Oscillating Structural Transformations in the Electrochemical Synthesis of Graphene Oxide from Graphite.

Electrochemical synthesis of graphene oxide (GO) is known to occur with potential oscillations, but the structural changes underlying these oscillations have remained unclear. In situ time-resolved synchrotron radiation X-ray diffraction demonstrates that the electrochemical synthesis of GO in aqueous H2SO4 can be described as an oscillating reaction. The transformation from graphite to GO proceeds through periodic structural oscillations that correlate with potential cycles. Stage-1 graphite intercalation compound (GIC) is found only at the peak of the potential cycle, but not at the bottom of the cycle. Stage-1 GIC is formed in the first half-cycle from stage-2 GIC and then transforms into "pristine graphite oxide" (PGO) on the lower side of the potential cycle, after which the cycle restarts with the formation of a new portion of stage-1 GIC. Water-washing results in the transformation of PGO into water-swollen GO with d(001) ~11 Å. These periodic structural changes can be considered a new type of oscillating reaction. The presented results provide broad insights into the oscillating structural changes occurring during the anodic graphite oxidation in aqueous H2SO4 and allow for an update of the mechanism of GO electrochemical formation.

Impacts of chloride ions on the electrochemical decomplexation and degradation of Cr(III)-EDTA: Reaction mechanisms of HO• and RCS.

The removal of Cr(III)-organic complexes, encompassing both decomplexation and ligand degradation, presents significant challenges in industrial wastewater treatment. As one of the most common anions in wastewater, Cl- significantly improves the efficiency of electrochemically removing Cr(III)-organic complexes through generated reactive chlorine species (RCS). In the electrochemical chlorine (EC/Cl2) process, extensive experimentation revealed that ClO• plays a dominant role in the degradation of Cr(III)-EDTA, surpassing the effects of free chlorine, direct electrooxidation, HO•, and other RCS. Density functional theory calculations indicated that RCS, primarily Cl• and ClO•, preferentially oxidize the ligand in Cr(III)-EDTA via H-abstraction, whereas HO• trends to attack the Cr atom through electron transfer. The influential factors on the degradation efficiency of Cr(III)-EDTA, Cr(VI) yield, and total organic carbon removal in EC/Cl2 were also assessed, including Cl- concentration, current density, and pH. Real industrial wastewater was employed as a reaction matrix to evaluate the application of the EC/Cl2 process for treating Cr(III)-EDTA, accompanied by energy efficiency calculations. Additionally, a two-chamber reactor was established to simultaneously oxidize Cr(III)-EDTA at the anode and reduce Cr(VI) at the cathode. This study provided insight into developing RCS-dominated AOPs to effectively decomplex and decompose organic Cr(III)-complexes in Cl--containing industrial wastewater.

Electrocatalytic oxidation of hexafluoropropylene oxide homologues in water using a boron-doped diamond electrode.

Hexafluoropropylene oxide (GenX) is a kind of substitute to PFOA, which has been listed in the Stockholm Convention. In this study, GenX was attempted to be degraded using a boron-doped diamond anode in the electrochemical oxidation system. The effects of operating parameters, including current density (0.5-10 mA/cm2), initial pH (3.0-11.49), initial concentration of GenX (20-150 mg/L), electrode distances (0.5-2 cm), electrolyte types (Na2SO4, NaCl, NaNO3 and NaHCO3) and Na2SO4 electrolyte concentration (40-80 mm), on GenX were studied. GenX can almost completely be degraded under the optimal operating parameters after 180 min of electrolysis. Free radical quenching experiments were carried out to investigate the effects of hydroxyl radicals and sulphate radicals on the degradation of GenX. The degradation intermediates were identified based on the ultra-high performance liquid chromatography equipped with a tandem mass spectrometer, and the degradation mechanisms were also proposed. Finally, the toxicities of GenX and its degradation products were evaluated using the QSAR models. The novelty is that the degradation mechanisms of the high concentration GenX (100 mg/L) were elucidated based on the free radical quenching experiments and the intermediates detected, when the degradation ratio reached 100%.

Tuning the Locally Enhanced Electric Field Treatment (LEEFT) between Electrophysical and Electrochemical Mechanisms for Bacteria Inactivation.

Efficient drinking water disinfection methods are critical for public health. Locally enhanced electric field treatment (LEEFT) is an antimicrobial method that uses sharp structures, like metallic nanowires, to enhance the electric field at tips and cause bacteria inactivation. Electroporation is the originally designed mechanism of LEEFT. Although oxidation is typically undesired due to byproduct generation and electrode corrosion, it can enhance the overall disinfection efficiency. In this work, we conduct an operando investigation of LEEFT, in which we change the electrical parameters to tune the mechanisms between electrophysical electroporation and electrochemical oxidation. Pure electroporation (i.e., without detectable oxidation) could be achieved under a duty cycle of ≤0.1% and a pulse width of ≤2 µs. Applying 2 µs pulses at 7-8 kV/cm and 0.1% duty cycle results in 80-100% bacteria inactivation with pure electroporation. A higher chance of oxidation is found with a higher duty cycle and a longer pulse width, where the antimicrobial efficiency could also be enhanced. For water with a higher conductivity, a higher antimicrobial efficiency can be achieved under the same treatment conditions, and electrochemical reactions could be induced more easily. The findings shown in this work improve the fundamental understanding of LEEFT and help optimize the performance of LEEFT in real applications.

Tailoring Defects in B, N-Codoped Carbon Nanowalls for Direct Electrochemical Oxidation of Glyphosate and its Metabolites.

Tailoring the defects in graphene and its related carbon allotropes has great potential to exploit their enhanced electrochemical properties for energy applications, environmental remediation, and sensing. Vertical graphene, also known as carbon nanowalls (CNWs), exhibits a large surface area, enhanced charge transfer capability, and high defect density, making it suitable for a wide range of emerging applications. However, precise control and tuning of the defect size, position, and density remain challenging; moreover, due to their characteristic labyrinthine morphology, conventional characterization techniques and widely accepted quality indicators fail or need to be reformulated. This study primarily focuses on examining the impact of boron heterodoping and argon plasma treatment on CNW structures, uncovering complex interplays between specific defect-induced three-dimensional nanostructures and electrochemical performance. Moreover, the study introduces the use of defect-rich CNWs as a label-free electrode for directly oxidizing glyphosate (GLY), a common herbicide, and its metabolites (sarcosine and aminomethylphosphonic acid) for the first time. Crucially, we discovered that the presence of specific boron bonds (BC and BN), coupled with the absence of Lewis-base functional groups such as pyridinic-N, is essential for the oxidation of these analytes. Notably, the D+D* second-order combinational Raman modes at ≈2570 cm-1 emerged as a reliable indicator of the analytes' affinity. Contrary to expectations, the electrochemically active surface area and the presence of oxygen-containing functional groups played a secondary role. Argon-plasma post-treatment was found to adversely affect both the morphology and surface chemistry of CNWs, leading to an increase in sp3-hybridized carbon, the introduction of oxygen, and alterations in the types of nitrogen functional groups. Simulations support that certain defects are functional for GLY rather than AMPA. Sarcosine oxidation is the least affected by defect type.

Efficient electrochemical oxidation of antibiotic wastewater using a graphene-loaded PbO2 membrane anode: Mechanisms and applications.

This paper aims to develop a flow-through electrochemical system with a series of graphene nanoparticles loaded PbO2 reactive electrochemical membrane electrodes (GNPs-PbO2 REMs) on porous Ti substrates with pore sizes of 100, 150, 300 and 600 µm, and apply them to treat antibiotic wastewater. Among them, the GNPs-PbO2 with Ti substrate of 150 µm (Ti-150/GNPs-PbO2) had superior electrochemical degradation performance over the REMs with other pore sizes due to its smaller crystal size, larger electrochemical active specific area, lower charge-transfer impedance and larger oxygen evolution potential. Under the relatively optimized conditions of initial pH of 5, current density of 15 mA cm-2, and membrane flux of 4.20 m3 (m2·h)-1, the Ti-150/GNPs-PbO2 REM realized 99.34% of benzylpenicillin sodium (PNG) removal with an EE/O of 6.52 kWh m-3. Its excellent performance could be explained as the increased mass transfer. Then three plausible PNG degradation pathways in the flow-through electrochemical system were proposed, and great stability and safety of Ti-150/GNPs-PbO2 REM were demonstrated. Moreover, a single-pass Ti-150/GNPs-PbO2 REM system with five-modules in series was designed, which could consistently treat real antibiotic wastewater in compliance with disposal requirements of China. Thus, this study evidenced that the flow-through electrochemical system with the Ti-150/GNPs-PbO2 REM is an efficient alternative for treating antibiotic wastewater.

New MMO coatings for electro-refinery applications: Promoting the production of carboxylates.

Within the new circular economy paradigm, this work evaluates the performance of tailored mixed metal oxides (MMO) anodes, based on ruthenium and antimony, for their application into an electrochemically-assisted organic refinery process. This process is designed to transform pollutants into value-added products with minimal mineralization. Oxidation of synthetic wastes consisting of phenol solutions was used to validate the electrochemical conversion of phenolic wastes into carboxylates, which are then considered as bricks to be used for electrosynthesis or to produce fuels. The MMO anodes were manufactured using two synthesis routes (Pechini method and ionic liquid method), each followed by one of three different heating treatments: furnace, microwave, and CO2 laser. The selection of the optimal electrode for the organic electrorefinery was based on a combination of physical and electrochemical properties, degradation performance of phenol to carboxylates, and long-term stability, looking for a truly sustainable solution. Results indicate that anodes synthesized by the ionic liquid (IL) method, regardless of the heating treatment, demonstrated superior performance, with larger active areas (with furnace 82 mC cm-2, microwave 97 mC cm-2, and laser 127 mC cm-2) and higher phenol degradation rates, resulting in a greater generation of carboxylates during electrolysis, yielding primarily oxalate and achieving up to 40% conversion with furnace heating. However, laser-treated anodes exhibited greater stability than furnace-made ones, attributed to the formation of an insulating TiO2 layer. Although the electrode with the longest service life did not show the best catalytic properties for minimizing mineralization, the observed variations in coatings with identical chemical compositions highlight the importance of this research. This study positions itself at the forefront of developing more efficient and sustainable electrochemical technologies for organic waste treatment.

Cu/Mn-mediated electron shuttle and high-valent metals enhance hydroxyl radicals production during the electrochemical oxidation on the CuMn-Sb-SnO2 electrode.

In this work, a novel CuMn-Sb-SnO2 anode is developed by a simple, low-cost preparation process. The doping of Cu and Mn causes surface reconstruction, which optimizes its electronic structure, compared to the Sb-SnO2 anode. Experimental results demonstrate that the levofloxacin degradation kinetics constant in the CuMn-Sb-SnO2 system (0.188 min-1) was 8.5 times higher than that in the Sb-SnO2 system, which is surpassing most reported anodes. Moreover, electrochemical characterization also revealed that the CuMn-Sb-SnO2 anode possessed more active sites, higher OEP potential, and lower charge transfer resistance. Notably, electrochemical characterization and EPR experiments confirmed the formation of Cu (III), highlighting their crucial role in promoting the generation of •OH during the catalytic process. Additionally, theoretical calculations and XPS analysis revealed that Cu and Mn rely on self-mediated redox shuttles to act as "electron porters", significantly accelerating internal electron transfer between Sn and Sb to enhance the production of •OH. Furthermore, the CuMn-Sb-SnO2 anode exhibits great practicability due to its efficient degradation of various antibiotics. This study offers valuable new insights into developing novel electrodes for the efficient degradation of antibiotic wastewater.

Critical review on electrooxidation and chemical reduction of azo dyes: Economic approach.

Effective degradation technologies have been extensively investigated and used to remove azo dyes from wastewater for decades. However, no review dealing with both electrooxidation and chemical reduction of azo dyes from an economic and, therefore, application-relevant perspective has been found in the current literature. A novelty of this review article consists not only in the brief summarization and comparison of both methods but mainly in the evaluation of their economic side. Based on the literature survey of the last 15 years, the costs of treatment approaches published in individual research articles have been summarized, and the missing data have been calculated. A broad spectrum of advanced electrode materials and catalysts have been developed and tested for the treatment, specifically aiming to enhance the degradation performance. An outline of the global prices of electrode materials, reducing agents, and basic chemicals is involved. All additional costs are described in depth in this review. The advantages and disadvantages of respective methods are discussed. It was revealed that effective and cheap treatment approaches can be found even in advanced degradation methods. Based on the collected data, electrooxidation methods offer, on average, 30 times cheaper treatment of aqueous solutions. Concerning chemical reduction, only ZVI provided high removal of azo dyes at prices <100 $ per kg of azo dye. The factors affecting total prices should also be considered. Therefore, the basic diagram of the decision-making process is proposed. In the conclusion, challenges, future perspectives, and critical findings are described.

Efficient electrochemical advanced degradation of Red CL and Red WB dyes from the tanning industry using a boron-doped diamond anode.

Electrochemical oxidation (EO), electro-Fenton (EF), and photoelectro-Fenton (PEF) with a BDD anode have been comparatively assessed to remediate solutions of Red CL and/or Red WB azo dyes from real raw water. For the EO process in 50 mM Na2SO4 at pH 3.0, the main oxidant was the heterogeneous •OH generated at the anode, whereas in EF and PEF, the cathodic production of H2O2 and the addition of 0.50 mM Fe2+ catalyst additionally originated homogeneous •OH that enhanced the oxidation of organics. In PEF, the solution was illuminated with a 6 W UVA light. An almost total discoloration was always found operating with a 1:1 mixture of 200 mg L-1 of both dyes in 60 min, whose efficiency increased in the order of EO < EF < PEF. The HPLC analysis of the dye mixture treated by PEF disclosed that its degradation process agreed with its discoloration. A high 74% of COD was reduced due to the oxidative action of hydroxyl radicals and the photolysis of final Fe(III)-carboxylate species with UVA irradiation. The process was accompanied by an energy consumption of 0.76 kWh (g COD)-1, a value similar to the energy consumed by the applied UVA light.

Electrochemical degradation of acetaminophen in urine matrices: Unraveling complexity and implications for realistic treatment strategies.

Urine has an intricate composition with high concentrations of organic compounds like urea, creatinine, and uric acid. Urine poses a formidable challenge for advanced effluent treatment processes following urine diversion strategies. Urine matrix complexity is heightened when dealing with pharmaceutical residues like acetaminophen (ACT) and metabolized pharmaceuticals. This work explores ACT degradation in synthetic, fresh real, and hydrolyzed real urines using electrochemical oxidation with a dimensional stable anode (DSA). Analyzing drug concentration (2.5 - 40 mg L-1) over 180 min at various current densities in fresh synthetic effluent revealed a noteworthy 75% removal at 48 mA cm-2. ACT degradation kinetics and that of the other organic components followed a pseudo-first-order reaction. Uric acid degradation competed with ACT degradation, whereas urea and creatinine possessed higher oxidation resistance. Fresh real urine presented the most challenging scenario for the electrochemical process. Whereas, hydrolyzed real urine achieved higher ACT removal than fresh synthetic urine. Carboxylic acids like acetic, tartaric, maleic, and oxalic were detected as main by-products. Inorganic ionic species nitrate, nitrite, and ammonium ions were released to the medium from N-containing organic compounds. These findings underscore the importance of considering urine composition complexities and provide significant advancements in strategies for efficiently addressing trace pharmaceutical contamination.

Electrochemically producing high-valent iron-oxo species for phenolics-laden high chloride wastewater pretreatment.

Electrochemical advanced oxidation processes (EAOPs) have shown great promise for treating industrial wastewater contaminated with phenolic compounds. However, the presence of chloride in the wastewater leads to the production of undesirable chlorinated organic and inorganic byproducts, limiting the application of EAOPs. To address this challenge, we investigated the potential of incorporating Fe(II) and Fe(III) into the EAOPs with a boron-doped diamond (BDD) anode under near-neutral conditions. Our findings revealed that both Fe(II) and Fe(III) facilitated the generation of high-valent iron-oxo species (Fe(IV) and Fe(V)) in the anodic compartment, thereby reducing the oxidation contribution of reactive chlorine species. Remarkably, the addition of 1000 µM Fe(II) under high chloride conditions resulted in over a 2.8-fold increase in the oxidation rate of 50 µM phenolic contaminants at pH 6.5. Furthermore, 1000 µM Fe(II) contributed to a reduction of more than 66% in the formation of chlorinated byproducts, consequently enhancing the biodegradability of the treated water. Additionally, transitioning from batch mode to continuous flow mode further amplified the positive effects of Fe(II) on the EAOPs. Overall, this study presents a modified electrochemical approach that simultaneously enhanced the degradation of phenolic contaminants and improved the biodegradability of wastewater with high chloride concentrations.

Selective Oxidative Cleavage of Benzyl C-N Bond under Metal-Free Electrochemical Conditions.

With the growing significance of green chemistry in organic synthesis, electrochemical oxidation has seen rapid development. Compounds undergo oxidation-reduction reactions through electron transfer at the electrode surface. This article proposes the use of electrochemical methods to achieve cleavage of the benzyl C-N bond. This method selectively oxidatively cleaves the C-N bond without the need for metal catalysts or external oxidants. Additionally, primary, secondary, and tertiary amines exhibit good adaptability under these conditions, utilizing water as the sole source of oxygen.

A review of electrooxidation systems treatment of poly-fluoroalkyl substances (PFAS): electrooxidation degradation mechanisms and electrode materials.

The prevalence of polyfluoroalkyls and perfluoroalkyls (PFAS) represents a significant challenge, and various treatment techniques have been employed with considerable success to eliminate PFAS from water, with the ultimate goal of ensuring safe disposal of wastewater. This paper first describes the most promising electrochemical oxidation (EO) technology and then analyses its basic principles. In addition, this paper reviews and discusses the current state of research and development in the field of electrode materials and electrochemical reactors. Furthermore, the influence of electrode materials and electrolyte types on the deterioration process is also investigated. The importance of electrode materials in ethylene oxide has been widely recognised, and therefore, the focus of current research is mainly on the development of innovative electrode materials, the design of superior electrode structures, and the improvement of efficient electrode preparation methods. In order to improve the degradation efficiency of PFOS in electrochemical systems, it is essential to study the oxidation mechanism of PFOS in the presence of ethylene oxide. Furthermore, the factors influencing the efficacy of PFAS treatment, including current density, energy consumption, initial concentration, and other parameters, are clearly delineated. In conclusion, this study offers a comprehensive overview of the potential for integrating EO technology with other water treatment technologies. The continuous development of electrode materials and the integration of other water treatment processes present a promising future for the widespread application of ethylene oxide technology.

Sequential high-recovery nanofiltration and electrochemical degradation for the treatment of pharmaceutical wastewater.

The presence of antibiotics in aquatic ecosystems poses a significant concern for public health and aquatic life, owing to their contribution to the proliferation of antibiotic-resistant bacteria. Effective wastewater treatment strategies are needed to ensure that discharges from pharmaceutical manufacturing facilities are adequately controlled. Here we propose the sequential use of nanofiltration (NF) for concentrating a real pharmaceutical effluent derived from azithromycin production, followed by electrochemical oxidation for thorough removal of pharmaceutical compounds. The NF membrane demonstrated its capability to concentrate wastewater at a high recovery value of 95 % and 99.7 ± 0.2 % rejection to azithromycin. The subsequent electrochemical oxidation process completely degraded azithromycin in the concentrate within 30 min and reduced total organic carbon by 95 % in 180 min. Such integrated treatment approach minimized the electrochemically-treated volume through a low-energy membrane approach and enhanced mass transfer towards the electrodes, therefore driving the process toward zero-liquid-discharge objectives. Overall, our integrated approach holds promises for cost-effective and sustainable removal of trace pharmaceutical compounds and other organics in pharmaceutical wastewater.

PANI/GO and Sm co-modified Ti/PbO2 dimensionally stable anode for highly efficient amoxicillin degradation: Performance assessment, impact parameters and degradation mechanism.

The abuse and uncontrolled discharge of antibiotics present a severe threat to environment and human health, necessitating the development of efficient and sustainable treatment technology. In this work, we employ a facile one-step electrodeposition method to prepare polyaniline/graphite oxide (PANI/GO) and samarium (Sm) co-modified Ti/PbO2 (Ti/PbO2-PANI/GO-Sm) electrode for the degradation of amoxicillin (AMX). Compared with traditional Ti/PbO2 electrode, Ti/PbO2-PANI/GO-Sm electrode exhibits more excellent oxygen evolution potential (2.63 V) and longer service life (56 h). In degradation experiment, under optimized conditions (50 mg L-1 AMX, 20 mA cm-2, pH 3, 0.050 M Na2SO4, 25 °C), Ti/PbO2-PANI/GO-Sm electrode achieves remarkable removal efficiencies of 88.76% for AMX and 79.92% for chemical oxygen demand at 90 min. In addition, trapping experiment confirms that ·OH plays a major role in the degradation process. Based on theoretical calculation and liquid chromatography-mass spectrometer results, the heterocyclic portion of AMX molecule is more susceptible to ·OH attacks. Thus, this novel electrode offers a sustainable and efficient solution to address environmental challenges posed by antibiotic-contaminated wastewater.

An insight on the plausible biological and non-biological detoxification of heavy metals in tannery waste: A comprehensive review.

A key challenge for the tannery industries is the volume of tannery waste water (TWW) generated during the processing of leather, releasing various forms of toxic heavy metals resulting in uncontrolled discharge of tannery waste (TW) into the environment leading to pollution. The pollutants in TW includes heavy metals such as chromium (Cr), cadmium (Cd), lead (Pb) etc, when discharged above the permissible limit causes ill effects on humans. Therefore, several researchers have reported the application of biological and non-biological methods for the removal of pollutants in TW. This review provides insights on the global scenario of tannery industries and the harmful effects of heavy metal generated by tannery industry on micro and macroorganisms of the various ecological niches. It also provides information on the process, advantages and disadvantages of non-biological methods such as electrochemical oxidation, advanced oxidation processes, photon assisted catalytic remediation, adsorption and membrane technology. The various biological methods emphasised includes strategies such as constructed wetland, vermitechnology, phytoremediation, bioaugmentation, quorum sensing and biofilm in the remediation of heavy metals from tannery wastewater (TWW) with special emphasize on chromium.

Electrochemistry promotion of Fe(â ¢)/Fe(â ¡) cycle for continuous activation of PAA for sludge disintegration: Performance and mechanism.

In this study, electrochemistry was used to enhance the advanced oxidation of Fe(Ⅱ)/PAA (EC/Fe(Ⅱ)/PAA) to disintegrate waste activated sludge, and its performance and mechanism was compared with those of EC, PAA, EC/PAA and Fe(Ⅱ)/PAA. Results showed that the EC/Fe(Ⅱ)/PAA process effectively improved sludge disintegration and the concentrations of soluble chemical oxygen demand, polysaccharides and nucleic acids increased by 62.85%, 41.15% and 12.21%, respectively, compared to the Fe(Ⅱ)/PAA process. Mechanism analysis showed that the main active species produced in the EC/Fe(Ⅱ)/PAA process were •OH, R-O• and FeIVO2+. During the reaction process, sludge flocs were disrupted and particle size was reduced by the combined effects of active species oxidation, electrochemical oxidation and PAA oxidation. Furthermore, extracellular polymeric substances (EPS) was degraded, the conversion of TB-EPS to LB-EPS and S-EPS was promoted and the total protein and polysaccharide contents of EPS were increased. After sludge cells were disrupted, intracellular substances were released, causing an increase in nucleic acids, humic acids and fulvic acids in the supernatant, and resulting in sludge reduction. EC effectively accelerated the conversion of Fe(Ⅲ) to Fe(Ⅱ), which was conducive to the activation of PAA, while also enhancing the disintegration of EPS and sludge cells. This study provided an effective approach for the release of organic matter, offering significant benefits in sludge resource utilization.

A Tape-Wrapping Strategy towards Electrochemical Fabrication of Water-Dispersible Graphene.

Graphene has achieved mass production via various preparative routes and demonstrated its uniqueness in many application fields for its intrinsically high electron mobility and thermal conductivity. However, graphene faces limitations in assembling macroscopic structures because of its hydrophobic property. Therefore, balancing high crystal quality and good aqueous dispersibility is of great importance in practical applications. Herein, we propose a tape-wrapping strategy to electrochemically fabricate water-dispersible graphene (w-Gr) with both excellent dispersibility (~4.5 mg/mL, stable over 2 months), and well-preserved crystalline structure. A large production rate (4.5 mg/min, six times faster than previous electrochemical methods), high yield (65.4% ≤5 atomic layers) and good processability are demonstrated. A mechanism investigation indicates that the rational design of anode configuration to ensure proper oxidation, deep exfoliation and unobstructed mass transfer is responsible for the high efficiency of this strategy. This simple yet efficient electrochemical method is expected to promote the scalable preparation and applications of graphene.

The Enhanced Performance of NiCuOOH/NiCu(OH)2 Electrode Using Pre-Conversion Treatment for the Electrochemical Oxidation of Ammonia.

Electrochemical oxidation of ammonia is an attractive process for wastewater treatment, hydrogen production, and ammonia fuel cells. However, the sluggish kinetics of the anode reaction has limited its applications, leading to a high demand for novel electrocatalysts. Herein, the electrode with the in situ growth of NiCu(OH)2 was partially transformed into the NiCuOOH phase by a pre-treatment using highly oxidative solutions. As revealed by SEM, XPS, and electrochemical analysis, such a strategy maintained the 3D structure, while inducing more active sites before the in situ generation of oxyhydroxide sites during the electrochemical reaction. The optimized NiCuOOH-1 sample exhibited the current density of 6.06 mA cm-2 at 0.5 V, which is 1.67 times higher than that of NiCu(OH)2 (3.63 mA cm-2). Moreover, the sample with a higher crystalline degree of the NiCuOOH phase exhibited lower performance, demonstrating the importance of a moderate treatment condition. In addition, the NiCuOOH-1 sample presented low selectivity (<20%) towards NO2- and stable activity during the long-term operation. The findings of this study would provide valuable insights into the development of transition metal electrocatalysts for ammonia oxidation.