Constant Potential Electrolysis Research Articles

Anodic Dissolution of Al–Fe and Al-Fe-Si Alloys in Emimcl–AlCl3 Electrolyte

To produce over 99.9% of high-purity Al from Al–Fe alloy containing Al6Fe and Al–Fe–Si alloy containing β-AlFeSi by electrorefining, their anodic dissolution and cathodic electrodeposition characteristics were investigated in an EmImCl–AlCl3 ionic liquid electrolyte at 323 K. Constant potential electrolysis showed that Fe dissolved from Al–Fe anode at 0.7 V vs Al/Al(III) and from Al–Fe–Si anode at 1.4 V, and was co-deposited with Al on the cathode. Notably, anodic dissolution potential of Fe was changed by forming β-AlFeSi, and Si did not dissolve from β-AlFeSi at either potential. A combination of controlled anodic dissolution potential and the use of the Al alloy containing β-AlFeSi further suppressed the dissolution and cathodic co-deposition of Fe, affording high-purity Al on the cathode.

Phosphate Ion-Selective Electrode Based on Electrochemically Modified Iron.

The significance of the detection of phosphate ions is immense in the realms of chemistry, biology, medicine, environment, and industry. The detection of phosphate ions is currently mainly reliant on blue molybdenum colorimetry, which is accurate but requires sample pretreatment, intricate operation, and a high price tag. Consequently, it is essential to create a sensor with superior efficiency, precision, straightforward functioning, and instantaneous online detection. This study has designed and created an electrochemical modification based on an iron metal electrode for this purpose. Cyclic voltammetry was used to initially ascertain the potential (-0.57 V) necessary for constant potential electrolysis. Employing a constant potential electrolysis method, the iron oxide and its phosphate were modified onto the surface of the iron electrode to enable reaction with phosphate ions. Scanning electron microscopy and energy dispersive X-ray spectroscopy were used to characterize and analyze the morphology and elemental composition of Fe-PME, elucidating how it responds to phosphate ionation. The two-electrode system was then utilized for the evaluation of the phosphate ion response of Fe-PME at pH 4. Fe-PME's response to phosphate ions is demonstrated by the results, ranging from 10-5 to 0.1 M and with a slope of -52.8 mV dec-1. Fe-PME exhibited satisfactory results when compared to the conventional blue colorimetry of molybdenum.

Post-Functionalization of Thiophene-Fluorene Alternating Copolymers via Anodic Phosphonylation

Phosphonylated polymers are promising materials because of their application in sensor chemistry and their unique electronic properties. Among these polymers, conjugated polymers containing dialkylphosphonate at their side chains have been used in chemical sensors1 and exhibit unique electronic properties.2 However, there have been a few reports on phosphonylation into the conjugated polymer main chains except for poly(3-hexylthiophene) (P3HT)3 and polyaniline derivatives,4 demonstrating that the effect of phosphonate on their main chains has been unclear. To introduce the phosphonate into their main chains, electrochemical post-functionalization is an attractive approach because of the simple protocol and mild reaction conditions.5 Recently, anodic phosphonylation of P3HT at the main chains with trialkyl phosphite was reported.3 However, the applicable precursor polymer is limited to P3HT. Furthermore, the substitution degree was quite low (0.25), indicating that it is necessary to be improved for establishment.Here, to expand applicable precursor polymers and improve the substitution degree, anodic phosphonylation of thiophene–fluorene alternating copolymers (P(Fl-Th)) was conducted (Figure 1), and then we obtained the phosphonylated conjugated polymer (P(Fl-Th-phos(Et)) (substitution degree: 0.26). The obtained polymer showed that phosphonate was introduced selectively into electron-rich thiophene rings. However, the substitution degree was still low. When a 2,6-lutidine was added to the reaction solution, the substitution degree was increased up to 0.83. Furthermore, the substitution degree could be controlled by tuning the amount of charge passed, and the optoelectronic properties of P(Fl-Th-Phos(Et)) were gradually changed through control of the substitution degree. In addition, it was found that various trialkyl phosphite were available in anodic phosphonylation.To functionalize the fluorene units, we carried out anodic phosphonylation of P(Fl-EDOT) which was di-substituted at thiophene moieties, and then the degree of phosphonylation reached 0.75 under the constant-current condition. On the other hand, when we performed constant-potential anodic phosphonylation of P(Fl-EDOT), the substitution degree was improved up to 0.98, indicating that the use of constant-potential electrolysis enabled quantitative anodic phosphonylation.These results demonstrate that anodic phosphonylation can be applied to versatile π-conjugated polymers and that the position of phosphonate introduction can be controlled through the design of appropriate precursor polymers. In addition, due to two alkyl chains, the phosphonate group could enable further modification such as side-chain engineering of conjugated polymers.References G. Zhou, G. Qian, L. Ma, Y. Cheng, Z. Xie, L. Wang, X. Jing, F. Wang, Macromolecules, 2005, 38, 5416–5424.J. Hopkins, K. Fidanovski, L. Travaglini, D. Ta, J. Hook, P. Wagner, K. Wagner, A. Lauto, C. Cazorla, D. Officer, D. Mawad, Chem. Mater., 2022, 34, 140–151.K. Taniguchi, T. Kurioka, N. Shida, I. Tomita, S. Inagi, Polym. J., 2022, 54, 1171–1178.T. Amaya, I. Kurata, Y. Inada, T. Hatai, T. Hirao, RSC Adv., 2017, 7, 39306–39313.T. Kurioka, S. Inagi, Chem. Rec., 2021, 21, 2107–2119. Figure 1

Tuning transition metals layered-electroplated on bimetallic MxCu1−x crystallites (M = Fe, Co, Ni, and Zn) to boost ammonia yield in electrocatalytic reduction of nitrate wastewaters

Nitrate-containing wastewaters have been recognized as an important source for recovering valuable ammonia. This work targets integrating a series of transition metals (M = Fe, Co, Ni, and Zn) onto Cu crystallites through a layered-plating method. The strategy to promote the nitrate reduction reaction (NO3-RR) involves tuning M surfaces in specific ratios for the hydrogenation of nitrogenous species on MxCu1−x electrodes. Electrochemical analysis and operando Raman spectra identified that a solid-state Cu2O-to-Cu0 transition acted as the primary mediator, while its high corrosion resistance protected the M metals or metal oxides from inactivation in nitrate-to-ammonia pathways. Among bimetals, FeCu was the best combination, with the order of performance in constant potential electrolysis, Fe0.36Cu0.64 > Ni0.73Cu0.27 > Co0.34Cu0.66 > Zn0.64Cu0.36. The collaboration of Cu and M in deoxygenating nitrate and subsequently hydrogenating NOx at respective overpotentials is key to enhancing ammonia yield. Nitrate removal (96 %), NH3 selectivity (93 %), and Faradaic efficiency (92 %) were optimized on Fe0.36Cu0.64 electrode at −0.6 V (vs. RHE). A steady yield as high as 14,080 μg h−1 mg−1 was achieved at 30 mA cm−2 using a real water sample (NO3- ∼ 500 mg-N L−1, pH 4) as the input stream, continuously operated for 96 h.

Rational design of porous vanadium-based alloys modified with a Ni-Cu-Mo coating for alkaline water electrolysis

The development of a hydrogen evolution catalyst with both catalytic activity and stability is critical for hydrogen production from electrolytic water. Herein, a V-based porous alloy was prepared via high-energy ball milling and solid-state sintering. Then, the V-based porous alloy was modified with a Ni-Cu-Mo ternary alloy coating by direct current electrodeposition to obtain a composite hydrogen evolution cathode with high hydrogen evolution activity. The substrate has a certain hydrogen storage capacity combined with a high-activity Ni-Cu-Mo coating. The composite hydrogen evolution cathode exhibited high electrocatalytic activity toward the HER. It can afford a lower overpotential of 93 mV and a smaller Tafel slope of 97.4 mV/dec with a current density of 10 mA/cm2 in 1.0 M KOH. The composite hydrogen evolution cathode demonstrated outstanding stability after 2000 cycles and good durability after intermittent electrolysis for 20 h. Hydrogen protons can protect the components of the cathode composite from dissolution during discontinuous constant potential electrolysis. The composite hydrogen evolution cathode also exhibited a strong catalytic capacity for hydrogen evolution during intermittent electrolysis under alkaline conditions.

Cathode Electrochemical Behavior of Aluminum Electrolysis in NaF-NaCl Based Molten Salt

Selective and efficient electrochemical analytical methods for the depositing process of metal aluminum are significant and necessary. The electrochemical measurement methods are based on the means of cyclic voltammetry, square wave voltammetry and constant potential electrolysis. The above methods are used to analyze the depositing process of metal aluminum in NaF-NaCl-Al2O3 and NaF-NaCl-NaAlO2 molten salt. Cyclic voltammetry analysis showed that Al3+ ions were reduced to metal aluminum through two consecutive steps. From the analysis of square wave voltammetry curve, the main reaction on the electrode was the reduction of metal sodium in the NaF-NaCl system, and the electron transfer number of the reaction was 0.80. With the addition of NaAlO2 and Al2O3 in the electrolyte, the electron transfer numbers of the two reduction steps were about 3.0. The process of reduction of Al3+ ions to aluminum was further proved by the analysis of the electrolysis curve at constant potential. The diffusion rate of Al3+ions and the rate of Al3+ reduction reaction increased with the addition of NaAlO2 and Al2O3 and the change of the potential.

Separation of uranium from lanthanides (La, Ce, Nd) and purification of waste salt via aluminum electrodes with different structures in LiCl-KCl eutectic

Aluminum is an ideal cathode material for the pyrochemical reprocessing of spent nuclear fuels. However, there is a lack of large-scale experiments to further assess its performance. Here we designed several Al electrodes with sheet, rod, and porous morphologies, and employed them in separating actinides (An) from lanthanides (Ln) and purifying the waste salts in about 500 g of LiCl-KCl eutectic melt at 773 K. By applying a constant potential of −1.2 V vs. Ag/AgCl, U can be separated from Ln (La, Ce, and Nd) by forming Al-U alloys consisting of Al3U and Al4U with high separation factors and current efficiency. Among all Al electrodes used in our experiments, the porous-shaped ones show the fastest electrochemical reaction rate, and hence only 56 h were required to achieve the separation. Subsequently, the purification of the waste salts from U-Ln separation was conducted via constant potential electrolysis at −1.5 V vs. Ag/AgCl on porous-shaped Al electrodes. About 99.9 % of Ln was extracted via forming Al-Ln alloys, leaving a purified electrolyte that can be reused. In all, about 17 g of U metals and 1 kg of waste salts were successfully reprocessed in our large-scale experiments, which envisions the feasibility of applying Al electrodes in engineering-scale pyrochemical reprocessing.

Electrodeposition behaviour of samarium in 1,3-dimethyl-2-imidazolidone solvent

Abstract The present study investigates the electrochemistry spectroscopy of Sm(III), and electrodeposition of samarium metal in neutral ligand-based ionic liquid (solvate ionic liquid). Mixture consisted of a samarium precursor (either samarium triflate or samarium nitrate hexahydrate) in the solvate ionic liquid, 1.3-dimethyl-2-imidazolidone (DMI). FT-IR analysis of Sm(III)-DMI electrolytes indicates that Sm3+ ion coordinates with DMI through carbonyl group (C=O); the band splits into two with emergence of new peak at 1630 cm−1 and 1649 cm−1 for the triflate and nitrate solutions, respectively. Raman spectroscopy also confirms the solvation of Sm(III) with DMI through oxygen atom of the carbonyl group. Voltametric behaviour of Sm(III) ion indicates two-step reduction mechanism via Sm(III)/Sm(II) at ca. −2.0 V and Sm(II)/Sm(0) at ca. −3.0 V vs. Ag/Ag+ for both samarium(III)-containing electrolytes. Diffusion coefficient value of Sm(III) was determined to be 2.185 × 10−6 cm2/s and 2.418 × 10−8 cm2/s for triflate and nitrate electrolytes, respectively. Electrodeposition of samarium was achieved through constant potential electrolysis using copper substrate as the working electrode which yielded compact deposits from triflate-DMI and non-uniform granular deposit from nitrate-DMI electrolyte. Ex situ X-ray photoelectron spectroscopy analysis of the as-deposited samples revealed the presence of metallic Sm (1081 eV) co-existing with its oxide form (1083 eV).

Mechanistic Insights into Electrocatalytic Hydrogen Evolution by an Exceptionally Stable Cobalt Complex.

Co(aPPy) is one of the most stable and active molecular first-row transition-metal catalysts for proton reduction reported to date. Understanding the origin of its high performance via mechanistic studies could aid in developing even better catalysts. In this work, the catalytic mechanism of Co(aPPy) was electrochemically probed, in both organic solvents and water. We found that different mechanisms can occur depending on the solvent and the acidity of the medium. In organic solvent with a strong acid as the proton source, catalysis initiates directly after a single-electron reduction of CoII to CoI, whereas in the presence of a weaker acid, the cobalt center needs to be reduced twice before catalysis occurs. In the aqueous phase, we found drastically different electrochemical behavior, where the Co(aPPy) complex was found to be a precatalyst to a different electrocatalytic species. We propose that in this active catalyst, the pyridine ring has dissociated and acts as a proton relay at pH ≤ 5, which opens up a fast protonation pathway of the CoI intermediate and results in a high catalytic activity. Furthermore, we determined with constant potential bulk electrolysis that the catalyst is most stable at pH 3. The catalyst thus functions optimally at low pH in an aqueous environment, where the pyridine acts as a proton shuttle and where the high acidity also prevents catalyst deactivation.

RhCuBi Trimetallenes with Composition Segregation Coupled Crystalline‐Amorphous Heterostructure Toward Ethanol Electrooxidation

AbstractThe inefficiency of Pt and Pd benchmark catalysts in achieving complete ethanol oxidation, coupled with their inherent susceptibility to poisoning, poses a significant obstacle to the advancement of direct ethanol fuel cells. In this study, the development of self‐supported and ultrathin RhCuBi trimetallenes, demonstrating exceptional performance in ethanol electrooxidation through segregation and interface engineering is presented. The distinctive RhBi‐rich crystalline/RhCu‐rich amorphous heterostructure of RhCuBi trimetallenes creates a wealth of highly active interfacial sites for the ethanol oxidation reaction (EOR). This results in an impressive 43.3% Faradaic efficiency for the C1 pathway and a peak mass activity of 1.11 A mgRh−1 at 0.68 V versus reversible hydrogen electrode. Moreover, RhCuBi trimetallenes retain 60% of their initial mass activity after 8.5 h of constant potential electrolysis, outperforming commercial Pd and Pt catalysts (<3%). In/ex situ infrared spectroscopy directly reveals the generated C1 products and the key CH3CO* intermediates for EOR on RhCuBi trimetallenes. Theoretical calculations confirm that the RhBi alloy, particularly the lattice‐stretched crystalline/amorphous interfacial sites, facilitates the adsorption/activation of ethanol and the dehydrogenation of CH3CO* toward the C1 pathway of EOR. This breakthrough offers promising prospects for enhancing the efficiency and stability of ethanol electrooxidation in fuel cell applications.

Perchlorate decomposition on rhodium nanoclusters supported on copper crystallite (RhxCu) electrode in an electrodialysis-assisted bipolar electro-reduction system (ED-ER)

Perchlorate (ClO4−) contamination in the aquatic environments presents challenges for remediation due to its high solubility and chemical inertness. A bimetallic RhxCu/Ti was synthesized by incorporating rhodium (Rh) nanoclusters onto the copper crystallites on a titanium mesh substrate for electro-reduction of perchlorate ions. Characterization, which included voltammetry, Raman spectroscopy, and constant potential electrolysis, elucidated the reduction mechanism of perchlorate. A reversible phase transition of Rh(0)⇌ Rh(II) was found to be an effective electron mediator of adsorbed ClO4−, where the neighboring Cu sites were responsible for hydrogenation of chlorinated intermediates. The dispersity of Rh clusters was influenced by the Rh-to-Cu ratio, thereby enhancing the electrochemical reactivity. The bimetallic electrode with around 30 % Rh coverage, i.e., Rh0.3Cu/Ti, possessed superior removal and faradaic efficiency within a potential range of −0.6 V to −0.8 V (vs. Ag/AgCl, at pH 3), which were 95 % and 78 %, respectively. The electro-reduction (ER) and the associated electrodialysis (ED) divided using ion exchange membrane were demonstrated for the treatment of perchlorate wastewater. The electrical field applied by the ED unit drove the migration of ClO4− ions to the surfaces of Rh0.3Cu/Ti cathode, further improving the removal efficiency of perchlorate and lowering energy consumption.

Decrypting the hydrogen evolution in alkaline water with novel magnetoactive cobalt(II) complex-driven cobalt oxide electrocatalysts.

Under the gravity of future socio-economic development, the viability of water electrolysis still hinges on the accessibility of stable earth-abundant electrocatalysts and net energy efficiency. This work emphasizes the design and synthesis of two newly developed cobalt(II) complexes, [Co(HL)2(NCS)2] (Comono) and [Co2(L)3(CH3OH)]ClO4 (Codi), with a (N,O)-donor ligand, HL (2-methoxy-6-(((2-methoxyphenyl)imino)methyl)phenol). The study delves into understanding their structural, morphological, magnetic, and charge transport characteristics. Moreover, the study explores the potential of these complexes in catalyzing hydrogen production through heterogeneous electrocatalysis. The X-ray crystal structure of Comono reveals the octahedral geometry of the Co(II) ion, adopting two HL units and two NCS- units. The Codi complex exhibits a doubly-phenoxo-O-bridged (μ1,1) dinuclear complex, forming a typical octahedral geometry for both the Co(II) centres in coupling with three units of L-. Temperature-dependent magnetic susceptibility measurements showed that all of the Co(II) ion in Comono shows a typical paramagnetic behaviour for high spin octahedral Co(II) ions while the Co(II) centres in Codi are coupled with doubly-phenoxo-bridges bearing weak ferromagnetic characteristics at low temperature. Electron transport properties of the Co(II) complex-mediated Schottky device address the superior carrier mobility (μ) for Codi (9.21 × 10-5) over Comono (2.02 × 10-5 m2 v-1 s-1) with respective transit times of 1.70 × 10-9 and 7.77 × 10-9 s. Additionally, electron impedance spectral analysis supports the lower electrical transport resistance of Codi relative to Comono. The heterogeneous electrocatalytic HER activity of Codi and Comono in 0.1 M KOH shows excellent electrocatalytic efficiency in terms of the various electrochemical parameters. Constant potential electrolysis, multi-cycle CVs, and post-HER analysis reveal the pre-catalytic nature of the complexes, which in turn delivers Co3O4 nanoparticles as the active catalysts for efficient hydrogen evolution.

Electrodeposition Behavior of Al-Au Alloys in AlCl3-NaCl-KCl-Aucl Molten Salt

Quartz Crystal Microbalance (QCM) has been used as a highly sensitive mass sensor. This study aims to form porous gold thin films on QCM elements and apply them to highly sensitive gas sensors by attaching selective media. Physical vapor deposition and chemical etching are known methods for forming porous Au thin films. In this study, the electrochemical formation of porous gold films in AlCl3-NaCl-KCl molten salts containing AuCl was investigated. There are few reports about electrodeposition and dissolution potentials of Au in the molten salt electrolyte. As a first step in this study, voltammogram measurements and constant potential electrolysis were performed in the electrolyte, and electrodeposition potentials of Au and Al-Au alloys were discussed.An electrolyte in this study is a mixture of 61 mol% AlCl3- 26 mol% NaCl- 13 mol% KCl molten salt. The mixture salt was melted at 443 K and AuCl was added to the molten salt. A glassy carbon plate (GC) and a pure Al wire were used as the working electrode and reference electrode, respectively. The GC plate and Au mesh were used as the counter electrode for voltammogram measurement and constant potential electrolysis, respectively. Voltammogram measurements were carried out at potential range from -0.1 to 2.4 V vs. Al/Al(Ⅲ). Constant potential electrolysis was performed in the range from -0.2 to 0.3 V with an electric charge density of 40 C cm-2. The electrodeposits were observed by scanning electron microscopy (SEM) and determined the composition of Al and Au by energy dispersive X-ray spectroscopy (EDS).Au ions concentration in the electrolyte was 2.5 mmol dm-3. In voltammogram measurements, a small cathodic current was observed at about 0.8 V, then gradually increased from 0.2 V. In the potential lower than 0 V, a drastical increase of cathodic current was observed, which was attributed to Al electrodeposition. When the potential was reversed, large anodic current flowed from 0 V and a small current peak was also observed at 0.2 V. These were considered to correspond to the dissolution of Al and Al-Au alloys, respectively. Furthermore, a relatively large anodic current peak was observed at about 2 V, which was expected to be due to the dissolution of Au. From the results of constant potential electrolysis, the Au concentration in the electrodeposits at -0.1 V and -0.2 V was less than 1 at%. At 0 V, the Au concentration in the electrodeposit increased sharply to 84 at%, and at 0.3 V it increased moderately to 89 at%. From SEM observation, the morphology of the electrodeposits at -0.1 V and -0.2 V was dense, while that at potentials more than 0 V was sponge-like.AcknowledgementsThis work was supported by JST SICORP and JPMJSC2108.

Electrochemical Reduction from CO2 to CH4 By Electrodeposited Cu/L-Histidine Hybrid Materials

The electrochemical reduction technology of carbon dioxide (CO2) is attracting attention due to it can convert CO2 into a useful resource with zero emissions by using surplus electricity and renewable energy. For achieving efficient electrolytic reduction of CO2, the development of a high active electrocatalysts is required. Copper (Cu) is the only metal that is capable of electrochemically converting CO2 to hydrocarbons, but the high overpotential of hydrocarbon formation and the low selectivity of the reduction products have been problems. One of the solutions to these problems is the hybridization of metal and organic materials, in which the metal serves as the CO2 reduction reaction sites and the organic material stabilizes the intermediates [1]. In the present study, we have demonstrated electrochemical reduction of CO2 by electrodeposited Cu loading L-Histidine (L-His) which is expecting stabilization of CO2 reductive intermediates hybrids.The electrodeposited Cu/L-His hybrids was obtained by a constant current electrolysis at -1.0~-4.5 mA cm-2 for 1 C cm-2 from the aqueous solutions containing 10 mmol dm-3, CuSO4･5H2O, 0.1 mol dm-3 Na2SO4, and 0.5~20 mmol dm-3 L-His in a three-electrode cell with carbon paper (CP) as the working electrode, platinum wire as the counter electrode, and Ag/AgCl as the reference electrode. The pH of electrolytic bath was controlled between 1.10 and 4.07 by adding H2SO4. The electrochemical reduction of CO2 has been carried out by a constant potential electrolysis at -1.27 V vs. RHE of 0.5 mol dm-3 KHCO3 aqueous solutions saturated with CO2. The amount of reductive gas products was quantified by GC-MS and GC-TCD.The changing the color from pale blue to deep blue was observed by adding L-His into electrolytic bath containing Na2SO4 and CuSO4･5H2O. As increasing concentration of L-His, absorption peak measured by UV-Vis was shifting from around 800 nm originated [Cu(H2O)4]2+ to around 630 nm. The shift was not observed above Cu2+ : L-His = 1 : 2 for molar concentration ratio, therefore, it was considered that Cu2+ and L-His form a complex of [Cu(L-His)2]2+ in aqueous solution. Thus, electrodeposition of Cu/L-His has been tried from Cu2+ : L-His = 1 : 2 aqueous solutions but electrodeposited Cu/L-His cannot achieve. As decreasing pH of electrolytic bath with fixing Cu2+ : L-His = 1 : 2, the absorption peak originated [Cu(L-His)2]2+ was shifting to [Cu(H2O)4]2+ absorption peak. Below pH = 1.7, the absorption peak had been shifted to [Cu(H2O)4]2+ completely and the precipitate was obtained in this condition. The hybridization Cu and L-His was confirmed by Raman spectra. Not only Cu, L-His peaks but also new peak originated L-His adsorbs to Cu were observed. CP has fiber like structure but electrodeposited Cu and Cu/L-His were precipitated such coating CP fiber. The particle size of Cu/L-His hybrids was more homogeneous, and the particles were more densely packed together compared to the pure Cu. However, changing diffraction patterns and peak broadening due to loading organic components in XRD were not observed.The electrochemical reductive reaction of CO2 on ED Cu has been conducted and the faradic efficiency (FE) of CO2 reductive gas product were calculated (Figure). Electrodeposited Cu (ED Cu) showed dramatically improvement of FE from CO2 to CH4 compared to copper foil (Cu foil). Furthermore, the L-His loading electrodeposited Cu (ED Cu/L-His) was more improved than ED Cu. Worthy of a special mention, the amount of hydrogen generation was reduced dramatically by introducing L-His. It can be considered that a reaction field was formed in which the CO2 reduction reaction preferentially takes place over hydrogen evolution. As increasing the concentration of L-His between 0.5~20 mmol dm-3, the FE from CO2 to CH4 goes high until 1.0 mmol dm-3 and then goes down, therefore, it can be observed that high L-His loading inhibits CO2 electrochemical reduction.[1] S. Jia et al., Angew. Chem. Int. Ed. 2021, 60, 10977–10982. Figure 1

Anodic Dissolution Behavior of Al Alloys Containing Al6Fe or β-AlFeSi in EmImCl–AlCl3 Electrolyte During Electrorefining

To produce over 99.9% of high-purity Al from Al alloys containing Al6Fe or β-AlFeSi through electrorefining, their anodic dissolution and cathodic electrodeposition characteristics should be clarified. In this study, the anodic dissolution and cathodic electrodeposition behavior of Al–Fe binary and Al–Fe–Si ternary alloys were investigated in an EmImCl–AlCl3 ionic liquid electrolyte at 323 K. Anodic polarization measurements, constant potential electrolysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), field-emission SEM (FE-SEM), and energy dispersive spectroscopy (EDS) were used to study the anode and electrodeposits on the cathode. Constant potential electrolysis showed that Fe dissolved from Al6Fe in the Al–Fe anode at 0.7 V vs Al/Al(III) and from β-AlFeSi in the Al–Fe–Si anode at 1.4 V and was co-deposited with Al on the cathode. Notably, Si did not dissolve from β-AlFeSi at either potential. A combination of controlled anodic dissolution potential and the use of the Al alloy containing β-AlFeSi further suppressed the dissolution and cathodic co-deposition of Fe, affording high-purity Al on the cathode. This suggests that Al alloys with intermetallic compounds that are less likely to dissolve Fe at the anode are optimal for obtaining over 99.9% of high-purity Al from Al alloys containing Fe in the electrorefining method.

Electrochemical Behavior and Reduction of in LiCl-KCl Molten Salt

In this work, we explored the electrochemical behavior and reduction process of uranyl ions in molten LiCl-KCl eutectic at 773 K. Cyclic voltammetry (CV) and square wave voltammetry (SWV) results showed that the reduction of ions on the inert W electrode was a three-step process: (1) (2) and (3) Electrolysis experiments further confirmed this reduction mechanism that ions were reduced to UO2 on the molybdenum electrode by applying a constant potential of −1.00 V vs Ag/AgCl and subsequently to uranium metal at a more negative potential of −2.35 V vs Ag/AgCl. In addition, ions could be thoroughly reduced to uranium metal through a 4-h constant current electrolysis at −18 mA cm−2. Electronic absorption spectroscopy (EAS) and inductively coupled plasma optical emission spectroscopy (ICP-OES) respectively illustrated that the oxidation state of uranium was unchanged and uranium concentration gradually decreased during the electrolysis. Finally, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the phase composition and microstructure of deposited products. Nano-sized UO2 and U metal particles were successfully obtained by constant potential and current electrolysis. The results of this work further reveal the electrochemical behavior and reduction mechanism of ions in molten LiCl-KCl, providing a guiding ideology for the pyrochemical reprocessing of oxide spent fuels.

Impact of Ag on Electrochemical Recovery of UO2 in Molten LiCl-KCl Salt

To investigate the effect of fission element Ag on the electrochemical recovery of UO2, the electroreduction mechanisms of Ag+ and kinetic property of Ag+/Ag couple were first studied on W electrode by different electrochemical techniques. The electrode reactions of Ag+ and were found to be one-step and two-step reduction processes, respectively. The exchange current density of Ag+/Ag couple was estimated to be 0.0431∼0.0727 A cm−2 in the temperature range of 723∼798 K by LP technique, and its activation energy was evaluated to be 33.91 kJ mol−1. The deposition products obtained by constant potential electrolysis (CPE) were characterized by XRD and SEM-EDS, which showed the formed Ag and UO2 having pine-branch and micron-scale polyhedral structure, respectively. The influence of Ag+ on the electrochemical behavior of and morphology of UO2 were studied. The deposition potential of Ag+ was close to that of to UO2. The changes of Ag+ concentration and scan rate had no effect on the electroreduction mechanism of CPE was conducted, and the result indicated that UO2 and Ag could be co-deposited. The deposited Ag could change the morphology of recovered UO2.

Separation of lanthanides erbium and ytterbium on indium electrodes by modulated potential selective extraction in molten salts and a thermodynamic and kinetic analysis of the process

The main purpose of this paper is to study the extraction and separation of key fragment elements based on the electrolytic refining process of spent fuel dry reprocessing. Firstly, the electrochemical mechanisms of Er(III) and Yb(III) in LiCl-KCl molten salts were investigated on W and In film electrodes with applied cyclic voltammetry (CV), square wave voltammetry (SWV) and open circuit potential (OCP) at 773 K. The results indicated that the reduction behaviour of In(III) and Yb(III) ions were a two-step transfer process and Er(III) ions was a one-step transfer process. Then, the kinetic parameters in electrochemical processes were calculated on an In electrode with different temperatures. The OCP approach was used to determine the equilibrium potential of Er(III)/Er(0) in the temperature range of 773 K∼848 K, and thermodynamic parameters of the In3Er alloy were provided. Based on electrochemical behaviour results, the electrochemical extraction of Er(III) and Yb(III) from LiCl-KCl-ErCl3 molten salts and LiCl-KCl-YbCl3 molten salts at liquid In electrodes was performed by constant potential and constant current electrolysis, respectively. The electrolysis products were determined by X-ray diffraction (XRD), scanning electron microscopy and energy dispersive spectrometry (SEM-EDS), the primary intermetallic compounds generated in the alloys were In3Er and In3Yb. The average extraction rates for Er(III) and Yb(III) were 94.70% and 96.54%, respectively, according to inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis. Er(III) and Yb(III) were selectively extracted and separated from LiCl-KCl-ErCl3-YbCl3 molten salts by potentiostatic control on the basis of the previously studied Lns (Er and Yb) extraction on In electrodes. The separation rate of Er(III) and Yb(III) by electrochemical selective deposition was 94.21%.

Electrochemical separation of fission element neodymium using plumbum electrode from molten LiCl–KCl based on spent fuel reprocessing

In order to investigate the application prospects for the extraction of fission products neodymium (Nd) by electrolytic refining at active plumbum (Pb) electrodes, the reduction mechanism of Nd(III)/Pb(II) at inert tungsten, and Nd(III) at Pb thin film electrodes was investigated. This work simultaneously presents the results of kinetic and thermodynamic parameter of Pb(II)/Nd(III). The composition of the Pb–Nd alloy compound formed on the activated Pb electrode was determined by X-ray diffraction analysis (XRD) and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS), and the thermodynamic parameters of the formed Pb3Nd alloy were calculated: ΔHf0Pb3Nd=−219.92kJmol−1 and ΔSf0Pb3Nd=−47.48Jmol−1K−1. Nd(III) was extracted in the form of Pb–Nd alloy by constant potential electrolysis (PE) in LiCl–KCl melt. Based on the analysis of inductively coupled plasma-atomic emission spectrometry (ICP-AES) results, the average extraction rate of Nd(III) ions at the liquid Pb electrode could reach 99.03%.

Simultaneous electrochemical detection of oxygen (O2) and hydrogen peroxide (H2O2) in neutral media

The simultaneous detection of oxygen (O2) and hydrogen peroxide (H2O2) in neutral media was investigated by cyclic voltammetry using a two-working modified glassy carbon (GC) electrode system. Both electrodes were functionalized either by electrodeposited or by chemically-prepared gold nanoparticles (AuNPs). AuNPs electrodeposition was achieved by constant potential electrolysis either at 0.5 or ‐0.5 V/SHE in acidic HAuCl4 solution. Colloidal AuNPs were obtained according four different procedures (type A to D) derived from the classical Turkevich synthesis and further drop-casted on GC. The kinetics of H2O2 oxidation was studied by recording steady-state voltammograms in a deaerated NaCl/NaHCO3 pH 7.4 neutral solution on all the functionalized electrodes and favorably compared to unmodified GC and bare gold electrodes. Both Koutecky-Levich and Tafel treatment of the current-potential curves showed that the highest anodic transfer coefficient αn (0.78 ± 0.14) was obtained with the electrodeposited AuNPs/GC electrode using the most cathodic deposition potential of ‐0.5 V which provided the highest average number of nanoparticles per square micrometer (555 ± 49 µm-2) of very little average size (25 ± 12 nm) NPs. The simultaneous detection and quantification of O2 and H2O2 was achieved only with electrodes functionalized using D-type Turkevich synthesis. In this case H2O2 was detected at the anode while current corresponding to O2 reduction was selectively recorded at a potential close to ‐0.3 V without interference from H2O2.