-Cage Structures as an Advanced Electrode Material for High-Performance Electrochemical Capacitors

The design of hierarchical electrodes comprising multiple components with a high electrical conductivity and a large specific surface area has been recognized as a feasible strategy to remarkably boost pseudocapacitors. Herein, we delineate hexagonal sheets-in-cage shaped nickel-manganese sulfides (Ni-Mn-S) with nanosized open spaces for supercapacitor applications to realize faster redox reactions and a lower charge-transfer resistance with a markedly enhanced specific capacitance. The hybrid was facilely prepared through a two-step hydrothermal method. Benefiting from the synergistic effect between Ni and Mn active sites with the improvement of both ionic and electric conductivity, the resulting Ni-Mn-S hybrid displays a high specific capacitance of 1664 F g^-1 at a current density of 1 A g^-1 and a capacitance of 785 F g^-1 is maintained at a current density of 50 A g^-1 , revealing an outstanding capacity and rate performance. The asymmetric supercapacitor device assembled with the Ni-Mn-S hexagonal sheets-in-cage as the positive electrode delivers a maximum energy density of 40.4 Wh kg^-1 at a power density of 750 W kg^-1 . Impressively, the cycling retention of the as-fabricated device after 10 000 cycles at a current density of 10 A g^-1 reaches 85.5 %. Thus, this hybrid with superior capacitive performance holds great potential as an effective charge-storage material.

Construction of a bimetallic nickel–cobalt selenide pompon used as a superior anode material for high performance sodium storage

Pompon-like NiCo₂Se₄ can effectively promote the penetration of an electrolyte, increase electron and ion diffusion channels, alleviate volume expansion and achieve excellent sodium storage performance.