Electrochemical Impedance Spectroscopy Characterization Research Articles

Tightly and abundantly contacted Z-scheme heterojunction of Bi-modified TiO2/BiOCl: In-situ construction and boosting visible-light-driven purification of liquor brewing wastewater

The lower specific surface area and limited surface contact between BiOCl and TiO2 in composite fabricated by hybridization of TiO2 with BiOCl extremely hinder its catalytic performance. In this work, the area of interface contact between BiOCl and TiO2 was increased through the mediation of SiO2, and a Bi-modified ternary 0D/2D/2D TiO2/BiOCl Z-scheme heterojunction photocatalyst with large specific surface area (= 237.83 m2g−1) and surface plasmon resonance (SPR) effect was constructed in situ by ingeniously utilizing the reduction of carbon species generated during the calcination process. The results show that the COD removal rate of Bi/TBOC-10% for real liquor brewing wastewater (LBW) reaches 90.5% after 10 hours of visible light irradiation, which is 2.6 times and 2.1 times that of TiO2 and Degussa P25, respectively. The COD removal rate of the composite was reduced only by 8.9% after five cycles of performance test (50 h). Photoluminescence spectroscopy (PL), Transient Photocurrent Response (TPR), Electrochemical Impedance Spectroscopy (EIS) and BET characterization suggest that its excellent photocatalytic activity should be attributed to the Z-scheme heterojunction that broadens the light absorption range while retains strong oxidation-reduction active sites, the SPR effect that facilitates the separation and migration of photogenerated carriers, and high specific surface area of the composite that provides more active sites for the photodegradation reaction.

Advancing corrosion protection in confined spaces: a solvent-free UV LED-curable coating for steel pipelines with enhanced barrier properties and harsh environment performance

AbstractThis study investigates a novel solvent-free, UV LED-curable coating as a robust corrosion protection solution for the inner surface of steel pipelines. The properties of the UV-cured film were characterized in terms of reactivity, thermomechanical properties, and adhesion to metal substrates. The coating was applied to the inside steel pipelines and cured using a patented UV LED lamp designed to fit in confined spaces. Finally, electrochemical impedance spectroscopy characterization and an accelerated cyclic electrochemical technique were performed on the coated pipes to study the corrosion protection properties of the coating, both with and without the addition of inorganic fillers. The results were compared to a commercially available thermally cured coating. It was found that the UV-cured coating confers high barrier properties, effectively preventing liquid penetration even under elevated temperature conditions. Furthermore, the corrosion protection performance in harsh environments was comparable to and, in some cases, higher than standard epoxy linings.

Synergy of Active Sites and Charge Transfer in Branched WO3/W18O49 Heterostructures for Enhanced NO2 Sensing.

Achieving reliable detection of trace levels of NO2 gas is essential for environmental monitoring and protection of human health protection. Herein, a thin-film gas sensor based on branched WO3/W18O49 heterostructures was fabricated. The optimized WO3/W18O49 sensor exhibited outstanding NO2 sensing properties with an ultrahigh response value (1038) and low detection limit (10 ppb) at 50 °C. Such excellent sensing performance could be ascribed to the synergistic effect of accelerated charge transfer and increased active sites, which is confirmed by electrochemical impedance spectroscopy and temperature-programmed desorption characterization. The sensor exhibited an excellent detection ability to NO2 under different air quality conditions. This work provides an effective strategy for constructing WO3/W18O49 heterostructures for developing NO2 gas sensors with an excellent sensing performance.

Direct Recycling of β‐Li3PS4‐Based All‐Solid‐State Li‐Ion Batteries: Interactions of Electrode Materials and Electrolyte in a Dissolution‐Based Separation Process

All‐solid‐state batteries (ASSB) are currently developed at high pace and show a strong potential for market introduction within the next years. Though their performance has improved considerably over the last years, investigation of their sustainability and the development of suitable recycling strategies have received less attention. However, their potential for efficient circular processes must be accessed comprehensively. In this article, the separation of the solid electrolyte β‐Li3PS4 from different lithium transition metal oxide electrode materials (LiCoO2, LiMn2O4, LiNi0.8Mn0.1Co0.1O2, LiFePO4, LiNi0.8Co0.15Al0.05O2, and Li4Ti5O12) are investigated via an approach based on the dissolution and subsequent precipitation of the thiophosphate using N‐methylformamide as solvent. A combination of X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, inductively coupled plasma mass spectrometry, iodometric titration, and X‐ray photoelectron spectroscopy as well as electrochemical impedance spectroscopy and electrochemical characterization is used to characterize the electrolyte and electrode materials before and after separation. Herein, it is found that the presence of electrode materials in the dissolution process can lead to significant chemical reactions. These interactions can (but most not) lead to strong alteration of the electrochemical characteristics of the individual compounds. Thus, it is shown that an efficient recovery of materials likely depends on the precise material combination within an ASSB.

Optimization of the Electrochemical Nature of Ni/Co MOF Assisted by Zn Metal Centres for Better Electrode Performance in Hybrid Devices

Owing to the exceptional porous coordination chemistry and expanded redox culture of mixed metal organic framework (MMOF) materials are now presenting a hot matter for their potential usage in battery-supercapacitor electrodes. Here, we synthesized Ni/Co-MOF and its based Zn x -(Ni/Co)y-MOF nanoparticles containing different transition metals ratio; x: y = 0.25:0.75, 0.50:0.50, and 0.75:0.25 by hydrothermal process and named as ZMOF1, ZMOF2 and ZMOF3. Their electrochemical profile was carried out by CV, GCD and EIS characterization in three electrode setup. Among the MOFs nanoparticles, partially Zn enriched ZMOF1 shows prominent specific capacity of 177.23 and 181.12 C g−1 in 1.0 and 3.0 M KOH electrolyte solution at current density of 0.3 A g−1 along with good rate capability performance. Meanwhile, it retains brilliant specific capacity ∼ 86% of its original value compared to other displayed by ZMOF2 and ZMOF3 (80% and 69%) after charging-discharging for 3000 cycles at j = 4.0 A g−1. Moreover, modified power law was utilized to estimate the battery-type charge storage worth of ZMOF1 from CV cycle (at 5 mV s−1) in 1.0 and 3.0 M electrolytes medium thereby found the contribution 91.58% and 94.32%, respectively. These features of ZMOF1 attributed to particle diverse morphology, enriched redox sites and admiring electrical conductivity.

Alcohol splitting with bipolar membranes for the production of metal alkoxides: Alcohol splitting behaviour and ion transport kinetics

In this study, an electrochemical route was proposed for metal alkoxides preparation by taking advantage of alcohol dissociation (ROH → RO− + H+) in a bipolar membrane. A current density of 25 mA cm−2 was optimized for lithium methoxide and magnesium methoxide production with energy consumption of 28.84 kWh∙kg−1 and 27.98 kWh∙kg−1, respectively. Electrochemical impedance spectroscopy (EIS) characterization indicated that the threshold voltage for alcohol dissociation for the Neosepta BP-1E bipolar membrane is 6.02 V, which is much higher than that for water splitting of 0.72 V. For a bipolar membrane, the resistance of the alcohol dissociation (RAD) and the resistance of the diffusion boundary layer (RDBL) are the major contributors to the impedance for methanol splitting, while only the latter is the predominant contributor to the impedance for water splitting. Overall, alcohol splitting in bipolar membrane provides a versatile platform for green preparation of metal alkoxides.

Localized Corrosion and Passive Film Characteristics of Additive Vs. Wrought Al-Zn-Mg-Cu-Based Alloy

Al-Zn-Mg-Cu alloys of the 7xxx series have proven to be excellent candidates for the aerospace, defense, and automotive industries due to their high strength to weight ratio, high corrosion resistance, and fatigue performance. For additively manufactured alloys manufactured using laser powder bed fusion (LPBF), the non-conventional microstructures formed as a result of one or more factors like alloy modification, LPBF process, and subsequent thermal treatments can lead to change in corrosion behavior and mechanisms.Using scanning vibrating electrode technique (SVET) and immersion tests in chloride environments, this work concentrates on understanding the localized corrosion behavior of additively manufactured Al-Zn-Mg-Cu based alloy in comparison with its wrought counterpart. To understand the corrosion mechanisms, microstructures including the precipitates are characterized at different length scales using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and correlated with the corrosion behavior. The difference in passive film characteristics of additive vs. wrought Al-Zn-Mg-Cu based alloy is studied using electrochemical impedance spectroscopy (EIS) and X-Ray photoelectron spectroscopy (XPS) characterization. Overall, the LPBF-based alloy studied shows better corrosion performance than the wrought counterpart in chloride environments. The microstructural differences and mechanisms responsible for this behavior is proposed.

Metal Composite Nano-Catalyst Enhanced Solid Oxide Fuel Cell Anodes for Improved Performance and Stability with Hydrocarbon Containing Fuels

Implementation of nano-catalyst materials into solid oxide fuel cell (SOFC) electrodes to improve performance and stability has been widely studied. Addition of the nano-catalysts into an electrode structure serves to enhance the electrochemical performance of the SOFC by increasing the Triple Phase Boundary (TPB) area, improving redox stabilization, and modifying reaction kinetics of hydrocarbon gasses that cause anode degradation due to carbon deposition.SOFCs operating upstream of a reformer need to exhibit good tolerance to any hydrocarbon components that may make their way to the stack. Typical Ni-based cermet anodes suffer from anode deactivation due to carbon build up under hydrocarbon flows. Carbon builds up and covers the TPB area which results in poor electrochemical performance. Larger carbon deposits can block pores within the anode microstructure which leads to gas diffusion issues. Carbon buildup also causes mechanical stresses to the electrode due to volumetric changes which can lead to fracture and complete failure of the cell.This work studied nano-catalyst decoration of the Ni-based cermet anodes with catalysts that promote internal reforming to protect against coking. Addition of active metal components (such as Co, Ge, Sn), and ceramic reforming promoters (such as CeO2, MgO) were investigated. Multi-component systems with several catalysts were also examined.Uniform incorporation of nano-catalyst into the anode microstructure was achieved through a patented liquid phase surfactant assisted process (using various catechol surfactants). Deposition loading densities and distribution of nanoparticles was controlled by altering the surfactant and catalyst solution concentrations.Nano-catalyst depositions were characterized through Scanning Electron Microscope (SEM) for imaging, Atomic Force Microscopy (AFM) for topographical analysis, and Energy-Dispersive X-ray Spectroscopy (EDS) for chemical characterization. Figure 1 shows SEM imaging of nano catalyst distribution of cerium oxide (CeO2) and cobalt oxide (CoO) co-deposition within an anode structure. A uniform distribution of nano-sized catalyst materials is observed.Accelerated evaluation of nano-catalysts for SOFCs was completed through symmetrical anode tests, where a symmetrical anode cell was subjected to hydrocarbon impurity at SOFC operating temperatures and electrochemical impedance spectroscopy (EIS) characterization was done over time. The best catalyst systems were down selected and long-term SOFC tests were completed with current-voltage-power (I-V-P) and EIS evaluation. Post-mortem microstructure and chemistry characterizations were also used in analysis.Uniform nano catalyst distribution of CeO2 and CoO within the anode structure demonstrated greater than 50% sustained improvement in harsh environment, long-term tests where the cell was subjected to 40% CH4 for 50+ h. Figure 1

Defect engineered efficient catalytic transfer hydrogenation of furfural to furfuryl alcohol in ethanol by Co-doped LaMnO3

As energy and CO2 concerns have become important aspects of scientific research, researchers are focusing on the development of alternative and green energies. Biomass is a significant energy source due to its cyclic utilization process and ability to renew CO2. The catalytic transfer hydrogenation (CTH) of sugar-derived furfural (FF) into furfuryl alcohol (FA) has attracted increasing attention; however, designing and synthesizing efficient nonnoble catalysts remains challenging. In this work, an oxygen defect-abundant LaMnO3 perovskite (R-LM4C-3h) was synthesized by combining the advantages of both Co heteroatom doping and H2 reduction. Raman, O2 temperature programmed desorption (O2-TPD), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and electrochemical impedance spectroscopy (EIS) characterizations revealed that R-LM4C-3h exhibited abundant oxygen defects that improved its electronic properties. As a result, adsorption ability for FF was enhanced, the reaction energy barrier was decreased, and CTH catalytic activity was promoted. A 93.6 mol% FA yield with 100 % FF conversion was achieved using ethanol as the hydrogen source. The oxygen defect-mediated catalyst also exhibited excellent stability with almost no activity reduction after 5 cycles. This surface reconstruction strategy for obtaining perovskites by fabricating abundant oxygen defects provides a superior opportunity to better explore the structure–function relationship of catalysts and develop efficient nonnoble metal-based catalysts.

Inter- and intra-molecular synergism in designing MgO-MCC composite-based coating: An efficient inhibitor for excellent anticorrosion performance

Polymer-based corrosion inhibitors are characterized by high efficiency, low cost, and eco-friendliness; however, their underlying mechanisms and modes of action remain poorly understood, presenting a significant challenge in optimizing their performance and effectiveness in practical applications. In this study, we successfully synthesized and thoroughly characterized a novel nanocomposite, combining magnesium oxide (MgO) nanoparticles with microcrystalline cellulose (MCC), and assessed its potential as a corrosion inhibitor for XC18 steel in an HCl 1.0 mol/L environment. The anticorrosive performance of the MgO-MCC composite for XC18 steel under harsh acidic conditions were investigated via electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), and surface characterization with a scanning electron microscope (SEM). Morphological analysis suggested the formation of a protective barrier with a fiber-like architecture on the XC18 surface that hindered corrosion. The electrochemical results revealed an increased inhibition performance of MgO-MCC with increasing concentrations reaching a higher efficiency of 87% at 700 ppm. Also, EIS results displayed maximum corrosion resistance achievement in the presence of MgO-MCC-based material (about 147.50 Ω cm2) along with mixed protection mechanism. Advanced theoretical calculations based on density functional theory (DFT) and first-principles density-functional tight-binding (DFTB) were performed to understand the MgO-MCC behavior at metal interface as well as to explore the inter- and intra- molecular interactions involved in the hybrid material formation, complementing the experimental findings. The interfacial mechanism and structure engineering of MgO-MCC composite for functionalizing the surface of metal alloy were also investigated and discussed. MgO-MCC benefits from essential inter and intra-molecular interactions, leading to a robust adsorption layer. The parallel adsorption configuration and mutual interaction establish a stable hierarchical self-assembly structure and stabilize the Fe―O bonds, thus improving the chemical and physical bonding with XC18 steel surface. The results suggest that the synergistic combination of MgO nanoparticles and polar-rich MCC is a valuable approach for designing novel hybrid materials.

Different carbonization temperature effect on Mo2C/MWCNT hybrid structure formation for enhanced supercapacitor performance

Various forms of energy used in our daily lives prevail in contemporary society. Application requirements have expanded from high power density to sustainable long term energy density for energy storage devices. The present study signifies effect of carbonization temperature role (700 °C, 800 °C, 900 °C) on electrochemical studies of MoO3 as electrode in supercapacitor devices. The prepared electrodes were characterized by electrochemical studies such as cyclic voltammetry (CV), galvanostatic charge discharge (GCD) and electrochemical impedance spectroscopy (EIS) and basic characterizations like X-ray diffraction, Raman, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM). Different carbonization temperatures with the addition of carbon precursors produced MoO2/MWCNT and α-Mo2C/MWCNT. The areal capacitance of MoO2–700 °C, MoO2–800 °C, α-Mo2C-900 °C electrode were found to be delivered as 0.45 F/cm2, 0.54 F/cm2, 0.96 F/cm2 at 0.003 A/cm2. The substantial increase in specific capacitance for α-Mo2C-900 °C was attributed to improve charge transport, faradic redox development occurring at electrode surface, and high electrical conductivity of carbon nanotubes.

Effect of Surface Defect Engineering on Proton Conductivity in Yttrium-Doped Barium Zirconate Thin Films

Yttrium-doped barium zirconate (BZY) has been considered as a potential electrolyte candidate for intermediate-to-low temperature protonic ceramic fuel cell applications. However, the transport properties of BZY are often limited by the formation of highly resistive space charge zones at lattice discontinuities, such as lattice defects and surfaces. Unlike lattice defects, how to reduce the space charge effects at surfaces remains less explored. In this regard, surface defect engineering can be a meaningful way to regulate the proton transport of BZY by tailoring the space charge distribution close to the surface. Here, the Ar and/or O2 plasma was used to prepare BZY thin films with different levels of surface defects. The results of electrochemical impedance spectroscopy and detailed structural characterization suggest that the plasma treatment is effective in improving the proton conductivities and lowering the activation energy of BZY thin films through the generation of negatively charged barium vacancy defects and the enrichment of yttrium dopants on the surface.

3D porous carbon nitride composited oxygen vacancy‐induced indium oxide for high photocatalytic nitrogen fixation on the interfacial surface

Semiconductor photocatalysis can utilize solar energy for clean energy conversion, but the catalytic efficiency is often unsatisfactory due to limited photo response and efficient separation of photogenerated carriers. In this work, 3D porous carbon nitride (3DPCN) composited oxygen vacancy‐induced indium oxide (3DPCN/VO‐In2O3) was successfully prepared and analyzed by some characterization methods. Meanwhile, the performance of photocatalytic nitrogen fixation was further investigated. X‐ray photoelectron spectroscopy and X‐Ray diffraction (XRD) confirmed the successful preparation of the composites and revealed the electron flow direction; scanning electron microscopy (SEM) and transmission electron microscopy showed the surface structure of the composites; diffuse reflectance spectroscopy and temperature programmed desorption (TPD) revealed the energy band position and adsorption mechanism; electron paramagnetic resonance (EPR) characterization confirms the successful construction of oxygen vacancies; and electrochemical impedance spectroscopy, photoluminescence, and other photochemical characterization results showed that 3DPCN/VO‐In2O3 band gap is narrower and more effective in capturing light than other materials, improving the photocatalytic nitrogen fixation ability. The test results show that the nitrogen fixation capacity of 3DPCN/VO‐In2O3 can reach a maximum value of 156 within 2 h. This result demonstrates that the modification of carbon nitride improves its nitrogen fixation effect, and the introduction of oxygen vacancy‐induced In2O3 improves the light absorption performance and is advantageous to the separation of photogenerated charge carriers.

Revealing mechanisms of activated carbon capacity fade in lithium-ion capacitors

The capacity fade mechanism of activated carbon (AC) electrode in Li-ion electrolyte was studied via electrochemical impedance spectroscopy (EIS) and post-mortem electrode characterizations at different stages of electrochemical cycling. Electrochemical cycling was conducted in half cells incorporating the AC working electrode, Li metal counter electrode, and 1 M LiPF6 in EC:DMC (1:1) electrolyte. Three phases were identified during the ageing process that corresponded with transformation of the passivation layer at the electrode surface and charge transfer impedance derived from the EIS analysis. Surface area and morphology analysis showed that the AC surface was progressively transformed by degradation products that reduced the available surface area and accessibility of electrolyte moieties into the pores. X-ray photoelectron spectroscopy suggested that the degradation products are from the LiPF6 salt decomposition and carbonate solvent decomposition, while Raman analysis demonstrated increased defects in the electrode as cycling progressed. The capacity fade was therefore caused by the synergistic effect of electrolyte degradation and active material transformation.

Determination of Nicotine in Human Saliva Using Electrochemical Sensor Modified with Green Synthesized Silver Nanoparticles Using Phyllanthus reticulatus Fruit Extract

In this study, for the first time, Phyllanthus Reticulatus fruit extract was utilized as a reducing agent in the synthesis of silver nanoparticles (Ag-NPs). For sample analysis, a number of approaches were employed. The synthesized Ag-NPs have a spherical shape and a homogeneous in size. The well-known crystal structure and optical energy absorption spectrum of Ag-NPs were respectively revealed by the XRD and UV-VIS analysis. This new method is simple and eco-friendly for producing silver and other noble metals in large quantities. The Ag-NPs modified glassy carbon electrode was prepared for nicotine oxidation which indicated that Ag NPs had the ability to enhance the electron transfer rate of the oxidation process. In 0.1 M phosphate buffer (pH of 7.4), a significant increase in the oxidation peak current of nicotine was observed at the modified electrode. Cyclic voltammetry, amperometry, and electrochemical impedance spectroscopy characterizations showed that Ag-NPs had better electrocatalytic performance toward nicotine (NIC) oxidation with good stability, and selectivity. This sensor showed a linear response with the concentration of NIC in the range of 2.5 to 105 μM. The limit of detection (LOD) was estimated to be 0.135 μM. The interference analysis was carried out on the Ag-NPs/GCE with various molecules like acetic acid, ascorbic acid, calcium chloride, glucose, magnesium chloride, urea, and uric acid. Hence, these molecules did not interfere with NIC detection, indicating a perfect selectivity of Ag-NPs/GCE. Moreover, the Ag-NPs/GCE sensor was effectively applied to detect NIC in a real-world sample (saliva) of a tobacco chewer. Furthermore, the Ag-NPs/GCE sensor exhibited very good stability and repeatability in human saliva samples. Finally, Ag-NPs/GCE was also successfully applied to detect spiked nicotine in saliva samples with high recovery value, indicating its high accuracy and effectiveness in NIC analysis.

Cover Feature: Unveiling True Limits of Electrochemical Performance of Organic Cathodes in Multivalent Batteries through Cyclable Symmetric Cells (Batteries & Supercaps 2/2023)

The Cover Feature illustrates a reported cyclable symmetric cell approach that helps illuminate the true electrochemical performance of organic electrodes in multivalent batteries. Cyclable symmetric cells enable both conventional cycling (long-term and high-rate) and advanced electrochemical impedance spectroscopy characterization. By eliminating the metal anode/electrolyte interface in the electrochemical tests, cyclable symmetric cells can improve the comparability of results on multivalent metal/organic batteries published in the literature. More information can be found in the Research Article by J. Moškon, J. Bitenc and co-workers.

Preparation of intelligent corrosion resistant coatings based on pH-responsive silica nanocontainers

This work introduces the synthesis of smart silica nanoparticles loaded with a corrosion inhibitor (2-mercaptobenzothiazole) and embedded in composite organosilane coatings for corrosion protection of carbon steel. Through the BET test, the results show that the mechanically stabilized silica nanoparticles have the characteristics of large specific surface area, narrow pore size distribution and large pore volume. This also provides conditions for sufficient loading of the corrosion inhibitor (CI). Further, smart nano-containers are prepared by encapsulating CI in a layer-by-layer (LBL) self-assembly manner. The anticorrosion properties of the coatings were investigated by electrochemical impedance spectroscopy (EIS) and polarization curve characterization methods. The results indicate that the addition of smart silica nanoparticles can improve the corrosion resistance of the coating. This method simplifies the synthesis process of nanocontainers, which will be widely used in the fabrication of novel nanocontainers and opens up new prospects for active anticorrosion.

Evaluation in Real Conditions of New Anticorrosive Formulations Based on Polyphenols from Natural Sources and Encapsulated Nanoparticles

The objective of this study was to examine the combined protection effect of a two-layer system consisting of organic corrosion inhibitors (tannins derived from the bark of radiata pine) and anodic protection by means of the incorporation of zinc oxide nanoparticles modified superficially by chemical methods to improve the protection of metallic structures against corrosion. Film evaluations are performed in accordance with ISO and ASTM standards. This study also took into account the evaluation of the performance of two commercial coatings according to the scheme suggested by the supplier, in addition to the electrochemical impedance spectroscopy (EIS) characterizations at 0 h, 720 h of accelerated exposure, and 4 months of atmospheric exposure in a corrosive environment of classification C3. The results obtained indicated that the combination of tannins derived from pine bark and encapsulated zinc oxide nanoparticles is a viable alternative to commercial coatings with a higher concentration of synthetic compounds. Although the film properties decrease slightly, performance tests at different exposure times show that they can still be classified as high-performance coatings.

One-step nitrogen defect engineering of polymeric carbon nitride for visible light-driven photocatalytic O2 reduction to H2O2

Polymeric carbon nitride (PCN) is an important metal-free photocatalyst for visible light-driven hydrogen peroxide (H2O2) production from O2 reduction. Herein, we synthesized the DPCN catalysts possessing nitrogen defects by one-step thermal polymerization of urea in N2 stream. As compared to the PCN conventionally synthesized in static air, X-ray photoelectrons spectroscopy (XPS) characterization disclosed that there are more pyridinic N defects in the DPCN catalysts, which is attributed to the removal of a proportion of NH3 released from urea pyrolysis by flowing N2. UV–vis diffuse reflectance spectroscopy (UV–vis DRS), Mott–Schottky, steady-state and time-resolved photoluminescence (PL), and electrochemical impedance spectroscopy (EIS) characterizations revealed that the introduction of the nitrogen defects narrows down the band gap, improves the density of the photoexcited charge carriers, prolongs the lifetime of the charge carriers, and enhances the charge transfer efficiency. In visible light-driven photocatalytic O2 reduction to H2O2, the optimal DPCN catalyst afforded an activity of 4.35 times that of the PCN catalyst and a H2O2 concentration of 2.83 mmol L–1 after 10 h of visible light irradiation. This one-step thermal polymerization approach is valid when replacing N2 stream with Ar and He streams.

Passivity of iron surface in curing cement paste environment investigated by electrochemical impedance spectroscopy and surface characterization techniques

The curing behaviour of cement paste and formation of passive film on iron were investigated by electrochemical techniques and X-ray photoelectron spectroscopy (XPS). Open circuit potential of iron was monitored with the newly developed solid-contact-chloride reference electrode in cement paste with pH ∼13 laid at ∼0 VSHE for 56 d, indicating iron was kept in passive state. Electrochemical impedance spectroscopy results showed significant increasing trend of film and cement paste resistance with curing time. XPS elucidated formation of ferric hydroxide and ferric oxide was efficient to passivate the iron rather than ferrous products. Iron surface receded from corrosion due to high-alkaline environment of cement paste and formation of passive film.