Operando XAFS study of carbon supported Ni, NiZn, and Co catalysts for hydrazine electrooxidation for use in anion exchange membrane fuel cells

Electrodegradation of nitrogenous pollutants in sewage: from reaction fundamentals to energy valorization applications

The excessive accumulation of nitrogen pollutants (mainly nitrate, nitrite, ammonia nitrogen, hydrazine, and urea) in water bodies seriously disrupts the natural nitrogen cycle and poses a significant threat to human life and health. Electrolysis is considered a promising method to degrade these nitrogenous pollutants in sewage, with the advantages of high efficiency, wide generality, easy operability, retrievability, and environmental friendliness. For particular energy devices, including metal-nitrate batteries, direct fuel cells, and hybrid water electrolyzers, the realization of energy valorization from sewage purification processes (e.g., valuable chemical generation, electricity output, and hydrogen production) becomes feasible. Despite the progress in the research on pollutant electrodegradation, the development of electrocatalysts with high activity, stability, and selectivity for pollutant removal, coupled with corresponding energy devices, remains a challenge. This review comprehensively provides advanced insights into the electrodegradation processes of nitrogenous pollutants and relevant energy valorization strategies, focusing on the reaction mechanisms, activity descriptors, electrocatalyst design, and actuated electrodes and operation parameters of tailored energy conversion devices. A feasibility analysis of electrodegradation on real wastewater samples from the perspective of pollutant concentration, pollutant accumulation, and electrolyte effects is provided. Challenges and prospects for the future development of electrodegradation systems are also discussed in detail to bridge the gap between experimental trials and commercial applications.

Ru-Ni nanoparticles electrodeposited on rGO/Ni foam as a binder-free, stable and high-performance anode catalyst for direct hydrazine fuel cell

Bimetallic Ru-Ni nanoparticles was synthesized on the reduced graphene oxide decorated Ni foam (Ru-Ni/rGO/NF) by electroplating method to be utilized as the anode electrocatalyst for direct hydrazine-hydrogen peroxide fuel cells (DHzHPFCs). The synthesized electrocatalysts were characterized by X-ray diffraction, Field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The electrochemical properties of catalysts towards hydrazine oxidation reaction in an alkaline medium were evaluated by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. In the case of Ru1-Ni3/rGO/NF electrocatalyst, Ru1-Ni3 provided active sites due to low activation energy (22.24 kJ mol-1) for hydrazine oxidation reaction and reduced graphene oxide facilitated charge transfer by increasing electroactive surface area (EASA = 677.5 cm2) with the small charge transfer resistance (0.1 Ω cm2). The CV curves showed that hydrazine oxidation on the synthesized electrocatalysts was a first-order reaction in low concentrations of N2H4 and the number of exchanged electrons was 3.0. In the single cell of the of direct hydrazine-hydrogen peroxide fuel cell, the maximum power density value of Ru1-Ni3/rGO/NF electrocatalyst was 206 mW cm-2 and the open circuit voltage was 1.73 V at 55 °C. These results proved that the Ru1-Ni3/rGO/NF is a promising candidate for using as the free-binder anode electrocatalyst in the future application of direct hydrazine-hydrogen peroxide fuel cells due to its excellent structural stability, ease of synthesis, low cost, and high catalytic performance.

Understanding hydrazine oxidation electrocatalysis on undoped carbon

Carbons are ubiquitous electrocatalytic supports for various energy-related transformations, especially in fuel cells. Doped carbons such as Fe-N-C materials are particularly active towards the oxidation of hydrazine, an alternative fuel and hydrogen carrier. However, there is little discussion of the electrocatalytic role of the most abundant component - the carbon matrix - towards the hydrazine oxidation reaction (HzOR). We present a systematic investigation of undoped graphitic carbons towards the HzOR in alkaline electrolyte. Using highly oriented pyrolytic graphite electrodes, as well as graphite powders enriched in either basal planes or edge defects, we demonstrate that edge defects are the most active catalytic sites during hydrazine oxidation electrocatalysis. Theoretical DFT calculations support and explain the mechanism of HzOR on carbon edges, identifying unsaturated graphene armchair defects as the most likely active sites. Finally, these findings explain the 'double peak' voltammetric feature observed on many doped carbons during the HzOR.

Ultrathin NiSe Nanosheets on Ni Foam for Efficient and Durable Hydrazine-Assisted Electrolytic Hydrogen Production

Hydrazine-assisted electrochemical water splitting is an important avenue toward low cost and sustainable hydrogen production. An efficient and stable bifunctional electrocatalyst for the hydrogen evolution reaction (HER) and the anodic hydrazine oxidation reaction (HzOR) is fundamental to this goal. Herein, we employed a facile method to fabricate ultrathin NiSe nanosheet arrays on nickel foam (NiSe/NF), which exhibits predominant electrocatalytic activity for both HER and HzOR. Our investigations revealed that the excellent electrocatalytic activity of the NiSe/NF mainly arises from the abundant electrocatalytic active sites endowed by the ultrathin nanosheet morphology, the rugged feature of the extended (100) nanosheet surface, the rich presence of Se on the nanosheet surface, and the three-dimensional (3D) porous structure of the NF and other factors such as high conductivity of the NiSe/NF and strong NiSe-NF adhesion. We assembled a hydrazine-boosted electrochemical water splitting cell using NiSe/NF as a bifunctional catalyst for both of the electrodes, and the constructed cell exhibits an ultralow overpotential (310 mV at 10 mA cm^-2), which is robust for 30 h continuous electrolysis in a 1 M KOH electrolyte. This work provides a promising avenue toward low cost, high-efficiency, and stable hydrogen production based on hydrazine-assisted electrolytic water splitting for future.

Fabrication of an ultra-sensitive para-nitrophenol sensor based on facile Zn-doped Er2O3 nanocomposites via an electrochemical approach

In this study, a semiconductor-doped nanocomposite material (Zn-doped Er2O3 nano-composites) was prepared via a single-step wet-chemical technique at alkaline pH. Fourier-transform infrared spectroscopy (FT-IR), UV/Vis spectroscopy, photoluminescence spectroscopy (PL), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (XEDS), and X-ray powder diffractometry (XRD) were applied to determine the structural and morphological properties of the Zn-doped Er2O3 nanocomposite. A thin layer of aggregated Zn-doped Er2O3 nanocomposite was fabricated on the flat surface of a glassy carbon electrode (GCE) with 5% ethanolic Nafion as conducting coating binder for the development of a selective and sensitive p-nitrophenol (para-NP) capturing electrochemical probe for environmental remediation. After the fabrication of the sensor, a novel current-potential (I-V) electrochemical approach was applied to determine its selectivity and sensitivity together with all the necessary analytical parameters against para-NP. Moreover, the calibration plot was found to be linear with the linear dynamic range (LDR) of para-NP concentration. The limit of detection (LOD) at a signal-to-noise ratio of 3 (S/N ∼ 3) and sensitivity were also calculated to be 0.033 ± 0.002 pM and 28.481 × 10-2 μA μM-1 cm-2, respectively, based on the gradient of the calibration plot, and the limit of quantification (LOQ) was determined to be 0.11 ± 0.02 pM. This work demonstrates a well-known approach for the first time that can be used for the development of efficient electrochemical sensors. These sensors based on semiconductor doped nanomaterials embedded onto the GCE for the detection of toxic chemicals in an aqueous system as an environmental remediation. It can be further applied for the analysis of real environmental samples and in the healthcare field.

Development of 3-methoxyaniline sensor probe based on thin Ag2O@La2O3 nanosheets for environmental safety

An electrochemical sensor based on glassy carbon electrode modified by Ag₂O@La₂O₃ nanosheets with 5% ethanolic nafion as conducting binder was developed for the selective and ultra-sensitive determination of 3-methoxyanaline in the presence of other interfering toxic chemicals in aqueous system by electrochemical approach for the first time.

The morphology-dependent electrocatalytic activities of spinel-cobalt oxide nanomaterials for direct hydrazine fuel cell application

Morphologically-tuned spinel-cobalt oxide nanomaterials such as pellet-, flower-, cube- and sheet-like structures as an anode for an enhanced hydrazine oxidation reaction (HOR) is demonstrated.

Sensitive 3-chlorophenol sensor development based on facile Er2O3/CuO nanomaterials for environmental safety

Low-dimensional Er₂O₃/CuO nanomaterials were synthesized by wet-chemical process and totally characterized with various conventional methods. The electrochemical approach could be a pioneer development in selective 3-CP sensor development using doped nano-structural materials by an electrochemical method for the various phenolic sensor applications for environmental safety in broad scales.

Local Fine Structural Insight into Mechanism of Electrochemical Passivation of Titanium

Electrochemically formed passive film on titanium in 1.0 M H2SO4 solution and its thickness, composition, chemical state, and local fine structure are examined by Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure. AES analysis reveals that the thickness and composition of oxide film are proportional to the reciprocal of current density in potentiodynamic polarization. XPS depth profiles of the chemical states of titanium exhibit the coexistence of various valences cations in the surface. Quantitative X-ray absorption near edge structure analysis of the local electronic structure of the topmost surface (∼5.0 nm) shows that the ratio of [TiO2]/[Ti2O3] is consistent with that of passivation/dissolution of electrochemical activity. Theoretical calculation and analysis of extended X-ray absorption fine structure spectra at Ti K-edge indicate that both the structures of passivation and dissolution are distorted caused by the appearance of two different sites of Ti-O and Ti-Ti. And the bound water in the topmost surface plays a vital role in structural disorder confirmed by XPS. Overall, the increase of average Ti-O coordination causes the electrochemical passivation, and the dissolution is due to the decrease of average Ti-Ti coordination. The structural variations of passivation in coordination number and interatomic distance are in good agreement with the prediction of point defect model.

A 3D porous Ni-Cu alloy film for high-performance hydrazine electrooxidation

Structural design and catalyst screening are two most important factors for achieving exceptional electrocatalytic performance. Herein we demonstrate that constructing a three-dimensional (3D) porous Ni-Cu alloy film is greatly beneficial for improving the hydrazine oxidation reaction (HzOR) performance. A facile electrodeposition process is employed to synthesize a Ni-Cu alloy film with a 3D hierarchical porous structure. As an integrated electrode for HzOR, the Ni-Cu alloy film exhibits superior catalytic activity and stability to the Ni or Cu counterparts. The synthesis parameters are also systematically tuned for optimizing the HzOR performance. The excellent HzOR performance of the Ni-Cu alloy film is attributed to its high intrinsic activity, large electrochemical specific surface area, and 3D porous architecture which offers a "superaerophobic" surface to effectively remove the gas product in a small volume. It is believed that the Ni-Cu alloy film electrode has potential application in direct hydrazine fuel cells as well as other catalytic fields.

Ultrasensitive and selective hydrazine sensor development based on Sn/ZnO nanoparticles

Fabrication of highly sensitive (∼5.0108 μA cm⁻² μM⁻¹) and selective hydrazine chemical sensor based on wet-chemically prepared Sn/ZnO nanoparticles deposited glassy carbon electrodes with a detection limit as low as 18.95 ± 0.02 pM (at an S/N of 3).