Rest Potential Research Articles

Synthesis and characterization of titanium oxynitride catalyst via direct ammonia nitridation of titanium polyacrylate for oxygen reduction reaction

AbstractA titanium oxynitride catalyst for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells was synthesized through the direct ammonia nitridation of titanium complexes. Titanium polyacrylate was employed as the catalyst precursor, and the effect of the calcination temperature between 600 and 1000 °C on the catalyst structure was studied. The catalysts were characterized via X-ray diffraction, X-ray absorption spectroscopy, transmission electron microscopy, cyclic voltammetry, and powder electrical resistivity measurements. The formation of titanium oxynitride particles and deposited carbon was observed for all the samples; however, significant variations in the catalyst structure and catalytic activity were also observed. With an increase in the calcination temperature, nitridation of titanium oxynitride progressed, and the conductivity of the catalyst powder increased. The highest rest potential and ORR current density were achieved with calcination at 800 °C. Importantly, the results suggest that maintaining an optimal nitrogen doping level within the catalyst particles, along with ensuring the formation of electroconductive deposited carbon, is essential for achieving a high ORR current. This work introduces the direct ammonia nitridation of metal complexes as a promising process for designing metal oxynitride catalysts.

Anisotropic adsorption of xanthate species on molybdenite faces and edges and its implication on the flotation of molybdenite fines

Utilizing xanthate in bulk flotation of Cu-Mo sulfide ores is inevitable, but the implication of xanthate on the flotation of molybdenite fines is barely understood. In this study, the influence of sodium butyl xanthate (SIBX) on the flotation of molybdenite fines and the interaction mechanism was comprehensively investigated by micro-flotation tests, contact angle, adsorption capacity, electrochemical tests, atomic force microscopy (AFM), Fourier Transform Infrared Spectrometer (FTIR), X-ray Photoelectron Spectroscopy (XPS) and density functional theory (DFT) calculations. Micro-flotation tests indicated that SIBX significantly enhanced the flotation of molybdenite fines across a wide pH range. Contact angle, adsorption capacity, Tafel curves, AFM, FTIR and XPS results suggested both xanthate and dixanthogen species adsorbed on molybdenite surfaces, thus improving the hydrophobicity of both edges and faces. Rest potential measurements clarified dixanthogen species dominated on faces while xanthate ions prevailed on edges. DFT calculations elucidated dixanthogen physically adsorbed (−66.06 kJ/mol) on faces while xanthate chemisorbed (−235.62 kJ/mol) on edges via the hybridization of two S atoms within SIBX with two Mo atoms to form highly covalent bonds. This work first clearly unveiled the anisotropic adsorption mechanism of SIBX species on faces and edges, significantly improving the flotation efficiency of molybdenite fines.

Enhanced Chalcopyrite Dissolution in Acidic Culture Medium: The Impact of Arsenopyrite Presence

Nowadays, research on promoting the dissolution of chalcopyrite is important. As a natural symbiotic mineral of chalcopyrite, arsenopyrite will have an impact on the dissolution of chalcopyrite. This paper shows the influence of arsenopyrite on the dissolution of chalcopyrite in an acidic culture medium. The leaching results showed that adding arsenopyrite increased the leaching concentration of copper by 332 mg/L. The residues showed a decrease in sulfur through X-ray diffraction analysis (XRD) and an increase in dissolution degree through scanning electron microscope (SEM). Electrochemical experiments have shown that the rest potential of arsenopyrite is higher than that of chalcopyrite, so there is a galvanic interaction, and the impact on chalcopyrite is greater than that of arsenopyrite. The polarization curve also proves this. Under the interaction of galvanic couples, the reduction of S0 production and the enhancement of Cu2+ release can promote the dissolution of chalcopyrite. In addition, X-ray photoelectron spectrometer (XPS) analysis under the action of galvanic coupling indicates that more SO42− is generated on the surface of chalcopyrite, replacing Sn2−/S0, and SEM shows a stronger corrosion morphology. All results confirm that the electrochemical effect between arsenopyrite and chalcopyrite promotes the dissolution of chalcopyrite in the acidic culture medium.

Gold Recovery from Thiosulfate Leaching Solution Using Silicon Powder and Electrochemical Monitoring of Its Process

Gold recycling from Waste Electrical and Electronic Equipment (WEEE) has been actively conducted. We previously reported a noble metal recovery process using aqua regia and electroless displacement deposition onto silicon powder [1,2]. Using silicon powder has such advantages as that noble metals and copper are selectively recovered, and sawdust silicon, that is, industrial waste silicon powder is available to use. Recently, ammonium thiosulfate solution has attracted attention as a safe and low-cost solution for gold leaching [3-6]. In this study, we successfully recovered gold from an ammonium thiosulfate solution by using silicon powder [7,8], and tried to monitor the recovering behavior electrochemically. Since the ammonium thiosulfate leaching solution includes copper ions as oxidizing agent, copper is recovered by silicon powder. Thus, the monitoring was conducted in order to determine the suitable timing for efficiently obtaining pure gold during the process. For experimentation, an ammonium thiosulfate solution containing gold(I) sulfite and copper(II) sulfate was prepared (pH = 13). We immersed a gold wire in the solution and measured the rest potential during the recovery process using silicon powder. The potential of gold wire shifted stepwise toward negative direction at each start and end of gold and copper recovery. The results suggest that the efficient recovery of high-purity gold can be achieved by monitoring the potential of gold.[1] K. Fukuda, S. Yae, N. Fukumuro, S. Sakamoto, and H. Matsuda, ECS Trans., 53(19), 69 (2013). DOI: 10.1149/05319.0069ecst[2] K. Fukuda, N. Fukumuro, S. Sakamoto, and S. Yae, ECS Trans., 61(10), 1 (2014). DOI: 10.1149/06110.0001ecst[3] M.G. Aylmore and D.M. Muir, Miner. Eng., 14, 135 (2001). DOI: 10.1016/s0892-6875(00)00172-2[4] H. Arima, T. Fujita, and W. Yen, Mater. Trans., 43, 485 (2002). DOI: 10.2320/matertrans.43.485[5] S. Syed, Hydrometallurgy, 115-116, 30 (2012). DOI: 10.1016/j.hydromet.2011.12.012[6] B. Xu, W. Kong, Q. Li, Y. Yang, T. Jiang, and X. Liu, Metals, 7, 222 (2017). DOI: 10.3390/met7060222[7] Y. Iwai, Y. Takashima, A. Matsumoto, and S. Yae, Abst. Interfinish2020 20th world congress, P-E2-001 (2021).[8] Y. Takashima, A. Matsumoto, Y. Iwai, S. Arita, and S. Yae, J. Surf. Finish. Jpn., 73, 98 (2022). DOI: 10.4139/sfj.73.98

Laser Assisted Electrodeposition of Metals and Alloys

Laser sources are extensively used in surface engineering technology and in materials processing. Their high energy density, excellent directionality and monochromaticity makes them ideal for a wealth of potential uses that require the concentration of a significant amount of energy in a small area. From the electrochemical point of view, one of the most interesting applications for lasers is Laser Assisted Electrodeposition (LAE). Indeed, the high energy density transferred by a laser can locally change the electrochemical state of a surface by inducing photo-electrochemical or thermal-electrochemical effects, triggering thus metal reduction. In addition, it is also possible to pattern the deposited metal layer by scanning the surface of the substrate with the laser, usually with spatial resolution in the range of few micrometers. From the applicative point of view, LAE can be exploited for the selective deposition of metal layers for both decorative and functional uses.LAE can be intended in two ways: the laser can be used to enhance a standard electrolytic deposition process [1, 2], increasing deposition rates by focusing the radiation on the cathode, or it can be used to trigger electrodeposition on freestanding metal surfaces in total absence of any external polarization [1]. The latter approach is the most interesting due to the reduced complexity of the setup required and is made possible by the localized variation of the rest potential induced in the zone of the substrate hit by the light [1]. As a consequence of this variation, metallic ions can be reduced in correspondence of the illuminated zone. The occurrence of this phenomenon, which allows metal deposition without any external power source, has been demonstrated for Cu [1, 3], Ni [3] and Au [4].Despite the work carried out by many research groups, still many aspects of LAE in absence of external polarization remain poorly understood. The aim of the present work is to investigate the possibility to perform LAE with some significant metal-substrate couples. The deposition mechanism is rationalized considering the specific electrochemical properties of the metals involved. In addition to this fundamental characterization, the work also aims at evaluating the industrial applicability of LAE. To this extent, patterned layers of precious metals are deposited on metallic substrates for decorative purposes. Finally, LAE is applied here for the first time to the deposition of alloys.[1] J. C. Puippe et al., J. Electrochem. Soc. 128(12), 2539-2545 (1981)[2] Z. Zhang et al., MDPI Materials 13, 3560 (2020)[3] R. J. von Gutfeid et al., IBM J. Res. Develop. 26(2), 136-144 (1982)[4] Khan et al., NASF Surface Technology White Papers 84(3), 6-13 (2019)

History of electrophysiological research from “Animal Electricity” by L. Galvani to electrical potentials by V. Chagovts

The development of physiology as an independent science is closely related to electrophysiology. The regularities formulated in this section are important for understanding the regularities of the functioning of internal organs. The section of electrophysiology includes the study of excitability processes, the formation of rest and action potentials, the mechanisms of muscle contraction, the conduction of excitation along nerve fibers, the mechanisms of conduction of excitation through synapses. The work of all internal organs is based on electrophysiological principles, since excitable tissues are part of the functioning internal organs. Both students of medical universities and working doctors will find it useful to get acquainted with this material, which determines the relevance of the work. We set the aim of the article is to analise the historical stages in the formation of electrophysiology as an independent section of physiology. Metodology of the study is realized mainly with the help of descriptive and historical methods. The novelty of the study. The article states that the presence of “animal electricity” was first noticed by Luigi Galvani. Further studies conducted by Volt, Matteucci, Dubois-Raymond expanded the understanding of the mechanisms of conducting excitations on the neuromuscular elements of the body. Attention is drawn to the role of Ukrainian physiologists who made an important contribution to the scientific heritage. Thus, V. Chagovts discovered the fundamental laws of potential formation and the basis of excitability, the concept of a critical level of depolarization. Conclusions. The resulting patterns are fundamental even today. The data presented in the article expand knowledge of the physiology of excitable tissues and provide an opportunity to form a more complete picture from this section.

A rest potential study of impurity (As, Au, Ni and Co) bearing synthetic pyrite in alkaline flotation conditions

Pyrite is an important mineralogical component of most sulphide ore deposit classes, where it commonly forms part of the gangue mineralogy, but may also represent an important ore mineral (i.e., auriferous pyrite). Effective and efficient separation of pyrite is thus a crucial step during most ore processing operations, and this is in part influenced by the pyrite mineral chemistry. Here, electrochemical measurements were used to study the reactivity of a series of well-characterised synthetic trace-element substituted pyrite samples under alkaline conditions relevant to industrial flotation. The presence of metals and metalloid impurities (As, Au, Co, and Ni) in pyrite were tested using rest potential measurements to infer oxidation and associated hydrophobicity. In the absence of any collector phases, pure- and Ni-substituted pyrite have the highest rest potential, followed by Co-substituted pyrite and couple-substituted (Co + Au) pyrite, whilst As-substituted pyrite has the lowest measured rest potential. Importantly, the degree of oxidation at the mineral surface correlates linearly with the concentration of each of the substituents, with the largest effect observed when As is the substituent. These results correspond to the semiconducting properties and noble character of each pyrite sample, with n-type pyrite (Au-, Co- and Ni-substituted) associated with noble character and high rest potential, whereas p-type As-substituted pyrite associated with least noble character and lowest rest potential. With the addition of a potassium amyl xanthate collector, the mineral chemistry further had an impact on the probability of dixanthogen formation. Increased substituent concentration in the pyrite lattice decreased the probability of dixanthogen formation, except in a sample where high Au (and moderate Co) was incorporated. These results highlight the importance of developing improved understanding of the impacts of substitution mechanisms on the surface reactivity and flotability of pyrite. Such an understanding will form the foundation for further improved (and engineered) approaches towards reagent design and mixture. This will serve to optimise separation of both gangue and valuable pyrite by using fundamental knowledge to target specific collector bands and flotation domains.

A novel recycling route for aluminum alloys: Synthesis of Fe/Al bimetallic materials and magnetic separation

Aluminum (Al) is one of the most important non-ferrous metals used in modern society, but its production from primary ores (e.g., bauxite) requires high energy input, emits large CO2, and generates huge amounts of solid wastes. In contrast, the production of Al from recycled scrap—also known as secondary Al production—only requires 5–8% of the energy for producing Al from bauxite and generates less amount of solid waste than that of the primary Al production, thus having both economic and environmental benefits. In general, scrap Al alloys are treated by physical-based separation techniques to remove impurities, and then mixed aluminum alloys are charged into the furnace for further refining. The ideal way of recycling Al scrap is to process each Al alloy by remelting/refining processes. To this end, this study investigated the surface modification of aluminum alloys by iron (Fe) deposition, followed by their separation by magnetic separation.When Al powder was treated with an acidified ferrous chloride solution (FeCl2-HCl-NaCl solution), dissolved Fe concentration decreased with time while releasing Al3+ into the solution, indicating that Fe cementation on Al occurred. X-ray photoelectron spectroscopy (XPS) analysis of treated Al powder showed that its surface was covered with zero-valent iron (ZVI) as well as its oxidation products (e.g., Fe(II)/Fe(III)-oxyhydroxide). The synthesis of Fe/Al bimetallic materials from Al alloys—1050, 2024, 3003, 5083, 6061, and 7075—was strongly dependent on HCl concentration as well as reaction temperature. Moreover, the kinetics of Fe cementation on Al alloys and the amounts of Fe cemented were determined not only by the rest potentials of the Al alloys but also their corrosion resistance. After treating Al alloys with FeCl2-HCl-NaCl solution, each Al alloy could be sequentially recovered by magnetic separation.

Investigating the Influence of the Electrochemical Environment on the Flotation of Bornite and Chalcocite

Beneficiation of sulphide ores by flotation is ascribed to the natural electrochemical activity associated with sulphide minerals. Flotation is an electrochemical process comprising many interdependent conditions that are difficult to decouple in terms of controlling flotation performance. The extent of electrochemical activity is mineral dependent and can be measured against a reference cell to differentiate between minerals. This difference in activity is known as the rest potential. The rest potential can be exploited to preferentially float one mineral over another as these properties result in different regions of flotation stability for different minerals. Bornite and chalcocite present an interesting study because when measured against the standard hydrogen electrode (SHE), there is a small difference in rest potential; bornite has a potential of 0.44 V and chalcocite a potential of 0.40 V. The key differentiating factor between the two minerals is the presence of iron in bornite (Cu5FeS4) and the lack thereof in chalcocite (Cu2S). This study considers bornite and chalcocite microflotation, adsorption studies and zeta potential measurements, and three key factors were explored: pH, galvanic interactions and collector adsorption. The overall objective of the study is to understand the response of bornite and chalcocite to changes in pulp chemistry.

The Electrochemical Response of Chalcopyrite and Galena to Degrading Water Quality

Water is used as a liquid medium as well as a means of transportation during mining operations. Flotation, in particular, is a water intensive process where water makes up about 80–85% of the pulp phase. Process water contains organic and inorganic species which accumulate as they are recycled. To avoid the treatment costs of removing these contaminants, many mining operations allow the quality of their water to degrade over time. When this water is introduced into flotation circuits, the pulp chemistry is altered. Ionic species that accumulate in recycled process water have been shown by previous studies to be especially deleterious to flotation performance. Such ions include Ca2+, Cu2+, Mg2+, Pb2+, SO42− and S2O32−, amongst others. The flotation sub-process of collector adsorption which is responsible for inducing hydrophobicity on valuable mineral surfaces may be influenced by water chemistry. Accumulating ionic species have been shown to hinder collector adsorption which may reduce recovery of valuable minerals to the concentrate. Consequently, degrading water quality may threaten the economic viability of mining operations that make use of closed water circuits. Electrochemical techniques such as mineral rest potentials can be used to monitor the impact of changing water quality on collector–mineral interactions. Microflotation was used to determine whether mineral floatability was affected by changing water quality. This study therefore aimed to investigate whether electrochemical techniques such as rest potential measurements can be used to predict flotation performance under changing water quality. No definable relationship was found between the rest potential differences and the microflotation initial recoveries, however, rest potential measurements did identify the negative impact that thiosulphate ions may have on flotation processes.

Galvanic effect of magnetite on electrochemical oxidation of arsenopyrite in acidic culture medium

The galvanic interaction of arsenopyrite—magnetite in acidic culture medium was investigated by electro- chemical measurements, X-ray photoelectron spectroscopy characterization and leaching experiments. The results indicated that the rest potential of magnetite was 321 mV, which was more anodic than 223 mV of arsenopyrite, and the galvanic current was 7.40 µA, verifying the existence of the galvanic interaction between arsenopyrite and magnetite. The galvanic potential and polarization curves suggested that the redox behaviors of arsenopyrite dominated the overall galvanic interaction. The galvanic interaction enhanced the electrochemical dissolution of arsenopyrite with the generation of more oxidation products (S0, SO32—, SO42— and AsO33—) on arsenopyrite and an increase in the chemical reactivity of the surface. Leaching experiments of 6 days showed that the presence of magnetite improved the arsenic release from arsenopyrite by 30 mg/L, and further confirmed the enhanced oxidation of arsenopyrite when coupled with magnetite.

Optimization of Pulsed Polarization Condition for Efficient Electrochemical CO2 Reduction

Introduction Massive emission of CO2 gas from fossil fuel combustion causes the severe global greenhouse effect. Electrochemical reduction of CO2 using renewable energy has been attractive due to its simple methodology, while the conversion efficiency may be lessened due to undesirable side reactions such as water decomposition. In this study, CO2 was covered to CO on Ag electrode in aqueous KHCO3 solution using potentiostatic pulse polarization, and optimal pulse condition to improve the conversion efficiency was explored. Experiment An electrochemical cell was composed of a cathode compartment containing an Ag working electrode (W.E.) and an Ag/AgCl reference electrode and an anode compartment containing a Pt counter electrode. Two compartments were separated by a Nafion membrane. An Ag-W.E. was mechanically polished and potentiostatically pulse-polarized in a CO2-saturated 0.1 M KHCO3 solution to form CO. After some polarization period, the conversion efficiency ( η=[CO]/([CO]+[H2]) ) of CO2 to CO was evaluated by using gas chromatography as a function of various parameters such as cathodic polarization potential (E c) and time (t c), rest potential (E a) and time (t a), KHNO3 concentration, etc. Result and discussion When E c was varied, the highest η was obtained around –1.5 to –1.6 V. When t c was varied at E c = –1.6 V, the highest η was obtained around t c = 3 s, as shown in Fig. 1. The t a did not affect η. These results reveal that the t c influences the conversion efficiency viacontrolling the diffusion layer thickness of reactants such as CO2 molecular. The highest η at the optimal pulse condition was ca. 0.9 and is comparable to the value obtained by the previous work using ionic liquid solution (T. Oguma et al., Electrochemistry, 88 (2020) 451–456). Fig. 1. Relationship between the cathodic polarization time t c and reduction efficiency Figure 1

Sulfur Composite Cathodes for High-Capacity Aluminum Metal Anode Rechargeable Batteries

Recently, needs to rechargeable batteries have been diversified into various kinds due to expansion of their application range. Not only future high-performance batteries exceeding Li-ion batteries (LiBs), but also new concept ones, which are composed solely of common elements and have performance comparable to current LiBs, have become one of the important recent research targets in this area. Focusing rich abundance and very-high theoretical capacity (2980 mAh g-1, 8046 mAh cm-3) of aluminum (Al) metal, we have created new concept rechargeable batteries with the following anode reaction in chloroaluminate ionic liquids (ILs):1,2 4[Al2Cl7]- + 3e- ⇌ Al + 7[AlCl4]- Many research groups have also reported similar Al metal anode batteries.3 Herein, some sulfur (S) composite cathodes that enable the use of S(IV)/S electrode reaction are designed to greatly enhance the capacity of Al metal anode battery.The preparation and purification processes for 60.0-40.0 mol% AlCl3–[C2mim]Cl and 61.0-26.0-13.0 mol% AlCl3–NaCl–KCl IL electrolytes were identical with those described in our previous articles.1,2 Three types of cathode active materials, S-coated multi-walled carbon nanotube (S-MWCNT), sulfurized polyethylene glycol (SPEG),4 and sulfurized polyacrylonitrile (SPAN),5 were employed. All the S composite electrodes were prepared by pressing the mixtures of 50 wt% S-based cathode active materials, 45 wt% conductive additive (MWCNT), and 5 wt% polytetrafluoroethylene onto Mo plate current collectors. Al metal plate was employed as the anode active material. Electrochemical experiments were carried out with a commonly used three-electrode cell or a two-electrode sealed cell in an Ar gas-filled glove box with O2 and H2O < 1 ppm.Figure 1 shows multiple cyclic voltammograms recorded at a S-MWCNT composite electrode in a three-electrode cell with 60.0-40.0 mol% AlCl3–[C2mim]Cl at 298 K. When the potential scan was initiated from the rest potential to the negative direction, a pair of reduction and oxidation waves appeared with large over potential. These waves gradually varied with an increase in the number of cycles. Considering the article reported by Gao et al.,6 the redox waves observed in Fig. 1a can be regarded to be the following electrochemical reaction (S/S2-):3S + 8[Al2Cl7]- + 6e- ⇌ Al2S3 + 14[AlCl4]- As for the positive scan from the rest potential (Fig. 1b), several oxidation and reduction waves were observed. Overpotential obviously diminished compared to that for the S/S2-. Similar electrode behavior for S in a Lewis acidic 63-37 mol% AlCl3–NaCl molten salt is reported by Marassi, et al.7 Given that the electrochemical reaction process is the same, the number of electrons involved in the reaction is estimated to be 4. Then, the electrochemical reaction (S(IV)/S) is:[SCl3]+ + 3[Al2Cl7]- + 4e- ⇌ S + 6[AlCl4]- If we can apply this S(IV)/S reaction to the Al metal anode-S cathode rechargeable battery, S cathode capacity becomes double and higher working voltage is expected relative to conventional S/S2- one. Unfortunately, the redox waves for the reaction decrease sharply with increase in the cycle number. The waves almost disappeared at the 5th cycle. Analogous results were also obtained in the 61.0-26.0-13.0 mol% AlCl3–NaCl–KCl. We concluded that the electrode reaction for S(IV)/S on the S-MWCNT composite cathode is not suitable for battery application. However, the use of S-combined active materials, SPEG and SPAN, substantially improved the electrode reaction in the 61.0-26.0-13.0 mol% AlCl3–NaCl–KCl IL at 393 K. Thus, we carried out the charge-discharge test for the Al | SPEG and Al | SPAN batteries with the inorganic IL electrolyte using both S/S2- and S(IV)/S electrode reactions. If SPEG was used, the discharge capacity was ca. 1050 mAh (g-S)-1 at 50th cycle. When using only S/S2- reaction, such high capacity was not attained.2 The S(IV)/S electrode reaction should be directly involved in the capacity increase. Interestingly, the use of SPAN made further improvement possible. One of the typical results is shown in Fig. 2. At the first cycle, the discharge capacity reached ca. 4700 mAh (g-S)-1 and showed ca. 2600 mAh (g-S)-1 even after 50th cycle. These results suggest that the S-combined active material, i.e., SPEG and SPAN, composite electrodes can work as the high-capacity cathodes for Al metal anode rechargeable battery.This research was supported by JST-MIRAI program (JPMJMI17E9). SPAN was provided by ADEKA corporation. References Tsuda, et al., J. Electrochem. Soc., 161, A908 (2014).Tsuda, et al., Chem. Commun., 58, 1518 (2022).Ru, et al., J. Mater. Chem. A, 7, 14391 (2019).Kojima, et al., ECS Trans., 75, 201 (2017).S. Ahmed, et al., Adv. Sci., 8, 2101123 (2021).Gao, et al., Angew. Chem. Int. Ed., 55, 9898 (2016).Marassi, et al., J. Electrochem. Soc., 126, 231 (1979). Figure 1

(Invited) Effect of Electrochemical Treatment and pH on VIV/VV Electrode Kinetics

Flow batteries are a promising technology for flexible large-scale energy storage systems to tackle the problem of intermittency with renewable energy sources. Several flow battery systems have been successfully developed and deployed to date, including all-vanadium, zinc-iron, zinc-bromine, and all-iron flow batteries.1 Among these, vanadium flow batteries (VFBs) have received a lot of attention in the large-scale energy storage sector due to their excellent characteristics such as long cycle life with almost zero electrode and electrolyte degradation, safe and non-flammable aqueous electrolytes, short response times, and the ability to operate at reasonable temperatures.2 The operation of flow batteries involves simultaneous oxidation and reduction reactions at the anodic and cathodic compartments. In the VFB, the redox couple at the anode is VII-VIII and at the cathode is VIV-VV.Voltage inefficiencies at the electrode-electrolyte interface are a source of concern for the operation of these systems.3 Electrode polarization, slow kinetics, and iR losses associated with contact and ionic resistances all contribute to battery voltage inefficiencies. It is widely acknowledged that the electrode material and pretreatments (chemical, thermal, and electrochemical) have significant impacts on the electrode kinetics and hence the performance of the VFB system.4 Investigation of the electrode kinetics is thus important in order to better understand and improve the performance of VFBs.Previous research from our group has shown that electrochemical treatments of carbon electrodes at different potentials significantly affect the electrode kinetics of VIV-VV and VII-VIII oxidation-reduction reactions. The electrode kinetics of VIV-VV are enhanced by cathodic treatment of the electrode and inhibited by anodic treatment. In contrast, the electrode kinetics of VII-VIII are enhanced by anodic treatment of the electrode and inhibited by cathodic treatment. Furthermore, the carbon electrode can be toggled repeatedly and reproducibly between the enhanced (activated) and the inhibited (deactivated) state.5,6,7 Other factors affecting the electrode activity include ageing of the electrode, the final treatment potential, the redox rest potential, and the treatment potential window.8 This previous research involves treatments in strong acid, low pH electrolytes.In this study, we investigate the electrochemical treatment of glassy carbon electrodes in electrolytes at a range of pH. The resulting electrode kinetics of the vanadium redox couples at each treatment potential are studied using electrochemical characterization techniques including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Acknowledgements Varsha Sasikumar S P would like to thank the Irish Research Council (IRC) for providing funding for this research work. References Xinyou Ke et al., Chemical Society Reviews, 47, 8721-8743 (2018).R. Chalamala et al., Proceedings of the IEEE, 102(6), 976-999, (2014).A. H. Whitehead and M. Harrer, Journal of Power Sources, 230, 271–276 (2013).Ki Jae Kim, et al., Journal of Materials Chemistry A, 33(3), 16913-16933 (2015).A. Bourke et al., Journal of Electrochemical Society, 163, A5097 (2016).A. Bourke et al., Journal of Electrochemical Society, 162, A1547 (2015).M. A. Miller, et al., Journal of Electrochemical Society, 163, A2095-A2102, (2016).D. N. Buckley, et al., ECS Transactions, 98(9), 223-239 (2020).

CHANGES IMPACT ON THE DEVELOPMENT POTENTIAL OF THE ENTERPRISE

The article examines the impact of changes on the development potential of the enterprise. Possible reactions to changes are considered in detail. The definition of resting potential and action potential is given. Rest potential is not a static indicator of enterprise development, but has a slower pace than action potential. We know that all enterprises are in constant search and improvement, even crises can be perceived as an impetus to action. The authors identified the need to take into account changes in the external environment and the inverse reaction to the external environment, the strength of the impact of changes on the enterprise development potential. The relationship between changes and the potential of the enterprise is identified through a system of sets that helps to establish the relationship and consistency of factors influencing changes, taking into account cross-influences. Among the main factors, we will pay attention to the following: organization, personnel, marketing, technology, novelty degree of equipment and technologies, product update frequency, availability of patents and licenses, product, resources, finances, organizational culture, as well as the main characteristics of the external environment: complexity, mobility, uncertainty and interrelationship of factors. We proposed to use mathematical functions and tuples of the full combination to describe the relationship between changes and enterprise development potential.

Effective Use of Sacrificial Zinc Anode as a Suitable Repair Method for Severely Damaged RC Members Due to Chloride Attack

In many cases, the repair strategy by using sacrificial anodes for cathodic protection in real RC structures requires additional zinc anodes after several years due to the decreasing protective area. This experimental study evaluates the effectiveness of time lag application of sacrificial anode cathodic protection applied to RC beam specimens that deteriorated severely due to chloride attack. In the experiment, sacrificial anodes and cathodic protection (SACP) were applied to 41-year-old RC beam specimens exposed to natural marine environments in which the embedded steel bars were significantly corroded. The repair work was performed in three stages. Instant-off and rest potential tests of steel bars were conducted periodically to demonstrate the time-dependent depolarization value. In the first stage, a polymer-modified mortar as a patch repair material was cast to replace the concrete in the middle tensile part with small sacrificial anodes embedded in the mortar. After the protective current reaches an equilibrium state, the sacrificial anodes are disconnected from the steel bars for a year, defined as the second stage. During the one year in the second stage, the steel bar in the patch repair area remained passive, without any sign of corrosion. As for the third stage, additional sacrificial anodes were installed in the existing concrete part to protect the steel in it. From one year of observation after applying sacrificial anodes to old concrete parts, the time lag SACP application of both in patch and non-patch repair parts was clarified to be effective in stopping the corrosion of steel bar in both parts until 20–30 years based on the service life prediction. Doi: 10.28991/CEJ-2022-08-07-015 Full Text: PDF

Synthesis and Characterization of Polypyrrole Film Doped with Both Molybdate and Salicylate and Its Application in the Corrosion Protection for Low Carbon Steel.

Polypyrrole (PPy) films doped with molybdate and salicylate have been successfully electropolymerized on low carbon steel in aqueous solutions containing both molybdate and salicylate in a one-step process that did not require any pre-treatment of the steel substrate. Salicylate-doped PPy films were synthesized in the same way for comparison. The steel surface was rapidly inhibited and the PPy-based films were formed on it easily. The PPy-based films were characterized by Fourier transform infrared, scanning electron microscopy, energy dispersive X-ray, and thermal gravimetric analysis methods. The corrosion protection performance of the coatings was investigated with electrochemical impedance spectroscopy, open circuit potential (OCP), salt spray test, and Tafel polarization. It was found that in the presence of both molybdate and salicylate as dopants, the films on steel could present a better corrosion resistance than PPy film doped with only salicylate. The self-healing property of PPy-based films was observed on the OCP measurement with the fluctuation of rest potential. The salt spray test results showed that the PPy film doped with both salicylate and molybdate was more salt-resistant than the PPy film doped with only salicylate. The results suggest that the PPy coatings doped with both molybdate and salicylate are potential for application as metallic anti-corrosion coatings.

Carbon fibre-supported hierarchical NiCo layered double hydroxide nanosheets as non-enzymatic glucose sensors for sport drinks and serum

We report a systematic study of carbon fibre (CF)-supported NiCo layered double hydroxide nanosheets (LDHNs) with and without heat treatment at 200 and 400 °C (CF-NiCo LDHN200 and CF-NiCo oxide nanoparticles (NPs), respectively) as catalysts and sensors for glucose oxidation reactions (GORs). Tafel measurements for the GORs showed that the exchange current density of CF-NiCo LDHN was 1.91 × 10−3 mA·cm−2 at an early rest potential of −0.422 V. This was markedly higher than those of CF-NiCo LDHN200 (1.22 × 10−3 mA·cm−2 at − 0.352 V) and CF-NiCo oxide NP (1.18 × 10−3 mA·cm−2 at −0.327 V). The electron transfer number and Tafel slopes suggested that the glucose dehydrogenation step and one-electron release occurred first in the GORs. Amperometric measurements revealed high recoveries (101.92% and 98.92%) and low relative standard deviations (1.98% and 2.34%) for the determination of glucose using the CF-NiCo LDHN in sports drink samples and human serum.

Electrochemical Study on Hydrogen Entry Initiationin SSRT of Low Alloy Steel in High-Pressure Hydrogen Gas

The application of concurrent cathodic hydrogen charging SSRT is being investigated as an alternative to SSRT in high-pressure hydrogen gas, which is used to evaluate the hydrogen compatibility of metallic materials. There are some differences in the stress-displacement behavior and the fracture surface between the two tests. These differences can be attributed to the difference in the timing of the onset of hydrogen entry in the two environments. In SSRT of low-alloy steel in high-pressure hydrogen gas, the amount of absorbed hydrogen up to the yield stress is small and increases rapidly after plastic deformation, Whereas, since in concurrent cathodic hydrogen charging, hydrogen entry is initiated as soon as begins, it is necessary to determine an apporopriate start time. The surface changes of SCM435 specimens during SSRT in NaOH solution were analyzed by electrochemical measurements, and the breakdown of the oxide film that inhibits hydrogen entry during SSRT in high-pressure hydrogen gas was discussed. As a result, the impedance at low frequencies decreased immediately after the yield point, which was attributed to the decrease in the reaction resistance of the oxide film. The rest potential decreased immediately after the yield point and immediately after the fracture, which were attributed to the exposure of the fresh surface due to the breakdown of the oxide film. From these results, it was clear that hydrogen charging in the concurrent cathodic hydrogen charging SSRT should be started just after the yield point.

Electrochemical study on molten iron-carbon electrodes in slag and their decarburization by slag/metal reaction

An electrochemical study on molten iron-carbon electrodes in slag and their decarburization during anodic polarization was performed at 1600 °C to obtain information relevant to steelmaking. Carbon concentration was varied from 4.5 to 0.2 wt% to cover the range of interest between pig iron tapped from blast furnaces and steel tapped from oxygen converters or electric arc furnaces. Impedance spectra were measured at the rest potential and at applied direct current biases, and results were fitted to a faradaic decarburization reaction proceeding through two adsorbed intermediates. At the rest potential, carbon significantly increases faradaic activity at the metal/slag interface as evidenced by a strong increase in exchange current and interfacial capacitance with carbon activity. The apparent standard heterogeneous rate constant of the anodic decarburization half-cell was determined using the dependence of exchange current on carbon activity. During electrochemical decarburization, interfacial capacitance decreases significantly which is consistent with changes in surface concentrations of intermediates. Using a comprehensive kinetic model, surface concentrations of intermediate adsorbed species were determined during anodic polarization in the Tafel region. Results from impedance spectroscopy were compared with those obtained by gas chromatography during constant-current decarburization.