Constant Current Electrolysis Research Articles

Electrochemical Performances of a Solid Oxide Electrolysis Short Stack Under Multiple Steady-State and Cycling Operating Conditions

Solid oxide electrolysis cells (SOECs) are increasingly utilized in hydrogen production from renewable energy sources, yet high degradation rates and unclear degradation mechanisms remain significant barriers to their large-scale application. Consequently, endurance testing of stacks under various operating conditions and studying the degradation mechanisms associated with these conditions is imperative. However, due to the generally poor performance consistency among stacks, multi-condition data from numerous stacks lack reliability. In this experimental study, having established a specific SOEC stack’s performance and optimal conditions, durability tests under varied conditions, including various current densities, current operation modes (cyclic or constant current), fuel utilization rates, and temperature cycles were conducted. Electrochemical analysis tools like electrochemical impedance spectroscopy and distribution of relaxation time were employed to analyze the causes of voltage fluctuations under high current densities. The results confirmed that the SOEC stack could handle current cycling at low current densities and constant-current electrolysis at high current densities and withstand at least two temperature cycles.

Rational design of pulse-electrolysis protocols promotes molten-salt electrorefining

Molten-salt electrorefining (MSE) is currently the primary method for purifying many elements, offering promise for the sustainable upcycling of spent metals in the future. However, the conventional constant-current electrolysis protocol inevitably leads to deterioration of the microenvironment near the electrode, leading to reaction runaway and process inefficiency. In this work, we comprehensively studied for the first time the effect of constant- and pulse-electrolysis protocols on environmental evolution in electrode–electrolyte interfaces during the MSE of Ti, using a computer model. The results showed that compared to constant electrolysis, pulse-electrolysis protocols could effectively regulate the interfacial microenvironment and improve the electrorefining efficiency. Furthermore, a correlation between interfacial reconstruction and pulse parameters was established, indicating that the duty ratio was the key factor in inhibiting the deterioration of the interfacial microenvironment. To further verify the simulation results, the real-time morphological evolution of the electrodes during electrolysis was monitored by a novel in situ X-ray computed tomography (CT) technology under pulse-electrolysis protocols. The experimental results indicated that the pulse-electrolysis protocols enhanced the interfacial microenvironment and promoted electrolysis efficiency. Collectively, this work demonstrated that MSE could be effectively advanced by rationally designing the pulse-electrolysis protocols, facilitating its large-scale application in industry.

Anodic Desulfurization of Heterocyclic Thiones - A Synthesis to Imidazoles and Analogues.

An electrochemical desulfurization of 2-mercapto-imidazoles to the corresponding imidazole is established. This novel anodic transformation is bromide-mediated and easy to conduct in the simplest electrochemical setup, consisting of an undivided cell, carbon electrodes, and constant current electrolysis. The method proved successful in 14 diverse examples of imidazoles and triazoles with up to a 97% yield. The scalability was proven in the multigram synthesis of a technically relevant N-heterocyclic carbene (NHC) ligand precursor.

A Voltage-Controlled Strategy for Modular Shono-Type Amination.

Shono-type oxidation to generate functionalized heterocycles is a powerful method for late-stage diversification of relevant pharmacophores; however, development beyond oxygen-based nucleophiles remains underdeveloped. The limited scope can often be ascribed to constant current electrolysis resulting in potential drifts that oxidize a desired nucleophilic partner. Herein, we report a voltage-controlled strategy to selectively oxidize a broad scope of substrates, enabling modular C-N bond formation from protected amine nucleophiles. We implement an electroanalytically guided workflow using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) to identify oxidation potentials across a range of heterocyclic substrates. Controlled potential electrolysis (CPE) selectively generates α-functionalized C-N products in moderate to good yields using carbamate-, sulfonamide-, and benzamide-derived nucleophiles. The importance of voltage control is further exemplified through a systematic study comparing our developed CPE method to constant current electrolysis (CCE) protocols. Voltage-guided CCE and traditionally optimized CCE reveal the importance of maintaining voltage control for high yields and selectivity over a broad scope; a case study with a morpholine-derived substrate illustrates the negative impact of potential drifting under CCE. Sulfonamide drugs, which have significant oxidation potential overlap with model substrates, are rendered competent nucleophiles under CPE. Lastly, sequential voltage-controlled C-N and C-O functionalization of a model substrate generates difunctionalized pyrrolidines further broadening the utility of this reaction.

Detachment Suppression of NiCo Oxide Catalyst Layer for Oxygen Evolution Anode in Alkaline Medium Using Start and Stop Simulated Accelerated Degradation Test Protocol

INTRODUCTION While the alkaline water electrolysis (AWE) has the advantage of low cost and mass production, it has the issue of catalyst coated electrode degradation caused mainly by catalyst layer detachment due to reverse currents generated by the start and stop of variable renewable electricity. A previous study reported that heat treatment of a NiCo2O4 spinel catalyst-supported electrode (NiCo) on a Ni substrate suppress delamination of the catalyst layer with decrease in initial activity due to increase of electrode resistance. [1] In this study, in order to find optimize preparation for both initial activity and durability of the anode electrode catalyst, we compared and evaluated the degradation behavior of NiCo electrodes prepared various conditions. EXPERIMENTAL The accelerated durability test (ADT) was performed in a three-electrode cell with 7 M KOH aqueous solution as electrolyte at 25℃. RHE, Ni coil and 1 cm2 electrode of NiCo spinel catalyst supported on Ni mesh substrate prepared with 8 to 24 of layered thermal decomposition coating at various temperature are used as reference, counter and working electrodes, respectively. Here, the thickness of the coting was determined by Co loading measured with XRF. Constant current electrolysis at 1 A cm-2 for 2 hours was conducted as pretreatment at 80℃ before ADT. The ADT protocol consisted of three steps [2] (Fig.1): (1) constant current electrolysis at 600 mA cm-2 for 1 min, (2) potential scanning from open-circuit potential (OCP) to anodic potential E min (= 0.5 V vs. RHE) at sweep rate of -500 mV s-1, and (3) holding at constant potential of E min for 1 min. To evaluate the anode activity, CV (potential range: 0.5 to 2.0 V vs. RHE, sweep rate: 5 and 50 mV s-1, 3 cycles) and AC impedance measurements (bias potential: 1.6, 1.7 V vs. RHE, frequency range: 106-10-1 Hz, amplitude: 10 mV) were performed at every 200 ADT cycles in 2,000 cycles of ADT. RESULTS AND DISCUSSION As shown in Fig. 2 of the anode potential as a function of the ADT cycle, the potential of the 350°C prepared anode significantly increased around 800 cycles toward around 1.9 V vs. RHE, while the 450°C prepared anode showed slowly and constantly increase in potential.As shown in Fig. 3 of the redox peaks in cyclic voltammograms, the NiCo redox peaks around 1.2 V vs. RHE disappeared and the Ni redox peaks around 1.2 V vs. RHE appeared at the end of the ADT,. The NiCo redox peak of the 350°C prepared anode was significantly larger than the Ni redox peak in the initial period, whereas the Ni redox peaks became larger than the NiCo redox peak around 700 cycles. The charge of NiCo redox peak of the 450°C prepared anode gradually decreased and that of the Ni oxidation peak increased and they reversed for 8, 16, and 24 layered anodes at 1000, 1400, and 1600 cycles, respectively, but NiCo redox peak still remained. These results means that the consumption of the NiCo oxide electrocatalyst occurs during the ADT and the 450°C preparation suppress rapidly detachment of the 450°C prepared anode around 700 cycles.As shown in Fig. 4 of the polarization curves, the OER activity of the 8 layered at the 450°C prepared was almost same as that of the 350°C prepared anode at 200 cycles, and the 16 and 24 layered at 450°C prepared were higher activity than the 350°C prepared and the 8 layered at 450°C prepared. The Tafel slopes of the initial ADT (200 cycles) were almost the same for the 350°C and 450°C. The slope for the 450°C prepared anodes after 2000 cycles were almost same as the initial regardless of the number of applications, but the slope for the 350°C prepared increased. This result also suggests NiCo oxide of the 450°C prepared still remained at the end of the ADT and it dominates oxygen evolution reaction, while the 350°C prepared electrocatalyst completely consumed during the ADT. ACKNOWLEDGEMENTS This study was based on results obtained from the Development of Technologies for Realizing a Hydrogen Society (P20003) commissioned by the New Energy and Industrial Technology Development Organization (NEDO). REFERENCES [1] N. Todoroki, K. Nagasawa, H. Enjoji, S. Mitsushima., ACS Appl. Mater. Interfaces, 15, 20, 24399 24407 (2023).[2] A. Abdel Haleem, K. Nagasawa, Y. Kuroda, Y. Nishiki, A. Zaenal, S. Mitsushima., Electrochem., 89, 2, 186 191 (2021). Figure 1

Electrochemical NH-Sulfoximidation with α-Keto Acids.

An electrochemical N-acylation of sulfoximine has been achieved via the coupling of α-keto acids and NH-sulfoximines. This process involves the sequential cleavage of C-C bond followed by C(sp2)-N bond formation, with the liberation of H2 and CO2 as the by-products. A library of N-aroylated sulfoximines is produced via the coupling of aroyl and sulfoximidoyl radicals by anodic oxidation under constant current electrolysis (CCE). The compatibility of the present protocol has been demonstrated by coupling of various bio-active compounds, such as NH-sulfoximine derived from (-)-borneol, L-menthol, D-glucose derivative, and some commercial drugs such as flurbiprofen, and ibuprofen. This late-stage functionalization highlights the importance of this sustainable protocol. Besides this, various control experiments and detection of H2 evolution have been performed to support the proposed mechanism.

The Active Chlorine Mediated Electrochemical Synthesis of Aromatic Nitriles through Cascade Reaction

An efficient and transition-metal-free synthesis strategy of aromatic nitriles from corresponding aldehydes with H2SO4(NH2OH)2 as the nitrogen source and Cl−/ClO− as the redox mediator was developed. The redox Cl−/ClO− showed electrochemical reversibility in acidic condition. The possible mechanism involving the transformation of Cl−, the generation and electrochemical reduction of nitrile oxides based on the results of cyclic voltammetry and constant current electrolysis was proposed.

Stability and energy consumption of solid oxide electrolysis cells under wide fluctuating and stable conditions

The combination of solid oxide electrolysis cells (SOECs) with renewable electricity has enormous potential, but this requires the cells to be able to adapt to strong fluctuation conditions. This work directly combines fluctuating actual wind power with flat-tube Ni-YSZ/YSZ/LSCF-GDC SOECs to study the operational stability and energy consumption under wide fluctuation and constant current electrolysis. The results indicate that under an average electrolysis current density of 0.26 A cm−2, there is little difference in stability between fluctuation and constant current electrolysis. At a high current density of 0.58 A cm−2, the cells operating for 375 h under fluctuation conditions exhibit a larger degradation rate. The current density is dynamically switched between 0 and 0.93 A cm−2 to simulate actual wind turbine power fluctuations from 0 to 100 %. After rapid large-scale current switches for 2000 times in 375 h, little change is observed in the cell structure. Under fluctuating electrolysis, the minimum energy consumption for power-to-gas conversion in SOEC is 2.84 kWh/Nm3, while under constant current electrolysis, the lowest energy consumption is 2.67 kWh/Nm3. In summary, SOECs can efficiently and stably consume and store highly fluctuating renewable power and can also dynamically respond to wide power ranges from 0 to 100 %.

Electrochemical deposition combined with high-temperature molecular sieve adsorption strategy: Efficient removal of key fission element yttrium for purification of radioactive molten salts

In order to realize energy cost savings in waste salt recycling and electrolysis processes during the nuclear fuel cycle, this paper presents a novel approach for the purification of waste molten salt by employing molecular sieves to absorb excess fission products selectively. The method is founded on the principles of electrolytic refining to achieve sustainable development of reprocessing. In this study, a systematic investigation of the electrochemical reduction/oxidation processes of Y(III)/In(III) was performed on electrode, as well as the electrode reaction of Y(III) on an In electrode at 773 K. Constant-current electrolysis produced an extraction rate of 93.11 % for Y(III) on the In electrode. In order to improve the current efficiency, greatly save the processing cost, and realize the sustainable development of dry post-processing. Subsequently, the waste molten salt environment following electrolysis was simulated, and the fission product was effectively adsorbed utilizing 5A molecular sieves, resulting in a yttrium removal rate of up to 99.94 %. This process not only significantly reduces the cost of electrolysis but also enhances the removal efficiency of target nuclides. The study examined the molten salt adsorption mechanism of molecular sieve, determining the primary adsorption mechanism to be chemical one (ion exchange), through the application of pseudo-first-order, pseudo-second-order, and Weber-Morris kinetic models for re-evaluation.

Facile Synthesis of U2Ti Intermetallic by Direct Electrochemical Reduction of UO2-TiO2 Composite in LiCl-Li2O Melt

Alloys of U with Ti are of importance in nuclear industry as fuel for Gen IV fast reactors, hydrogen isotope storage medium for fusion reactors, super conductors, and also as corrosion resistant material for use in various applications. Here, preparation of U2Ti intermetallic compound was investigated by the direct electrochemical reduction of mixed oxide of UO2-TiO2 in LiCl-0.5% Li2O molten salt at 650 °C. The mixed oxide pellet of UO2-TiO2 sintered at 1500 °C was found to be a mixture of UTi2O6 and UO2 as evidenced by X-ray diffraction (XRD) analysis. Direct electro-lithiothermic reduction of UO2, TiO2, and a mixture of sintered UO2-TiO2 and UTi2O6 coupled with cyclic voltammetry of these oxides in the melt was performed to understand the electro-reduction mechanism. Potentials of reduction of these oxides in the melt, w.r.t Ni/NiO reference electrode, obtained by analysis of CV data of these oxides contained in metallic cavity electrodes and XRD analysis of partially electro-reduced oxides were used to arrive at the electro-reduction mechanism. Results indicate that U2Ti can be prepared conveniently by the electro-lithiothermic reduction of sintered pellet of UO2-TiO2 cathode by constant current electrolysis in a two-electrode cell.

Two-Phase Electrosynthesis of Dihydroxycoumestans: Discovery of a New Scaffold for Topoisomerase I Poison.

Coumestan represents a biologically relevant structural motif distributed in a number of natural products, and the rapid construction of related derivatives as well as the characterization of targets would accelerate lead compound discovery in medicinal chemistry. In this work, a general and scalable approach to 8,9-dihydroxycoumestans via two-electrode constant current electrolysis was developed. The application of a two-phase (aqueous/organic) system plays a crucial role for success, protecting the sensitive o-benzoquinone intermediates from over-oxidation. Based on the structurally diverse products, a primary SAR study on coumestan scaffold was completed, and compound 3 r exhibited potent antiproliferative activities and a robust topoisomerase I (Top1) inhibitory activity. Further mechanism studies demonstrates that compound 3 r was a novel Top1 poison, which might open an avenue for the development of Top1-targeted antitumor agent.

Theoretical Understanding of Effects of Operating Modes on the Performance Durability of Solid Oxide Cells: A Comparison between Potentiostatic and Galvanostatic Operations

In solid oxide cells (SOCs), the choice between galvanostatic (constant current) and potentiostatic (constant voltage) modes does not significantly affect the performance of SOCs as long as the cell components remain unchanged and intact. However, the degradation of cell components, which leads to changes in electrochemical and physical properties of the cell, elevates the importance of the selected operating mode. This paper aims to investigate the effects of galvanostatic and potentiostatic operating modes on the evolving properties of SOCs and their subsequent influence on performance durability. Employing non-equilibrium thermodynamic analysis, a crucial approach for understanding the degradation phenomena within an active electrochemical system, this study aims to provide in-depth insights into how these operating modes affect the longevity and efficacy of SOCs. Key findings include: In cases where oxygen electrode (OE) degradation is accelerated by higher partial pressure of oxygen ( pO2 ), operating under constant voltage electrolysis can mitigate the high pO2 at the OE|electrolyte (OE|EL) interface. Conversely, if OE degradation occurs more rapidly under a lower pO2, constant current electrolysis is more effective in suppressing degradation by achieving a high pO2 at the OE|EL interface. For degradation of the fuel electrode (FE) due to higher pO2, constant current electrolysis is beneficial for more stable performance, which helps maintain low pO2 at the FE|EL interface. When FE degradation is accelerated by lower pO2, constant voltage electrolysis can avert low pO2 at the FE|EL interface. In practical scenarios, more complex degradation mechanisms come into play, especially when pO2 significantly deviates from initial conditions. Degradation in one electrode can influence pO2 in the other electrode, a phenomenon more pronounced in potentiostatic than in galvanostatic electrolysis.

Anodic Oxidation of Aliphatic and Aromatic Amides, Bisamides and Related Derivatives

AbstractThe current comprehensive review covers four main parts, of which some are presented in the form of a personal account. 1. Anodic oxidation of a) N‐alkyl and N,N‐diallyl carbonyl moieties, b) Azacycloalkyl amides and the effect of ring‐size on the outcome, c) Lactams, d) Sulfonamides, and e) The effect of a substituent R attached to carbonyl (N−CO−R) or sulfonamides (N−SO2R) on their oxidation potentials. 2. Anodic oxidation of aromatic amides, in particular of type Ph2CHCONHAr, lacking hydrogen(s) at the α‐position to nitrogen. They undergo three types of bond‐cleavage, yielding a variety of fragmentation products. 3. a) Anodic oxidation of symmetrical bisamides of type ZCONH(CH2)nNHCOZ (Z=Me, Ph, Ar; n=2–4) under constant current electrolysis, in methanol. For n=3, 4 they afford mostly mono‐ and dimethoxylation products. For n=2 they undergo ′CH2−CH2′ bond cleavage to yield fragmentation products. b) Anodic oxidation of symmetrical bisamides of type ArCONH(CH2)2NHCOAr under controlled potential electrolysis, in acetonitrile, leads to gem‐unsymmetrical bisamides of type ArCONHCH2NHCOMe as the major product, in fair yields. 4. Utilization of the anodic process in organic synthesis to form C−C bonds by both intra‐ and inetrmolecular processes; as well as C−O and C−N bonds for generating heterocycles.

Electrochemical CO2 conversion in eutectic Li-Ba and Li-Ca carbonate mixtures

Here, the impact of electrolyte selection and electrolysis temperature on carbon morphology, energy consumption, and voltage efficiency in molten Li2CO3-BaCO3 and Li2CO3-CaCO3 electrolytes during 90 min 10 A constant current electrolysis are investigated. The scarcity of experimental investigations into these binary electrolytes, coupled with a lack of systematic investigation of temperature effects, necessitates further examination. The comprehensive analysis of the produced carbon reveals that both electrolyte composition and temperature influence carbon morphology. At lower temperatures the effect of electrolyte composition to the morphology is a more significant. The type and amount of metallic impurities mixed with the carbon vary depending on the electrolyte composition and electrolysis temperatures. The results from Li2CO3-CaCO3 electrolyte show more promising compared to results from Li2CO3-BaCO3 electrolyte in terms of product quality. Regarding electrolysis power and voltage efficiency, Li2CO3-CaCO3 proves equal or superior to other electrolytes, depending on temperature. Heat generation occurs in all the experiments, which emphasizes the importance maintaining a constant electrolysis temperature in industrial processes to manage heat generation effectively.

Study on the air atmosphere molten salt electrolytic extraction of tungsten and cobalt from cemented carbide scrap

In this study, tungsten and cobalt were extracted from cemented carbide scrap by three-stage electrodeposition in Na2WO4 molten salt at 900 °C in air atmosphere. The cemented carbide scrap was used as the consumable anode, while the cemented carbide calcined material was used as the electrolytically active substance additive. The composition of the cemented carbide calcined material was determined by thermodynamic calculations combined with XRD phase analysis. The study investigated the promoting effect of air atmosphere on anode oxidation and the effect of varying the molar ratio of tungsten to cobalt in the molten salt on product composition. Cyclic voltammetry was used to analysed the cathodic reduction behaviour of tungsten and cobalt. The nucleation mechanism of tungsten and cobalt was determined to be instantaneous by chronoamperometry. Finally, metallic tungsten and cobalt were successfully separated and extracted by three-stage constant current electrolysis.

Controlled Pore Size of NiO-YSZ Tubular Substrate for Improved Performance of Reversible Solid Oxide Cell Using LaGaO3 Electrolyte Film

Effects of channel size in NiO-YSZ porous substrate were studied on power density in solid oxide fuel cell mode and electrolysis current in steam electrolysis mode. It was found that the cell deposited on anode substrate with larger pore diameter shows a superior performance. The LSGM cell prepared on Ni-YSZ tube with average channel diameter of ca. 2.5 μm shows the maximum power density of 0.36 W cm−2 in SOFC mode and 0.42 A cm−2 at 1.6 V in SOEC mode at 873 K. Spike potential noise which may be caused by insufficient gas diffusion in NiO-YSZ porous substrate was observed under constant current electrolysis condition in case of NiO-YSZ tube with narrow channel and the spike noise is suppressed by increasing channel size. NiO-YSZ tube with large channel size is also effective for increasing long term stability in electrolysis mode.

Performance evolution analysis of solid oxide electrolysis cells operating at high current densities

Hydrogen generation by water electrolysis using solid oxide electrolysis cells (SOECs) is highly promising because of the favorable thermodynamics and kinetics. Commercial applications require SOEC operating at high current densities (ǀiǀ≥1 A·cm−2) to achieve substantial hydrogen production rates. This study demonstrates the operation of a full-size Ni–yttria-stabilized zirconia (Ni–YSZ) cell with an effective area of 16 cm2 at −2 A·cm−2 for 336 h, illustrating the feasibility of operating SOECs at a high current density. The electrochemical characteristics of the SOEC evolved during constant current electrolysis, exhibiting an activation stage with a degradation rate (DR) of 54.6 mV/100 h, followed by a rapid decline process(DR: 180.9 mV/100 h), a gentle decline period (DR: 105.5 mV/100 h), and a stable stage (DR: 11.0 mV/100 h). The contributions of individual processes to cell degradation during each process are identified using the distribution of relaxation times (DRT) and subsequent equivalent circuit model (ECM) fitting. The results suggest that the Ohmic resistance, ionic transport and charge-transfer reaction in the Ni-YSZ fuel electrode contribute the most to performance loss. Ni redistribution is regarded as the dominant degradation mechanism, as verified by detailed post-test characterization.

Electrochemical selenofunctionalization of unactivated alkenes: access to β-hydroxy-selenides.

This work demonstrates the electrochemical construction of 2-methyl-1-aryloxy-3-(arylselanyl)propan-2-ol/2-hydroxy-2-methyl-3-(arylselanyl)propyl 2-(2-hydroxy-2-methyl-3-(arylselanyl)propoxy)benzoate starting from aryl allyl ethers/allyl benzoates and diaryl diselenides under additive-free electrochemical conditions. This environmentally friendly method was achieved through constant current electrolysis in an undivided cell setup under acid, oxidant, or catalyst-free conditions. Additionally, this technique enabled the synthesis of a variety of β-hydroxy selenides including late-stage functionalization of drug derivatives in good to exceptional yields across various substrates under mild reaction conditions.

Electrochemically driven regioselective construction of 4-sulfenyl-isochromenones from o-alkynylbenzoates and diaryl disulfides.

Herein, we report a convenient and environmentally friendly electrochemical technique that enables the regioselective construction of 4-sulfenyl-1H-isochromen-1-ones using readily available precursors such as o-alkynyl benzoates and diaryl disulfides. This electrochemical process has been accomplished through constant current electrolysis in an undivided cell under external acid, catalyst, oxidant, or metal-free conditions. Owing to this protocol's mild reaction conditions, the products are obtained in good to very good yields, demonstrating a broad substrate scope and functional group tolerance.

Electro-oxidative coupling of Bunte salts with aryldiazonium tetrafluoroborates: a benign access to unsymmetrical sulfoxides.

An electrochemical strategy for the synthesis of unsymmetrical sulfoxides has been explored using Bunte salts and aryldiazonium tetrafluoroborates under constant current electrolysis at room temperature. In addition to being eco-safe and using mild conditions, the present protocol is free from the use of metal/oxidant, and is endowed with a broad substrate scope and good functional group tolerance.