Cathodic Reduction Research Articles

Electrodeposition of Cu 3D structures suitable for CO2 reduction

Porous Cu foam electrodes, suitable for cathodic CO2 reduction, were deposited in an acidic sulphate solution with different additives to obtain structures with a high real surface area and an adequate mechanical stability. The influence of the electrodeposition time and solution composition on the porosity parameters, microstructure and stiffness of Cu 3D structures was evaluated. Neither ammonium acetate nor polyethylene glycol were found to be effective additives to the Cu sulphate electrolyte to achieve the main objectives. Only the presence of Cl– ions in the deposition solution resulted in a threefold increase in the real surface area and the achievement of a sufficient mechanical stability of the Cu 3D structure. The latter effect is related to the specific influence of Cl– ions during the electrodeposition process on the microstructural characteristics, such as the size of micropores in the walls of holes and crystallite aggregates that form dendritic branches. These structural changes, in contrast to the Cu samples deposited in a solution without additives, resulted in larger real surface areas, while the denser structures deposited in the presence of Cl– ions ensured the mechanical stability of the 3D structure.

Designing a series of RE based carbon composites (RE=Tb, Gd, Ho, Lu, Nd, Sm, Yb, Eu, and Ce)-especially Tb-N-Cs for oxygen reduction enhancement

Iron and nitrogen co-doped carbon materials (Fe–N–Cs) have enormous application prospects in cathodic oxygen reduction reaction (ORR) as efficient electrode materials. However, their stability is of great importance, but is still limited by severe Fenton reaction due to the preferential reaction between Fe2+ and H2O2. This paper intends to rationally design a series of rare earth (RE) metals based carbon matrix anchoring RE centers directly converted from RE oxides and small nitrogen-containing carbon molecules by employing the molten-salts-assisted pyrolysis. A class of prepared RE based carbon (RE-N-Cs) catalysts surprisingly exhibits ORR activities comparable to that of Pt/C. The Tb–N–Cs sample with the best catalytic activity among them was characterized by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) and X-Ray Diffraction (XRD). The characterization results show the presence of Tb single-sites in carbon substrate, with Eonset of 1.06 V and Jd of 6.37 mA cm−2, exceeding those of the commercial Pt/C (Eonset = 0.96 V vs. RHE; Jd = 5.64 mA cm−2).

A review of recent advances in electrochemical and photoelectrochemical late-stage functionalization classified by anodic oxidation, cathodic reduction, and paired electrolysis.

With the resurgence of electrosynthesis in organic chemistry, there is a significant increase in the number of routes available for late-stage functionalization (LSF) of drugs. Electrosynthetic methods, which obviate the need for hazardous chemical oxidants or reductants, offer unprecedented control of reactions through the continuous variation of the applied potential and the possibility of combination with photochemical processes. This capability is a substantial advantage for performing electrochemical or photoelectrochemical LSF. Ultimately, these protocols are poised to become a vital component of the medicinal chemist's toolkit. In this review, we discuss electrochemical protocols that have been demonstrated to be applicable for the LSF of pharmaceutical drugs, their derivatives, and natural substrates. We present and analyze representative examples to illustrate the potential of electrochemistry or photoelectrochemistry for the LSF of valuable molecular scaffolds.

Interface and Defect Engineering in 3D Co3O4‐Ov/TiO2 to Boost Simultaneous Removal of BPA and Cr(VI) upon Photoelectrocatalytic/Peroxymonosulfate (PEC/PMS) System

AbstractThe combination of photoelectrocatalytic (PEC) and peroxymonosulfate (PMS) is an innovative strategy for environmental treatment. And fabricating a highly efficient photoelectrode is the most pivotal factor in PEC reactions. This study designs an advanced Co3O4‐Ov/TiO2 photoelectrode by a dual‐modification strategy encompassing interface engineering and defect engineering. The photoelectric characterization validates the synergy of oxygen vacancies and dual heterojunctions. Simulated electron density distribution and Kelvin probe force microscopy (KPFM) elucidate the charge transfer pathway between Co3O4‐Ov and TiO2. 1O2 and SO4 .− are confirmed to be primarily responsible for the BPA oxidation in PEC/PMS system by radical scavenger experiments and the EPR technique. And the attack sites of BPA are precisely identified based on the Fukui index. Furthermore, density functional theory (DFT) calculations testify that Co3O4‐Ov can improve the adsorption capacity of PMS and reduce the energy barrier of the reaction process, while XPS analysis showed Co3+/Co2+ redox couple can accelerate PMS activation. Enhanced anode oxidation can effectively promote cathode reduction and consequently Co3O4‐Ov/TiO2‐PMS/PEC system presents a superior removal of both pollutants within only 15 min with fast kinetics (0.15 min−1 for BPA, 0.29 min−1 for Cr(VI)). This work provides unique insight into designing a highly efficient PMS/PEC system for simultaneous pollutant treatment.

Electrochemical production of zirconium silicides from KCl–K<sub>2</sub>SiF<sub>6</sub>–ZrO<sub>2</sub> melt

The unique properties of zirconium silicides attract the attention of a large number of authors from various scientific fields. Expansion of application methods also poses the challenge of developing new, more environmentally friendly and affordable methods of production. The most environmentally friendly method without equipment requirements is the electrolysis of the molten salt. The work proposes a method for producing zirconium silicides by electrolysis of the KCl–K2SiF6–ZrO2 melt. In order to substantiate the electrolysis parameters, the kinetics of cathodic reduction was studied and the limiting stage of the process was determined. The structure and phase composition of the cathode deposit were studied using X-ray diffraction and electron scanning microscopy. In the course of the work, conclusions were drawn about the change in the content of the ZrO2 additives on the morphology of the sediment, and it was also suggested that it was possible to obtain zirconium silicides from more accessible raw materials, such as zircon.

In situ synthetic H2 on composite cathode surface for CH4 production from CO2 in microbial electrosyntshesis

Microbial electrosynthesis (MES) is an innovative technology that employs microbes to synthesize chemicals by reducing CO2.This study explores the CH4 production performance at different cathodic reduction potentials in MES. In this study, in situ H2 production on the surface of composite electrode was realized by regulating cathode potential. Pathway for H2-mediated CH4 synthesis was the main synthesis pathway, but it was susceptible to interfere from the external environment (such as cathode potential, pH). The optimal CH4 production potential was −1.0 V vs Ag/AgCl, meanwhile the CH4 synthesis rate was 58 ± 0.4 mLm−2d−1 and the CE was 67 ± 0.5%. Excessively high reduction potentials (−1.4 V vs Ag/AgCl) reduce the activity of microbial populations at the cathode. Synergistic interactions between H2-producing bacteria (Hydrogenophaga, Clostridium, Enterobacter, and Escherichia coli) and Hydrogenotrophic methanogens (Methanobacterium and Methanomassiliicocus) promoted efficient synthesis of CH4. These insights provide new perspectives on reactor operation, thus contributing to the efficiency of MES.

A General Hydrotrifluoromethylation of Unactivated Olefins Enabled by Voltage-Gated Electrosynthesis.

Here we present the first successful hydrotrifluoromethylation of unactivated olefins under electrochemical conditions. Commercially available trifluoromethyl thianthrenium salt (TT+-CF3BF4-, Ep/2 = -0.85 V vs Fc/Fc+) undergoes electrochemical reduction to generate CF3 radicals which add to olefins with exclusive chemoselectivity. The resulting carbon centered radical undergoes a second cathodic reduction, instead of a classical HAT process, to generate a carbanion that can be terminated by protonation from solvent. The use of MgBr2 (+0.20 V onset oxidation potential) plays a key role as an enabling sacrificial reductant for the reaction to operate in an undivided cell. Guided by cyclic voltammetry (CV) studies, fine-tuning the solvent system, trifluoromethylating reagent's counteranion and careful selection of redox processes, this work led to the development of a voltage-gated electrosynthesis by pairing two redox processes with a narrow potential difference (ΔE ≈ 1.00 V) allowing the reaction to proceed with two important advances: (a) high reactivity and selectivity towards hydrotrifluoromethylation over undesired dibromination, and (b) an unprecedented functional group tolerance, including aniline, phenols, unprotected alcohol, epoxide, trialkyl amine, and several redox sensitive heterocycles.

Engineering medium-entropy alloy nanoparticle nanotubes for efficient oxygen reduction

Fuel cells, as promising energy conversion devices, realize the direct conversion of hydrogen fuel chemical energy into electrical energy. The kinetics of cathodic oxygen reduction reaction (ORR) is slow and plays a decisive role in the output efficiency of fuel cells. Platinum catalysts have been commercialized, but their high cost, relatively low catalytic activity and poor cycling durability limit the development of fuel cells. The introduction of non-platinum components is an effective strategy to minimize the cost and maximize the activity. In this study, PtPdCu medium entropy alloy nanoparticle nanotubes (PtPdCu MEANPTs) that demonstrate high catalytic activity and long durability are presented. Combined with density functional theory calculations, the introduction of Pd and Cu modulates surface electronic structure and optimizes the oxygen adsorption energy, thus enhancing the catalytic activity. The 0D/1D hybrid structure exposes more surface sites and inhibits particle maturation. The atomic migration and rearrangement are emerged during the initial stage of potential cycling process, induing a palladium-rich outer layer and preventing the oxidation of platinum atoms. The best-performing Pt24Pd28Cu48 MEANPTs deliver the impressive ORR activity (1.42 A/mgPt at 0.9 V vs. RHE, which is 6.17 times that of commercial Pt/C) and durability (retaining 2.87 times the initial activity of benchmark catalyst after 30,000 potential cycles). Theoretical calculations have confirmed the regulation of alloying on the surface oxygen affinity and revealed the true active sites on the catalyst surface. This work explores the research direction of platinum-based multi-element catalysts with low platinum content and high catalytic activity.

Boosted direct electrochemical reduction of As(III) from arsenic wastewater via Cu(II)-assisted codeposition on a CuIn alloy electrode

Arsenic contamination is a severe environmental problem. A promising strategy for addressing this issue is the direct conversion of highly toxic As(III) to less toxic elemental arsenic (As(0)) using electrochemical reduction technology. In this study, a novel CuIn alloy nanoparticles-modified copper foam (CuIn NPs/CF) was prepared as an efficient cathode for the electrocatalytic reduction of highly mobile As(III) to solid As(0). Density functional theory (DFT) results revealed that the Cu-In bimetallic system exhibited weaker H atom bonding, and the Cu-ln surface was more favorable for the adsorption of *AsO₃ species than the Cu surface. Compared to the pristine CF electrode, CuIn NPs/CF was demonstrated to effectively suppressed the hydrogen evolution reaction with an enlarged hydrogen evolution potential of 1.45 V, and displayed a superior As(0) recovery yield. The conversion of As(III) to As(0) was further enhanced by adding Cu²⁺ to the electrolyte, facilitating a Cu-As co-deposition process. Notably, the CuIn NPs/CF electrode achieved an As(0) recovery yield of 5.38 mg cm⁻² after eight successive recycling tests. This work not only presents a green and sustainable strategy for As(III) removal, but also provides valuable insights into the rational design of Cu-based alloy cathodes for electrocatalytic reduction.

Corrosion of Copper, Cupronickel, Nickel Aluminium Bronze and Super-Duplex Stainless Steel Rotating Cylinder Electrodes in Seawater under Turbulent Flow Conditions

The corrosion of uncoated metals in a marine environment restricts the choice of suitable engineering metals and alloys. Anodic dissolution of metal and cathodic reduction of oxygen are important processes and formation of a surface oxide film can affect both electrode reactions. Charge transfer and mass transfer data can provide information on corrosion rate and mechanism. Several metals and alloys having a history of use in marine engineering are considered, including copper, two copper alloys (cupronickel and nickel aluminium bronze) plus a more recent addition to strong, corrosion resistant alloys (a super duplex stainless steel). The rotating cylinder electrode offers the benefits of a controlled, turbulent flow of electrolyte, facilitating controlled mass transfer in a compact cell geometry which is well-suited to bench-top operation. These features are illustrated using a variety of electrochemical techniques, including open-circuit potential vs time monitoring, linear sweep voltammetry, rotation speed step- or potential step current transients and linear polarisation resistance measurements. Seawater taken from Langstone Harbour, Hampshire, UK, was filtered, air-saturated, pH 8.0 and maintained at 25 °C. Dimensionless group correlations and graphical plots (using an analogous approach to the Koutecky-Levich equation for an RDE) enabled contributions of charge transfer-, mixed- and mass transfer- controlled data to be appreciated, allowing the Tafel slopes of electrode reactions, the diffusion coefficient of dissolved oxygen, the mass transfer coefficient for oxygen reduction and the mean corrosion rate to be estimated.

Catalytic Effect of Titanium Ions on the Cathodic Reduction of Selenium (VI), Copper (II), Uranium (VI) Ions and Other Metals in an Aqueous Solutions

It is known that catalytic processes are widely applied in the field of organic chemistry; however they also play a significant role in inorganic chemistry. Nonetheless, numerous unresolved issues persist in the technology of inorganic substances and the extraction of metals and nonmetals in their elemental states. This publication aims to consolidate the results of our pioneering research utilizing the redox Ti (IV)–Ti (III) system, which demonstrates a catalytic action on the cathodic reduction of selenium (VI), copper (II), platinum (IV), palladium (IV), bismuth, arsenic (V) ions, uranium (VI), as well as manganese dioxide suspension. It has been demonstrated that in the presence of the redox Ti (IV)–Ti (III) system, hard-to-reduce selenate ions can be reduced at room temperature. The catalytic action of the redox Ti (IV)–Ti (III) system has been reliably demonstrated, and the reaction mechanism has been established. In the electrochemical production of metal powders (Cu, Pt, Pd, Bi) at cathode current densities exceeding the limiting value, a portion of the current is irreversibly lost to the discharge of hydrogen ions. Consequently, the current efficiency (CE) for powder production does not exceed 80 %. We have established that in the presence of titanium (IV) ions, due to their catalytic action, the CE increases by more than 15 %. It has also been shown that during the cathodic polarization of hexavalent uranium its reduction to uranium (IV) in the presence of the catalyst increases by more than 50 %. The reduction of hard-to-reduce arsenate ions in the presence of titanium (IV) ions proceeds with high CE to the active trivalent state, and further reduction can proceed electrochemically. The cathodic reduction of a manganese dioxide suspension was investigated. In the presence of a catalyst — titanium (IV) ions, manganese in this dioxide is reduced to the divalent state with a current efficiency exceeding 90 %.

CuS nanoparticle/TiO2 nanosheets heterojuncture boosting paired electrosynthesis of formate

There is still a gap in research on the use of TiO2 as a multiphase catalyst for electrocatalysis. This paper explores the boosting effect of TiO2 nanosheets (NSs) in CuS/TiO2 NSs bifunctional catalysts which enhances their electrocatalytic formate production in both anodic methanol oxidation reaction (MOR) and cathodic carbon dioxide reduction reaction (CO2R). The boosting effect of TiO2 nanosheet is ascribed to the in-built CuS/TiO2 heterojunctions which have abundant heterointerface boundaries, adjusted electrolyte/catalyst environment, improved electrochemical active area as well as facile electron transfer. The cathodic CO2RR with CuS/TiO2 NSs showed a formate Faraday efficiency (FE formate) of 75 % at −0.9 V (vs. RHE), while the anodic MOR exhibited 97 % FE formate at 1.7 V (vs. RHE). Particularly, paired electrolysis of formate was realized in an H-type cell through simultaneous cathodic CO2RR and anodic MOR, achieving a total FE formate of 168.7 % at 10 mA cm−2.

Optimization of Copper Recovery and Fluorine Fixation from Spent Carbon Cathode Reduction Copper Slag by Response Surface Methodology

Optimization of Copper Recovery and Fluorine Fixation from Spent Carbon Cathode Reduction Copper Slag by Response Surface Methodology

Alloying effect-triggered electron polarization in PdCu metallene for simultaneous electrocatalytic upcycling of nitrate and polyethylene terephthalate to value-added chemicals

Electrocatalytic convert nitrate wastewater and discarded polyethylene terephthalate (PET) into high-value chemicals is an effective approach to addressing environmental pollution while generating economic benefits. To achieve this vision, herein, PdCu alloy metallene grown on Ni foam (PdCuene/NF) was synthesized via a one-step solvothermal method and directly used for anodic ethylene glycol oxidation reaction (EGOR), while an additional oxidation-electroreduction treatment was conducted to further convert it into reconstructed PdCuene/NF (r-PdCuene/NF) for cathodic nitrate reduction reaction (NO3RR). With the synergism of metallene array structure and alloying effect, the cathodic r-PdCuene/NF showed an enhanced nitrate-to-ammonia activity with a maximum Faradaic efficiency (FE) of 91.59 ± 2.79 %, while the anodic PdCuene/NF could effectively convert EG into glycolic acid (maximum FE: 92.12 % ± 0.26 %). The coupling of nitrate reduction with PET-derived EG oxidation based on these two materials allowed the simultaneous production of ammonia and glycolic acid with high FEs (>94 %).

Novel dual-photoelectrode Z-scheme PEC system for efficient TBBPA removal and debromination: Performance and promoting mechanism

Herein, a novel dual-photoelectrode Z-scheme photoelectrocatalytic system is created to achieve efficient synergistic anodic oxidation and cathodic reduction for TBBPA degradation and debromination. Based on the polydopamine-modified N-doped TiO2 nanotubes (PN-TNTs) photoanode and polydopamine-modified Cu2O nanowires (PC-CNWs) photocathode, the degradation, debromination and mineralization were 99.4%, 77.7% and 52.1% at 0.7 V under visible light for 2 h. The introduction of PDA enhances the visible light absorption by the TiO2 photoanode and protects the Cu2O photocathode from photocorrosion. The main active species identified by electron paramagnetic resonance (EPR) and scavenger experiments as •OH and e− were found to promote the degradation and debromination of TBBPA by oxidation and reduction, respectively. The degradation pathway of TBBPA was determined by Density Functional Theory (DFT) calculations and HPLC-MS analyses. Comparing the intermediates of single and dual chambers, it demonstrated that the photocathode was able to achieve the continuous debromination of TBBPA and intermediates, which reduced the toxicity. Finally, the stability, reusability and energy consumption were evaluated, confirming the feasibility of the system.

The transient thermomechanical behavior of solid oxide fuel cell during the operation condition variations

Solid oxide fuel cell (SOFC) is a promising energy conversion technology with high efficiency, low emission and fuel flexibility. In practical and dynamic operation, the thermal stress at the interface of different layers can cause cracks or even thermal mechanical failure. This study investigates the transient thermomechanical behavior of SOFC under changing operating conditions. A three-dimensional dynamical model is developed by considering the electrochemical reaction, electron and ion transport, gas diffusion, heat and momentum transfer, and thermal-mechanical interaction. When the operating conditions vary, the time it takes for the thermal stress to reach a steady state is consistent with the time required for heat transfer to stabilize. The electrolyte layer is subjected to the maximum gradient of thermal stress change after the voltage is switched. With an increase in the inlet gas temperature, the change in the cell temperature can be divided into two stages: a rapid rise and a slow rise. Appropriate prolongation of the temperature rise time is beneficial to the thermal stability of SOFC. The increase in inlet gas temperature changes the distribution trend of cell temperature and thermal stress, while the 50 % reduction in cathode and anode inlet velocity changes its magnitude.

Electrochemically Driven Denitrative Cyanation of Nitroarenes.

A practical denitrative cyanation of feedstock nitroarenes under mild and transition metal-free reaction conditions has been developed. The key to success lies in the use of electrochemically driven, inexpensive ionic liquid N-methylimidazolium p-toluenesulfonate-promoted selective cathode reduction of nitroarenes to anilines, followed by diazoation, cathode reduction to form the aryl radical, and the essential radical cyanation process in one pot. Our protocol shows broad functional group tolerance and can be applied for the modification of bioactive targets.

Localized Surface Modification during Alternating Current Scanning Electrochemical Microscopy: Origin and Mechanism

In the current study, we report for the first time the observation of unintended localized surface modification on commercially pure aluminum (Al) during an alternating current scanning electrochemical microscopy (AC-SECM) analysis, its origin, and the probable mechanism responsible for it. Application of an AC perturbation potential (∼100 mV amplitude at ∼100 kHz frequency) to the Platinum ultramicroelectrode (Pt UME), during AC-SECM in acidic, neutral chloride, tap water, and alkaline electrolytes was found to cause surface modification on the scanned region of Al. An increase in the local pH of the electrolyte between the UME and the Al substrate, irrespective of the electrolyte pH (3–11) and UME biasing conditions, led to the local surface modification. The reason for the enhancement of local pH is attributed to the occurrence of higher rates of cathodic reduction reactions than that of anodic oxidation reactions. The reduction of dissolved oxygen/protons/water in the electrolytes led to the generation or consumption of OH−/H+ ions, respectively, and thus increased the pH, whereas the oxidation of Pt UME/Al surfaces decreased the pH with the generation of H+ or consumption of OH− ions. These results contribute significantly to accurately analyzing Al and its alloys using the AC-SECM technique.

N-doped carbon confined ternary Pt2NiCo intermetallics for efficient oxygen reduction reaction

Developing high performance electrocatalysts for the cathodic oxygen reduction reaction (ORR) is essential for the widespread application of fuel cells. Herein, a promising Pt2NiCo atomic ordered ternary intermetallic compound with N-doped carbon layer coating (o-Pt2NiCo@NC) has been synthesized via a facile method and applied in acidic ORR. The confinement effect provided by the carbon layer not only inhibits the agglomeration and sintering of intermetallic nanoparticles during high temperature process but also provides adequate protection for the nanoparticles, mitigating the aggregation, detachment and poisoning of nanoparticles during the electrochemical process. As a result, the o-Pt2NiCo@NC demonstrates a mass activity (MA) and specific activity (SA) of 0.65 A/mgPt and 1.41 mA/cmPt2 in 0.1 mol/L HClO4, respectively. In addition, after 30,000 potential cycles from 0.6 V to 1.0 V, the MA of o-Pt2NiCo@NC shows much lower decrease than the disordered Pt2NiCo alloy and Pt/C. Even cycling at high potential cycles of 1.5 V for 10,000 cycles, the MA still retains ∼70%, demonstrating superior long-term durability. Furthermore, the o-Pt2NiCo@NC also exhibits strong tolerance to CO, SOx, and POx molecules in toxicity tolerance tests. The strategy in this work provides a novel insight for the development of ORR catalysts with high catalytic activity, durability and toxicity tolerance.

Carbon Steel Corrosion Induced by Sulfate-Reducing Bacteria: A Review of Electrochemical Mechanisms and Pathways in Biofilms

Microbial metal corrosion has become an important topic in metal research, which is one of the main causes of equipment damage, energy loss, and economic loss. At present, the research on microbial metal corrosion focuses on the characteristics of corrosion products, the environmental conditions affecting corrosion, and the measures and means of corrosion prevention, etc. In contrast, the main microbial taxa involved in metal corrosion, their specific role in the corrosion process, and the electron transfer pathway research are relatively small. This paper summarizes the mechanism of microbial carbon steel corrosion caused by SRB, including the cathodic depolarization theory, acid metabolite corrosion theory, and the biocatalytic cathodic sulfate reduction mechanism. Based on the reversible nature of electron transfer in biofilms and the fact that electrons must pass through the extracellular polymers layer between the solid electrode and the cell, this paper focuses on three types of electrochemical mechanisms and electron transfer modes of extracellular electron transfer occurring in microbial fuel cells, including direct-contact electron transfer, electron transfer by conductive bacterial hair proteins or nanowires, and electron shuttling mediated by the use of soluble electron mediators. Finally, a more complete pathway of electron transfer in microbial carbon steel corrosion due to SRB is presented: an electron goes from the metal anode, through the extracellular polymer layer, the extracellular membrane, the periplasm, and the intracellular membrane, to reach the cytoplasm for sulfate allosteric reduction. This article also focuses on a variety of complex components in the extracellular polymer layer, such as extracellular DNA, quinoline humic acid, iron sulfide (FeSX), Fe3+, etc., which may act as an extracellular electron donor to provide electrons for the SRB intracellular electron transfer chain; the bioinduced mineralization that occurs in the SRB biofilm can inhibit metal corrosion, and it can be used for the development of green corrosion inhibitors. This provides theoretical guidance for the diagnosis, prediction, and prevention of microbial metal corrosion.