Cathodic Reduction Research Articles

Electrochemical Mechanisms and Optimization System of Nitrate Removal from Groundwater by Polymetallic Nanoelectrodes.

Zn-Cu-TiO2 polymetallic nanoelectrodes were developed using Ti electrodes as the substrate. The reaction performance and pollutant removal mechanism of the electrodes were studied for different technological conditions by analyzing the electrochemical properties of the electrodes in the electrochemical system, using Ti, TiO2, Cu-TiO2, and Zn-Cu-TiO2 electrodes as cathodes and Pt as the anode. The Tafel curve was used for measuring the corrosion rate of the electrode. The Tafel curve resistance of the Zn-Cu-TiO2 polymetallic nanoelectrode was the smallest, so the Zn-Cu-TiO2 nanoelectrode was the least prone to corrosion. The electrode reaction parameters were determined using cyclic voltammetry (CV). Zn-Cu-TiO2 polymetallic nanoelectrodes have the lowest peak position and the highest electrochemical activity. The surface area of the electrode was determined by the time-current (CA) method, and it was found that the Zn-Cu-TiO2 polymetallic nanoelectrode had a larger surface area and the highest removal rate of nitrate. The Ti, TiO2, Cu-TiO2, and Zn-Cu-TiO2 electrodes also had higher removal rates for real groundwater, and the differences between the removal rates of nitrates for deionized water and real groundwater decreased as removal time increased. The Zn-Cu-TiO2 polymetallic nanoelectrode exhibited the highest removal rate for real groundwater. This study reveals the reaction mechanism of the cathode reduction of nitrate, which provides the basis for constructing electrochemical reactors and its application in treating nitrate-contaminated groundwater. A mathematical model of optimized working conditions was created by the response surface method, and optimum time, NaCl concentration, and current density were 93.39 min, 0.22 g/L, and 38.34 mA/cm2, respectively. Under these optimal conditions, the nitration removal rate and ammonium nitrogen generation in the process solution were 100% and 0.00 mg/L, respectively.

Multifunctional Amorphous Co Phosphosulfide-Coated Fe-Co Carbonate Hydroxide for Highly Efficient Overall Water Splitting

Non-noble metal electrocatalysts current represent an appealing alternative to noble metal electrocatalysts for water oxidation reaction in alkaline conditions. However, the poor water reduction reaction activities limit their performance in driving overall water splitting in alkaline electrolytes. Here, we report the preparation of bifunctional amorphous Co phosphosulfide-doped Fe-Co carbonate hydroxide on the surface of Ni foam (Co-S-P/Fe1Co1COH/NF) through hydrothermal and electrochemical techniques. The efficient full water oxidation and reduction properties of the Co-S-P/Fe1Co1COH/NF were verified in pH = 14 medium. The results proved that a phosphorus and sulfur co-depositing catalyst could exhibit excellent anodic oxidation and cathodic reduction activity for full water splitting. Furthermore, the optimal electrocatalyst can afford a current density of 10 mA cm−2 at an overpotential of only 73 mV for hydrogen evolution from water reduction and 50 mA cm−2 at 160 mV for oxygen evolution from water oxidation in 1.0 M KOH solution, showing better activities than most non-noble metal materials. The improved electrocatalytic activities could be attributed to the increased number of active sites and the synergetic cooperation in the prepared material. Additionally, the Co-S-P/Fe1Co1COH/NF catalyst as both cathode and anode only needs a voltage of 1.5 V to achieve 10 mA cm−2 in 1 M KOH solution for full water splitting, which lays a good foundation for full water splitting in practical applications.

Direct Electrochemical Synthesis of 2,3-Disubstituted Quinoline N-oxides by Cathodic Reduction of Nitro Arenes.

The use of electric current in synthetic organic chemistry offers a sustainable tool for the selective reductive synthesis of quinoline N-oxides starting from easily accessible nitro compounds. The reported method employs mild and reagent-free conditions, a simple undivided cell, and constant current electrolysis set-up which provides conversion with a high atom economy. The synthesis of 30 differently substituted quinoline N-oxides was successfully performed in up to 90 % yield. Using CV studies, the mechanism of the selective formation of the quinoline N-oxides was elucidated. The technical relevance of the described reaction could be shown in a 50-fold scale-up reaction.

A Perspective Review on Microbial Fuel Cells in Treatment and Product Recovery from Wastewater

The treatment of wastewater is an expensive and energy-extensive practice that not only ensures the power generation requirements to sustain the current energy demands of an increasing human population but also aids in the subsequent removal of enormous quantities of wastewater that need to be treated within the environment. Thus, renewable energy source-based wastewater treatment is one of the recently developing techniques to overcome power generation and environmental contamination issues. In wastewater treatment, microbial fuel cell (MFC) technology has demonstrated a promising potential to evolve as a sustainable approach, with the simultaneous recovery of energy and nutrients to produce bioelectricity that harnesses the ability of electrogenic microbes to oxidize organic contaminants present in wastewater. Since traditional wastewater treatment has various limitations, sustainable implementations of MFCs might be a feasible option in wastewater treatment, green electricity production, biohydrogen synthesis, carbon sequestration, and environmentally sustainable sewage treatment. In MFCs, the electrochemical treatment mechanism is based on anodic oxidation and cathodic reduction reactions, which have been considerably improved by the last few decades of study. However, electricity production by MFCs remains a substantial problem for practical implementations owing to the difficulty in balancing yield with overall system upscaling. This review discusses the developments in MFC technologies, including improvements to their structural architecture, integration with different novel biocatalysts and biocathode, anode, and cathode materials, various microbial community interactions and substrates to be used, and the removal of contaminants. Furthermore, it focuses on providing critical insights and analyzing various types, processes, applications, challenges, and futuristic aspects of wastewater treatment-related MFCs and thus sustainable resource recovery. With appropriate planning and further studies, we look forward to the industrialization of MFCs in the near future, with the idea that this will lead to greener fuels and a cleaner environment for all of mankind.

Comparison of the Electrochemical Response of Carbon-Fiber-Reinforced Plastic (CFRP), Glassy Carbon, and Highly Ordered Pyrolytic Graphite (HOPG) in Near-Neutral Aqueous Chloride Media

Carbon-fiber-reinforced polymers (CFRP), being conductive, are capable of supporting cathodic oxygen reduction reactions (ORR) and thus promote galvanic corrosion when coupled to many metallic materials. Hence, understanding cathodic processes at carbon surfaces is critical to developing new strategies for the corrosion protection of multi-material assemblies. In the present work, the electrochemical responses of CFRP, glassy carbon, and HOPG (Highly Ordered Pyrolytic Graphite) have been evaluated in a quiescent 50 mM NaCl solution, and their respective activities towards ORR have been ranked. Employing the averages of the specific charges (CFRP, 129.52 mC cm−2; glassy carbon, 89.95 mC cm−2; HOPG, 60.77 mC cm−2) passed during 1 h polarization of each of the 3 carbon surfaces at −1000 mVSCE in the test media as a ranking criterion, the propensities of the 3 carbon surfaces (CFRP, GC, and HOPG) to support cathodic activities that can lead to anodic metal dissolution on galvanic coupling to metallic materials are ranked thusly; CFRP > GC > HOPG. This ranking is consistent with the trend of capacitance values obtained in this work: CFRP (19.5 to 34.5 μF cm−2), glassy carbon (13.6 to 85.5 μF cm−2), and HOPG (1.4 to 1.8 μF cm−2). A comparison of electrochemical data at potentials relevant to galvanic coupling to metals indicated that at these cathodic potential(s) the CFRP surface is the most electrochemically active of the studied carbon surfaces. On the basis of the values and trends of the electrochemical parameters evaluated, it is postulated that the observed differences in the electrochemical responses of these 3 carbon-rich surfaces to ORR are significantly due to differences in the proportions of edge sites present on each carbon surface. These results could provide valuable insights on plausible strategies for designing carbon surfaces and carbon fiber composites with reduced activity toward ORR for corrosion protection applications or enhanced activity towards ORR for energy applications.

Enhanced norfloxacin degradation by three-dimensional (3D) electrochemical activation of peroxymonosulfate using Mn/Cu co-doped activated carbon particle electrode

In this study, Mn/Cu co-doped activated carbon (MCAC) particle electrodes were applied in the three-dimensional (3D) electrical activation of peroxymonosulfate process (E-PMS-MCAC) for norfloxacin (NOF) degradation. Several comparative experiments demonstrated a significant synergy between catalytic and electric activation of PMS in the E-PMS-MCAC process, which could obtain 90.81 % of NOF removal within 60 min. Quenching experiments and EPR analyses revealed thatSO4·-, •OH, 1O2, and reactive Mn(III) were all involved in the E-PMS-MCAC process, while •OH was dominant reactive species for NOF degradation. The different generation ways of reactive species were also explored. Besides, multiple degradation pathways of NOF were proposed, and the toxicity of intermediates was assessed as well. The characterizations of SEM, XRD, and XPS indicated that the cathodic reduction reaction could facilitate electron transfer to Mn(IV), Mn(III), and Cu(c), triggering the sustainable Mn(I)/Mn(III)/Mn(IV) or Cu(I)/Cu(II) redox cycle. It was noted that the addition of Cl- enhanced the NOF removal, while the presence of HCO3-, NO3-, and H2PO4- inhabited it. Finally, the removal efficiencies of other contaminations including p-nitrophenol (PNP), carbamazepine (CBZ), sulfamethoxazole (SMX), and tetracycline hydrochloride (TCH) were also investigated in the E-PMS-MCAC process. All above results suggested that the E-PMS-MCAC process was a high-efficiency and sustainable technology for organic wastewater treatment.

Polychlorinated alkylation annulation of N-arylacrylamide under electrochemical conditions

A novel and unprecedented method for the polychlorinated alkylation annulation of N-arylacrylamide has been developed under electrochemical conditions with diazo salt as the mediator at the cathode reduction and CH2Cl2 as the substrate and solvent.

Electrochemical C(sp3)-H functionalization of ethers via hydrogen-atom transfer by means of cathodic reduction.

The chemo- and stereoselective electrochemical allylation/alkylation of ethers is presented via a C(sp3)-H activation event. The electrosynthetic protocol enables the realization of a large library of functionalized ethers (35 examples) in high yields (up to 84%) via cathodic activation of a new type of redox-active carbonate (RAC), capable of triggering HAT (Hydrogen-Atom-Transfer) events through the generation of electrophilic oxy radicals. The process displayed high functional group tolerance and mild reaction conditions. A mechanistic elucidation via voltammetric analysis completes the study.

Efficient N2 electroreduction to ammonia in an isopropanol–PBS electrolyte using NiFe2O4in situ grown on nickel foam

In situ grown nickel ferrite nanosheets are used as cathode for electro-catalytic N2 reduction. PBS-isopropanol is used as the electrolyte to improve N2 solubility and reduce HER, and higher ammonia production rate and FE are obtained.

Cathodes for Electrochemical Carbon Dioxide Reduction to Multi-Carbon Products: Part II

This is Part II of a focused review of recent highlights in the literature in cathode development for low temperature electrochemical carbon dioxide and carbon monoxide reduction to multi-carbon (C2+) products. Part I () introduced the role of CO2 reduction in decarbonising the chemical industry and described the catalysts and modelling approaches. Part II describes in situ characterisation to improve the understanding and development of catalysts, the catalyst layer and the gas diffusion layer.

Cathodes for Electrochemical Carbon Dioxide Reduction to Multi-Carbon Products: Part I

This is a focused review of recent highlights in the literature in cathode development for low temperature electrochemical carbon dioxide and carbon monoxide reduction to multi-carbon (C2+) products. The major goals for the field are to increase Faradaic efficiency (FE) for specific C2+ products, lower cell voltage for industrially relevant current densities and increase cell lifetime. A key to achieving these goals is the rational design of cathodes through increased understanding of structure-selectivity and structure-activity relationships for catalysts and the influence of catalyst binders and gas diffusion layers (GDLs) on the catalyst microenvironment and subsequent performance.

Recent developments in Pt-based alloy nanoparticles for oxygen reduction reaction in fuel cells

The significance of proton exchange membrane fuel cells (PEMFs) in economic recovery and climate action initiatives following a pandemic is growing. PEM fuel cells depend on precious-metal catalysts (often Pt or Pt-based alloys) to catalyze the reactions occurring at the electrodes. This is especially true for the cathodic oxygen reduction reaction (ORR), which is slow, represents a large source of energy loss, and brings the overall efficiency of fuel cells down. The performance, cost, and durability of these Pt-based catalysts for ORR hinder their widespread commercial application. As a realistic technique for decreasing Pt usage and related costs, researchers have concentrated intensively in recent years on producing more active and stable Pt-based alloy electrocatalysts. This review article mainly focuses on recent literature of Pt-based alloy electrocatalysts for ORR, especially the effect of nanoparticles (NPs) size, and shape and, therefore, the activity and stability of the generated electrocatalysts. The ORR activity and stability of Pt-based alloys such as Pt-Ni, Pt-Cu, and Pt-Fe, as well as other nano electrocatalysts, will be reviewed along with various synthetic approaches.

Coupling electrocatalytic cathodic nitrate reduction with anodic formaldehyde oxidation at ultra-low potential over Cu2O

An HCHO oxidation reaction for electrocatalytic ammonia synthesis was developed to replace the sluggish anodic oxygen evolution reaction involving electrocatalytic oxidative dehydrogenation and tandem reaction pathways.

The effect of tensile strain in Pd-Ni core-shell nanocubes with tuneable shell thickness on urea electrolysis selectivity.

Expanding our understanding of the structure-performance relationship in nanoscale electrocatalysts for urea electrolysis is crucial for efficient urea waste treatment and concomitant cathodic hydrogen production or CO2 reduction. Here, we elucidate the effect of the lattice strain in Pd-Ni core-shell nanocubes on the dominance of urea overoxidation pathway.

Understanding the mechanism and synergistic interaction of cobalt-based electrocatalysts containing nitrogen-doped carbon for 4 e− ORR

Considering that the cathodic oxygen reduction reaction (ORR) is sluggish, it is necessary to develop efficient and durable catalysts to accelerate this reaction.

Cobalt selenide with ordered cation vacancies for efficient oxygen reduction and frigostable Al-air batteries.

Aluminum-air batteries are still inhibited by the sluggish cathodic oxygen reduction reactions, especially in low temperature conditions. Thus, it is urgent to develop efficient electrocatalysts for Al-air batteries to allow their use in extreme weather conditions. In this work, hexagonal Co0.85Se-decorated N,Se co-doped carbon nanofibers (Co0.85Se@N,Se-CNFs) were synthesized via facile carbonization/selenization of electrospun ZIF-67 nanocubes. The as-prepared metallic Co0.85Se with ordered structural cation vacancies endows Co0.85Se@N,Se-CNFs with remarkable oxygen reduction reaction activity, including high onset and half-wave potentials (0.93 V and 0.87 V vs. RHE, respectively). Consequently, the corresponding Al-air battery exhibits superior performance in a wide range of operating temperatures (-40-50 °C). For instance, this Al-air battery exhibits a voltage from 0.15-1.2 V with a peak power density of about 0.7 mW cm-2 at -40 °C. It is expected that TMSe-decorated N,Se co-doped carbon nanofibers could be applied in extensive energy fields.

The synergy between electrochemical substrate oxidation and the oxygen reduction reaction to enable aerobic oxidation.

Aerobic substrate oxidation reactions catalyzed by a heterogeneous catalyst can be looked upon as two independent half-cell reactions, viz. anodic substrate oxidation and the cathodic oxygen reduction reaction (ORR). In this context, Fe PANI/C, a well-known catalyst for the ORR, is chosen to validate this hypothesis, wherein the anodic reaction is hydrazine oxidation. Fe PANI/C shows excellent activity in terms of the electrochemical ORR and hydrazine oxidation in both alkaline aqueous and non-aqueous media and taken together the aerobic oxidation efficacy of hydrazine-like small organic molecules is correlated with the electrochemical outcomes.

A coupled electrocatalytic system with reduced energy input for CO2 reduction and biomass valorization

A cathodic electrochemical CO2 reduction to formate coupled anodic 5-hydroxymethylfurfural electrooxidation to 2,5-furandicarboxylic acid pair electrolysis system was developed for CO2 conversion and biomass valorization with low energy consumption.

Anolyte Enhances Catalyst Utilization and Ion Transport Inside a CO2 Electrolyzer Cathode

Electrochemical CO2 reduction is a promising technology to capture and convert CO2 to valuable chemicals. High Faradaic efficiencies of CO2 reduction products are achieved with zero-gap alkaline CO2 electrolyzers with a supporting electrolyte at the anode (anolyte). Herein, we investigate the effect of anolyte on the electrode properties such as catalyst utilization, ionic accessibility etc. of a CO2 reduction cathode using electrochemical techniques and cell configurations that avoid the complexities related to co-electrolysis. Using 1M KOH as the anolyte and a Cu gas-diffusion-electrode with low Nafion content as the model CO2 reduction electrode, we find that electrode capacitance (proxy for electrochemically active surface area) and ionic conductivity inside the cathode increase approximately 4 and 447 times, respectively, in presence of KOH. Liquid anolyte wets the electrode’s pore structure more efficiently than capillary condensation of feed water vapor. The ionomer coverage is very low, and its distribution inside the electrode is highly fragmented. Surface ion conduction mechanisms inside the electrode are orders of magnitude lower than the bulk ion conduction in presence of anolyte. This study shows that when an anolyte (e.g., KOH) is used, catalyst utilization and ionic accessibility inside the electrode increase significantly.

INFLUENCE OF CATHODE MATERIAL ON COMBINED CATHODE PROCESSES IN AQUEOUS SOLUTIONS OF IRON(II) SULPHATE

Sulfuric acid is present in many enterprises for metal processing and manufacturing of metal parts. Existing methods of regeneration of spent solutions are not effective, in particular, spent sulfate solutions are neutralized with lye or waste from other industries containing solid carbonates and hydroxides. At the same time, sulfate waste is formed, which requires disposal at special landfills. Electrochemical regeneration of spent solutions of sulfate-acid treatment of steel solves the problem of disposal of such spent sulfate solutions with the inclusion of iron sulfates. The kinetics of combined cathodic processes in aqueous solutions of iron (II) sulfate at a concentration of 0.5 mol.·dm–3 of iron (II) sulfate, depending on the cathode material was studied. The research methodology was as follows: model aqueous solutions with a composition (mol∙dm–3): 0.5 iron (II) sulfate with the addition of 0.5 sulfuric acid and a control solution – 1.0 sulfuric acid were prepared from chemicals of high stage of purification by dissolution in distilled water. The study of the kinetics of combined cathodic processes in model aqueous solutions was carried out by the method of linear voltammetry using the MTech PGP-500 S potentiostat. The auxiliary electrode is platinum. The reference electrode is mercury sulfate. Determination of iron (II) ions in the solution was carried out by the permanganatometric method. Based on the analysis of the obtained current-voltage curves, the effectiveness of the application of electrochemical regeneration of model solutions of iron (II) sulfate with sulfuric acid was established, which makes it possible to cathodically deposit iron in the form of foil or metal powder, and through the course of the anodic process - convert sulfates into sulfuric acid. During this process, oxidation of Fe2+ to Fe3+ takes place at the slightly soluble anode. Therefore, it is proposed to use polymer porous diaphragms to prevent Fe2+ from entering the anode space. Platinum and copper were used as cathode material. The choice of cathode material was based on different electrochemical properties of these metals in relation to the hydrogen reaction. The balance research on the regeneration of the model solution was carried out in a three-chamber electrolyzer. The initial test solution was fed into the middle chamber. The cathodic current density was 0.025 and 0.035 A∙cm–2, the working area of the anode and cathode was 85 cm2. A compact iron deposit was obtained on the cathode with 08X12N10T, which peeled off. The analysis of the cathode deposit showed the presence of 0.065% hydrogen in iron. Output according to the current of iron was 92%. The end of the Tafel section of the course of cathodic reduction of iron with electrochemical control occurs due to Fe2+ concentration limitations and the ohmic resistance of adsorbed hydrogen at the boundary of heterogeneous phases. It is proposed to eliminate these limitations due to electrolyte mixing.