Anodic Degradation Research Articles

Advanced Wastewater Treatment: Synergistic Integration of Reverse Electrodialysis with Electrochemical Degradation Driven by Low-Grade Heat

The reverse electrodialysis heat engine (REDHE) represents a transformative innovation that converts low-grade thermal energy into salinity gradient energy (SGE). This crucial form of energy powers reverse electrodialysis (RED) reactors, significantly changing wastewater treatment paradigms. This comprehensive review explores the forefront of this emerging field, offering a critical synthesis of key discoveries and theoretical foundations. This review begins with a summary of various oxidation degradation methods, including cathodic and anodic degradation processes, that can be integrated with RED technology. The degradation principles and characteristics of different RED wastewater treatment systems are also discussed. Then, this review examines the impact of several key operational parameters, degradation circulation modes, and multi-stage series systems on wastewater degradation performance and energy conversion efficiency in RED reactors. The analysis highlights the economic feasibility of using SGE derived from low-grade heat to power RED technology for wastewater treatment, offering the dual benefits of waste heat recovery and effective wastewater processing.

Anodic degradation of salicylic acid and simultaneous bio-electricity recovery in microbial fuel cell using waste-banana-peels derived biochar-supported MIL-53(Fe)-metal-organic framework as cathode catalyst

This research was aimed to synthesize waste banana peel biochar (BC) supported MIL-53(Fe) metal–organic framework (MOF) (MIL-53(Fe)/BC) as an efficient cathode catalyst for application in a microbial fuel cell (MFC) for the treatment of salicylic acid (SA)-laden wastewater. This investigation marks the first application of such a catalyst in a MFC for SA degradation. The results revealed an increment in power density of MFC-MIL-53(Fe)/BC by 2.34-folds (142.2 ± 1.5 mW/m2) as compared to MFC-MIL-53(Fe) (60.6 ± 1.8 mW/m2). Removal of chemical oxygen demand in MFC-MIL-53(Fe)/BC (93.8 ± 2.2 %) was found to be comparable to MFC-Pt/C (94.6 ± 1.5 %). The MFC-MIL-53(Fe)/BC demonstrated a 91.5 ± 2.0 % biodegradation of SA. The power recovery per unit cost by MFC-MIL-53(Fe)/BC was found to be 380.21 mW/US$, which is significantly higher than MFC-Pt/C (6.08 mW/US$), indicating that MIL-53(Fe)/BC could be an affordable replacement to pricey Pt as cathode catalyst for efficient oxygen reduction reaction.

Efficient ultra-low voltage electrolysis of CO2 coupling with hydrazine oxidation degradation

Transforming carbon dioxide (CO2) into valuable fuels or chemicals through electrolysis represents a promising approach to reduce the carbon footprint. Conventional CO2 electrolysis yet faces a challenge in low energy efficiency due to the energy-intensive oxygen evolution reaction (OER) occurring at the anode. In this study, we present an advanced CO2 electrolysis system that pairs cathodic CO2 reduction with anodic degradation of hydrazine oxidation reaction (HzOR), enabling efficient CO2 electrolysis at an ultra-low voltage. To achieve this objective, two precious-metal-free electrocatalysts have been designed and fabricated. Specifically, a nickel single-atom catalyst anchored on porous carbon nanofibers has been developed for cathodic CO2-to-CO conversion, while a flower-like Ni2Fe2N catalyst grown in-situ on nickel foam has been developed for anodic HzOR. We demonstrate high efficiency of CO production (FECO > 80%) at 100 mA cm−2 with an applied voltage of only 0.45 V by simultaneously degrading hydrazine in a flow cell.

Efficient removal of 2,4,6-trinitrotoluene (TNT) from industrial/military wastewater using anodic oxidation on boron-doped diamond electrodes

With growing public concern about water quality particular focus should be placed on organic micropollutants, which are harmful to the environment and people. Hence, the objective of this research is to enhance the security and resilience of water resources by developing an efficient system for reclaiming industrial/military wastewater and protecting recipients from the toxic and cancerogenic explosive compound—2,4,6-trinitrotoluene (TNT), which has been widely distributed in the environment. This research used an anodic oxidation (AO) process on a boron-doped diamond (BDD) electrode for the TNT removal from artificial and real-life matrices: marine water and treated wastewater. During experiments, TNT concentrations were significantly decreased, reaching the anodic degradation efficiency of above 92% within two hours and > 99.9% after six hours of environmental sample treatment. The presented results show the great potential of AO performed on BDD anodes for full-scale application in the industry and military sectors for TNT removal.

Suppressing Anodic Degradation of Lithium-Ion Batteries by Sinusoidal Waveform Charging Method

The effects of Constant current-Constant voltage charging and combined sinusoidal waveform charging methods on the internal structure of LiFePO4 battery have been discussed in detail in this study. Experimental results clearly indicated that after 600 cycles, the battery that utilized the charging method had retained about 94% of state of health. In the electrochemical impedance analysis and cyclic voltammetry tests, the portion of the SEI film impedance was increased about 0.08 mΩ. In the micro structured view, no significant SEI film formation was observed on the surface of the negative electrode that used the battery in the present charging method. Finally, in the analysis of the SEI film composition, it was found that the Li2CO3 and Li2O content in the Li element was only about 15.97% and 4.42% in the battery employing this charging method, and the battery component contents in the CC-CV charging method were 27.2% and 6.69% respectively.

Impact of Low Catalyst Loading and Incorporation of Additives on Structure and Performance of PEM Electrolyzer Catalyst Layers

Polymer electrolyte membrane water electrolyzers (PEMWEs) are an important technology that can produce renewable hydrogen on demand, although with challenges posed by the slow kinetics of the anodic oxygen evolution reaction (OER) and degradation issues. The degradation of membrane electrode assemblies (MEAs) prepared with Ir-based catalysts is not well understood, especially with lower-loading catalyst layers and intermittent load inputs. This work investigates low-loading IrO2 catalyst layers made with different carbon-based additives, including high-surface-area carbon (HSC), graphitized HSC (gHSC), Vulcan, graphitic carbon nanofibers (gCNFs), graphitic nanoplatelets (gNPs), nitrogen-doped carbon spheres (NCs), Ti carbide (TiC) and Ti carbonitride (TiCN). While carbon-based supports have issues with corrosion at high oxidizing potentials, these materials provide a range of variations in morphology, shape, size, surface area, graphitization, and composition, allowing exploration of the impact of these parameters on catalyst layer structure to identify promising routes to improve catalyst layer structures. Catalyst layers were characterized with electron microscopy and x-ray spectroscopy to assess the distribution of catalyst, carbon additive, and ionomer. This information was correlated with electrochemical performance measurements to elucidate the impact on kinetic site access and mass transport. Selected samples were also subjected to more extended operation to investigate how the initial structures and their performance evolved.

Electrochemical Analysis and Quantification of Anodic Oxidation on Activated Carbon Cloth Electrodes through Cyclic Voltammetry

Capacitive Deionization (CDI) has applications ranging from water purification to biofuels processing. For CDI to be a viable scalable technology, electrode stability is critical. In extended experiments the activated carbon cloth (ACC), used for the electrode, has been previously observed to degrade as a result of surface oxidation reactions. Carbon cloth oxidation can reduce the surface area and alter the pore structure, in turn reducing the adsorption capacity. While the behavior of oxidation is known, a reliable method of quantifying the extent of degradation is lacking. To quantify it, cyclic voltammetry was explored to measure the capacitance of pristine and oxidized carbon cloth samples. A three-electrode electrochemical cell was used to quantify capacitance of activated carbon cloth in 1M NaCl solution. The specific capacitance of carbon cloth that underwent anodic oxidation was lower than cathodic and pristine carbon cloth. Further tests analyzed the change in the severity of the anodic degradation on whether the initial CDI separations were performed on organic or inorganic ions. Scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) was utilized to verify and quantify surface oxidation. Cyclic voltammetry is demonstrated as a simple and reliable method for analyzing and quantifying anodic oxidation on activated carbon cloth electrodes in CDI stacks.

Regulation Mechanism on A Bilayer Li2O‐Rich Interface between Lithium Metal and Garnet‐Type Solid Electrolytes

AbstractThe practical implementation of garnet‐type solid electrolytes, such as Li6.4La3Zr1.4Ta0.6O12 (LLZTO), faces the significant challenge of Li dendrites. Though artificial interfacial strategies are effective in dendrite suppression, further investigation is needed to understand the mechanism of homogeneous Li deposition and its practicability under real‐world conditions. Herein, a bilayer interface is constructed to address these issues. Such a bilayer interface consists of one conformal Li2O‐rich layer, generated by rubbing LLZTO pellets inside molten Li with low‐dose In2O3, and another Li2O layer deposited through atomic layer deposition (ALD). The regulatory effect of the initial Li2O‐rich layer on achieving uniform Li deposition is explored, and the critical current density is enhanced to 2.4 mA cm−2. However, simple interfacial strategy is insufficient to prevent anodic degradation for cycling at room temperature without stack pressure, leading to increased current leakage and directly reducing Li+ within the electrolyte. After insulating it with a second ALD‐Li2O layer that minimally hampers ionic conduction, the Li/Li symmetric cells achieve long cycling life exceeding 1000 h at 0.5 mA cm−2 and maintain stable operation even at 2 mA cm−2. This work provides valuable insights for interfacial strategies towards practical solid‐state batteries.

Synchrotron-Based X-ray Photoelectron Microscopy of LMO/LAGP/Cu Thin-Film Solid-State Lithium Metal Batteries

Solid-state batteries (SSB), characterized by solid-state electrolytes—in particular inorganic ones (ISSE)—are an ideal option for the safe implementation of metallic Li anodes. Even though SSBs with ISSEs have been extensively investigated over the last two decades, they still exhibit a series of technological drawbacks. In fact, mechano-chemical issues, mainly the stability of the electrolyte/anode interface, hinder their widespread application. The present investigation focusses on a thin-film LMO (Lithium-Manganese-Oxide)/LAGP (LiAlGe Phosphate)/Copper, anodeless Lithium-metal battery and explores the morphochemical evolution of the electrode/electrolyte interfaces with synchrotron-based Scanning Photoelectron Microscopy (SPEM) of intact pristine and cycled cells. Chemical images were acquired with submicrometer resolution, to highlight the coupled geometrical and chemical-state changes caused by electrochemical ageing. Geometrical changes of the electrolyte/cathode interface were induced by periodic volume changes, causing de-cohesion of the solid-solid contact, but no chemical-state changes accompany the cathodic damaging mode. Instead, shape changes of the electrolyte/anode region pinpoint the correlation between mechanical damaging with the decomposition of the LAGP ISSE, due to the reduction of Ge, triggered by the contact with elemental Li. The micro-spectroscopic approach adopted in this study enabled the assessment of the highly localized nature of the cathodic and anodic degradation modes in SSB devices and to single out the chemical and mechanical contributions.

Quantitative Analysis of Origin of Lithium Inventory Loss and Interface Evolution over Extended Fast Charge Aging in Li Ion Batteries.

During the extreme fast charging (XFC) of lithium-ion batteries, lithium inventory loss (LLI) and reaction mechanisms at the anode/electrolyte interface are crucial factors in performance and safety. Determining the causes of LLI and quantifying them remain an essential challenge. We present mechanistic research on the evolution and interactions of aging mechanisms at the anode/electrolyte interface. We used NMC532/graphite pouch cells charged at rates of 1, 6, and 9 C up to 1000 cycles for our investigation. The cell components were characterized after cycling using electrochemical measurements, inductively coupled plasma optical emission spectroscopy, 7Li solid-state nuclear magnetic resonance spectroscopy, and high-performance liquid chromatography/mass spectrometry. The results indicate that cells charged at 1 C exhibit no Li plating, and the increase of SEI thickness is the dominant source of the Li loss. In contrast, Li loss in cells charged at 9 C is related to the formation of the metallic plating layers (42%) the SEI layer (38.1%) and irreversible intercalation into the bulk graphite (19%). XPS analysis suggests that the charging rate has little influence on the evolution of SEI composition. The interactions between competing aging mechanisms were evaluated by a correlation analysis. The quantitative method established in this work provides a comprehensive analytical framework for understanding the synergistic coupling of anodic degradation mechanisms, forecasting SEI failure scenarios, and assessing the XFC lithium-ion battery capacity fade.

Kinetic Modeling of the Anodic Degradation of Ni-EDTA Complexes: Insights into the Reaction Mechanism and Products

In this study, an electrochemical advanced oxidation process (EAOP) was employed to effectively degrade complexes of nickel and ethylenediaminetetraacetic acid (EDTA) present in electroless nickel plating wastewaters. Our results show that Ni-EDTA complexes can be effectively degraded by an EAOP with degradation of the complexes occurring at/near the anode surface via interaction with hydroxyl radicals generated on water splitting. Our results further show that the rate of Ni-EDTA degradation is not a function of the rate of any particular chemical reaction but, rather, is controlled by the rate of transport of Ni-EDTA to the anode surface. The oxidation of EDTA to smaller noncomplexing entities releases Ni2+, which is subsequently deposited onto the cathode as Ni0. While complete Ni-EDTA removal and Ni recovery are achieved within 2 h, the overall TOC removal by EAOP is limited, with only 50% TOC removal achieved after 2 h of treatment. The low affinity of small molecular weight EDTA degradation products (such as formic acid, glycine, oxamic acid, and acetic acid) for the anode surface limits oxidation of these compounds and overall TOC removal by the anodic oxidation process. We have developed a mathematical kinetic model that satisfactorily describes Ni-EDTA removal, Ni recovery, and TOC removal over a range of Ni and EDTA concentrations and provides a good description of the oxidation of various EDTA degradation intermediates. The mathematical model developed here, when coupled with the hydrodynamics of the electrochemical cell using a computational fluid dynamics tool, can assist in both cell design and the selection of operating parameters such that the performance of the EAOP process for Ni-EDTA degradation and TOC removal is optimized.

Bidirectional manipulation of iodine redox kinetics in aqueous Fe-I2 electrochemistry.

Catalyzing conversion is a promising approach to unlock the theoretical potentials of the I2/I- redox couple in aqueous Fe-I2 electrochemistry. However, most reported results only obtain one-directional efficient iodine conversion and cannot realize a balance of full reduction and reoxidation, thereby resulting in rapid capacity decay and/or low coulombic efficiency. Herein, the concept of bidirectional catalysis based on a core-shell structured composite cathode design, which accelerates the formation and the decomposition of FeI2 simultaneously during battery dynamic cycling, is proposed to regulate the Fe-I2 electrochemical reactions. Notably, the functional matrix integrates N, P co-doping and FeP nanocrystals into a carbon shell to achieve bidirectional catalysis. More specifically, the carbon shell acts as a physical barrier to effectively capture active species within its confined environment, N, P heteroatoms function better in directing the iodine reduction and FeP facilitates the decomposition of FeI2. As confirmed with in situ and ex situ analysis, the Fe-I2 cell operates a one-step but reversible I2/FeI2 pair with enhanced kinetics. Consequently, the composite cathode exhibits a reversible Fe2+ storage capability of 202 mA h g-1 with a capacity fading rate of 0.016% per cycle over 500 cycles. Further, a stable pouch cell was fabricated and yielded an energy density of 146 W h kgiodine-1. Moreover, postmortem analysis reveals that the capacity decay of the Fe-I2 cell originates from anodic degradation rather than the accumulation of inactive iodine. This study represents a promising direction to manipulate iodine redox in rechargeable metal-iodine batteries.

Experimental Design and Bioassays as Tools to Investigate the Impact of Anodic Oxidation on Progestins Degradation

The present study investigated the degradation of levonorgestrel (LNG) and gestodene (GES) through an anodic oxidation process mediated by active chlorine species. The independent variables [LNG]0 and [GES]0, current density (mA cm−2), and [NaCl]0 (mol L−1) were optimized through a response surface methodology (RSM) based on a four-level central composite design (CCD). Specific energy consumption allowed CCD-RSM analysis and optimization. The decay of progestins was followed to verify the kinetics of the anodic degradation process. Chlorine monitoring showed that excess Cl− concentration did not mean high hormones removal, as well as the excess of current density. Central point conditions ([NaCl]0 = 0.07 mol L−1, j = 32.5 mA cm−2, [LNG]0, and [GES]0 1.0 mg L−1) proved to be the best operational option. The performance with real pharmaceutical wastewater confirmed model optimization (2.2 ± 0.2 kWh g−1, with removals of 83.1 ± 0.9% and 75.1 ± 2.8% for LNG and GES, respectively). The selected condition was used for estrogenic activity and acute toxicity assays. The first allowed the identification of the initial estrogenic activity for the mixture of LNG and GES (924 E2-EQ ng L−1). Additionally, the electrochemical process could decrease this environmental parameter by 74.6%. The progestin mixture was classified as acute toxicity to Daphnia similis, with a toxicity unit (TU) of 2.5 100/EC50%. After electrolysis, the hormone solutions reached a fourfold increase in TU value, classified as high acute toxicity.

Comparative study of dihydroxybenzene isomers degradation and bioelectricity generation using CuO as cathodic catalyst in double chambered microbial fuel cell

A double chambered microbial fuel cell (MFC) showed enormous capacity in the simultaneous degradation of synthetic wastewater and dihydroxybenzene isomers (catechol, resorcinol and hydroquinone) and concurrently with bioelectricity generation. Operating parameter such as effect of catalyst on MFC system was evaluated using bare carbon plate and copper (II) oxide (CuO) loaded carbon plate as cathodes, respectively, in terms of chemical oxygen demand (COD) and dihydroxybenzene isomers removal efficiency, maximum voltage output and power density. Results revealed that the application of CuO loaded carbon plate was more effective in the COD removal of synthetic wastewater in the anodic chamber and degradation of dihydroxybenzene isomers in the cathodic chamber. Compared with the bare carbon plate as cathode, the COD removal efficiency of synthetic wastewater, removal rate of dihydroxybenzene isomers and maximum voltage output increased 20, 100 and 31 %, respectively, when CuO was applied as cathodic catalyst. Among the dihydroxybenzene isomers, hydroquinone exhibited the best performance in both absence and presence of catalyst in the MFC. The position of the substituent of hydroxyl groups possessed significant effect on the reaction rate, reactivity and conductivity of dihydroxybenzene isomers. Hydroquinone was more susceptible to be degraded than that of catechol and resorcinol due to its lower dipole moment which eased the bond cleavage. The intermediate products of degradation of catechol, resorcinol and hydroquinone were determined using gas chromatograph-mass spectrometer and the degradation pathways were proposed.

Electro-Conversion of Lignin to Highly Value-Added Products

After cellulose and hemicellulose, lignin represent the most abundant part of the plant biomass. Due to the large waste stream originating from pulping processes, only Kraft lignin and lignosulfonates are of technical interest. Using electric current as sustainable reagent for degradation avoids transition metal catalysts and makes this approach very attractive. However, the natural complexity and stability of lignin make the depolymerization to useful organic building blocks a highly challenging task. The state of the art in the selective anodic degradation of Kraft lignin and other lignins will be reported. This contribution exclusively deals with the direct electrolysis and ex-cell approaches. The major focus will be given on the generation and cost efficient isolation of vanillin and related building blocks.

Solution acidity and temperature induced anodic dissolution and degradation of through-plane electrical conductivity of Au/TiN coated metal bipolar plates used in PEMFC

A novel composite coating of gold/titanium nitride on stainless steel (Au/TiN/SS) was developed by introducing Au dots onto a TiN coating to improve the corrosion resistance and electrical conductivity of stainless steel bipolar plates for the polymer electrolyte membrane fuel cell (PEMFC). The effects of temperature and pH on conductivity and corrosion resistance of the Au/TiN/SS in a simulated PEMFC environment were investigated. The results showed that the interfacial contact resistance of TiN coating reduced from 5.48 mΩ cm2 to 1.72 mΩ cm2 after introducing the Au dots, indicating that Au dots can enhance the interfacial conductivity of the composite coating on stainless steel. The increases of solution temperature and acidity enhanced the dissolution of TiN as well as the delamination of Au dots from the composite coating, and the corrosion current density (icorr) of Au/TiN coating increased in high temperature and strong acidic environments. The thin layer of TiNxOy and TiO2 around the Au dots was preferentially dissolved to detach the Au from the composite coating, therefore induced the degradation of through-plane electrical conductivity of the Au/TiN coated metal bipolar plates.

Potential Use of Microbial Fuel Cell Technology in Wastewater Treatment

Two options, in regard to applying microbial fuel cells (MFCs) in water treatment, are under discussion, namely the conversion of the chemical energy of organic substrates to electricity, as well as the use their potential to reduce different species, such as the ionic form of copper (Cu2+ converted to metal copper) and iron (Fe3+ converted to Fe2+). The high reduction potential of Cu2+ and Fe3+ makes the processes of electricity production and metal reduction, to be performed simultaneously in MFC, achievable. The electrical yield measurement during the experiments of anodic organic matter degradation by MFC in treating an artificial wastewater with chemical oxygen demand (COD) 0.6 and 1.6 g O2·dm−3, as initial COD, are given. It is demonstrated that the higher organic load is associated with better electrical yield. A comparison of MFC and conventional anaerobic digestion performance is discussed, as well. Experimental proofs of copper removal and phosphate mobilization, following the iron reduction of FePO4, are also reported.

Cover Feature: Development of a Method for Anodic Degradation of Lignin for the Analysis of Paleo‐Vegetation Proxies in Speleothems (ChemElectroChem 6/2022)

The Cover Feature illustrates the pathway of lignin from the plant into a stalagmite and to the electrochemically generated monomeric analytes. More information can be found in the Article by T. Hoffmann et al.

Development of a Method for Anodic Degradation of Lignin for the Analysis of Paleo‐Vegetation Proxies in Speleothems

AbstractHere we present an electrochemical method for the anodic oxidation and subsequent degradation of lignin in speleothems to utilize the resulting lignin oxidation products (LOPs) as paleo‐vegetation markers. LOPs were analyzed using an ultra‐high performance liquid chromatography (UHPLC) system coupled to a high‐resolution mass spectrometer (HRMS). The method presented here achieved comparable or even higher LOP concentrations than established CuO and CuSO4 oxidation methods. The method represents a new tool for the analysis and reconstruction of paleo‐vegetation and has the potential to be applied to other climate archives.

Evaluation of the influence of alumina nano-particle size and weight composition on the corrosion resistance of monolithic AA1070 aluminium

Corrosion resistance of AA1070 aluminium alloy (AA1070) was compared to AA1070 reinforced with alumina at weight composition (wt. %) of 5% and 10%, and grain size of 150 nm and 600 nm. Potentiodynamic polarization and open circuit potential analysis were employed in 0.0125 M H2SO4, 3.5% NaCl and 0.0125 M H2SO4-3.5% NaCl solutions. Data showed 0.0125 M H2SO4-3.5% NaCl solution was the most deleterious with peak corrosion rate value of 6.682 mm/y while 3.5% NaCl solution was the weakest with peak value of 0.084 mm/y. AA1070 at 5% (wt. %) and 150 nm particle size generally displayed the highest corrosion rate with values between 0.084 and 6.682 mm/y. However, visible decrease in corrosion rate occurred with increase in alumina weight fraction and particle size due to growth of the protective oxide on the composite and reduction of discontinuities to minimal values between 0.031 and 2.192 mm/y at 10% alumina weight fraction and 600 nm particle size. Cathodic and anodic reaction mechanisms significantly differs with respect to the electrolyte. Anodic reaction mechanism appeared under activation control in the sulphate-chloride and chloride solution, compared to cathodic reaction mechanism in the sulphate and sulphate-chloride solutions. Significant anodic degradation reaction was prevalent on the anodic polarization plot in the sulphate solution. Plots from open circuit potential analysis shows the composites and monolithic Al were the most thermodynamically stable in H2SO4 solution. In the sulphate-chloride solution, significant potential transients coupled with high corrosion tendency are conspicuous. The plot showed chaotic thermodynamic behaviour active passive transition behaviour of the passive film.