Extended Potential Range Research Articles

Exploring the electrochemical utilization of PANI/CNT-integrated Ni-Mn phosphates for advanced supercapacitor applications

The increasing need for high-performance energy storage systems necessitates the exploration of novel electrode materials. In this study, the utilization of polyaniline/multiwalled carbon nanotubes (PANI/MWCNTs) was demonstrated as a conductive scaffold for the formation of heterostructures comprising nickel manganese phosphate (NiMn(PO4)2) using probe sonication, leading to the development of an efficient hybrid supercapacitor. The PANI/MWCNTs composite exhibits favorable conductive properties, acting as a suitable framework for the nucleation/growth and integrating NiMn(PO4)2 structures. The synergistic combination of PANI/MWCNTs and NiMn(PO4)2 resulted in the development of a highly efficient hybrid anode, exhibiting a remarkable specific capacitance of 917.3 F g‐1 (912.2 C g−1) at 1 A g‐1 in a 1 M KOH electrolyte. The optimized composite, PCNT-NMP-40, as a positive electrode in a two-electrode cell configuration with activated carbon (AC) as the negative electrode, operates within an extended output potential range of 0–1.6 V in a 2 M KOH electrolyte, delivering an outstanding energy density of 58 Wh kg−1 and a power density of 918 W kg−1, reflecting the substantial potential use of PCNT-NMP-40 as an excellent candidate for advanced energy storage applications.

Ligand field regulation of δ-MnO2 by polyanion modification enables extended potential window in supercapacitors

Extending the potential range of MnO2 is imperative to improve power density and capacity density for supercapacitors. However, MnO2 usually suffers from severe Mn dissolution, irreversible phase transition, and poor cycling performance under an extended potential range. Herein, a ligand field regulation strategy is rationally designed to enhance the structural stability of δ-MnO2 to extend the potential window to 0–1.3 V (vs. Ag/AgCl). As revealed, the generated strong covalent B–O plane triangle or P–O tetrahedron configuration effectively decreases the lattice O activity of δ-MnO2. The B–O–Mn and P–O–Mn bonding interactions enhance Mn ion crystal field stabilization energy in the MnO6 octahedra. Therefore, the lattice O loss, Mn dissolution, and irreversible phase transition are well suppressed. The PO43− doped δ-MnO2 electrodes (with a high mass loading of ∼10 mg cm−2) can deliver a large specific capacitance (268.3 F g−1 at 0.5 A g−1) and excellent cycling performance (83.5% after 10000 cycles) in the extended potential window of 0–1.3 V (vs. Ag/AgCl). Our ligand field regulation strategy affords opportunities for developing simultaneously high-capacity and high-voltage electrodes for supercapacitors.

Optimal Pt-Au Alloying for Efficient and Stable Oxygen Reduction Reaction Catalysts.

Stabilization of cathode catalysts in hydrogen-fueled proton-exchange membrane fuel cells (PEMFCs) is paramount to their widespread commercialization. Targeting that aim, Pt-Au alloy catalysts with various compositions (Pt95Au5, Pt90Au10, and Pt80Au20) prepared by magnetron sputtering were investigated. The promising stability improvement of the Pt-Au catalyst, manifested in suppressed platinum dissolution with increasing Au content, was documented over an extended potential range up to 1.5 VRHE. On the other hand, at elevated concentrations, Au showed a detrimental effect on oxygen reduction reaction activity. A systematic study involving complementary characterization techniques, electrochemistry, and Monte Carlo simulations based on density functional theory data enabled us to gain a comprehensive understanding of the composition-activity-stability relationship to find optimal Pt-Au alloying for maintaining the activity of platinum and improving its resistance to dissolution. According to the results, Pt-Au alloy with 10% gold represent the most promising composition retaining the activity of monometallic Pt while suppressing Pt dissolution by 50% at the upper potential limit of 1.2 VRHE and by 20% at devastating 1.5 VRHE.

Титанат лития, допированный неодимом, как анодный материал для литий-ионных аккумуляторов

Doped lithium titanate is known to be able to reversibly cycle in the potential range from 3 to 0.01 V and this ability depends both on the nature of the dopant and the doping level. In this work Li4Ti5O12 samples doped with Nd in the amount of 0.5 to 2.0% were studied. It was shown that while being cycled in the extended potential range, the samples with the doping level from 0.5 to 1.0% demonstrated the highest capacity.

Eliminating dissolution of platinum-based electrocatalysts at the atomic scale.

A remaining challenge for the deployment of proton-exchange membrane fuel cells is the limited durability of platinum (Pt) nanoscale materials that operate at high voltages during the cathodic oxygen reduction reaction. In this work, atomic-scale insight into well-defined single-crystalline, thin-film and nanoscale surfaces exposed Pt dissolution trends that governed the design and synthesis of durable materials. A newly defined metric, intrinsic dissolution, is essential to understanding the correlation between the measured Pt loss, surface structure, size and ratio of Pt nanoparticles in a carbon (C) support. It was found that the utilization of a gold (Au) underlayer promotes ordering of Pt surface atoms towards a (111) structure, whereas Au on the surface selectively protects low-coordinated Pt sites. This mitigation strategy was applied towards 3 nm Pt3Au/C nanoparticles and resulted in the elimination of Pt dissolution in the liquid electrolyte, which included a 30-fold durability improvement versus 3 nm Pt/C over an extended potential range up to 1.2 V.

Voltammetric Study of Tin Electrodeposition on Polycrystalline Gold from Sulfuric and Methanesulfonic Acid

In this work, we have studied tin electrodeposition on polycrystalline gold electrodes from two different supporting electrolytes: sulfuric acid (SA) and methanesulfonic acid (MSA), both of them commonly used in the industry. This work aims to understand the effect of the different electrolyte anions on the deposition process. We show at least three different tin deposition mechanisms on gold: irreversible adsorption, underpotential deposition, and overpotential (bulk) deposition. Underpotential deposition leads to the formation of a layer of tin in SA and MSA with a coverage around ML (monolayer) and ML, respectively. The UPD Sn layer is however somewhat uncharacteristic as it is associated with island formation and surface alloying. Cyclic voltammograms in an extended potential range showed five distinct peaks: two cathodic peaks associated with tin underpotential and overpotential deposition, and three main anodic peaks, corresponding to the oxidation of the bulk Sn, of the AuSn intermetallic layer, and of the adsorbed Sn(II) to Sn(IV). Both voltammetric and rotating disk electrode measurements show that the kinetics of tin electrodeposition in MSA is slower than in SA, which we ascribe to Sn-MSA complex formation in solution. Slow Sn deposition in MSA promotes AuSn formation, in contrast to SA in which bulk tin deposition is more prominent. Complete Levich-type mass transport control of tin deposition in SA and MSA was only reached at low scan rate due to concurrent HER on the uncovered gold surface during the deposition process at higher scan rates. An unexpected surface-confined passivation process is observed in both electrolytes.

Na+/Vacancy Disordered P2-Na0.67Co1-xTixO2: High-Energy and High-Power Cathode Materials for Sodium Ion Batteries.

Although sodium ion batteries (NIBs) have gained wide interest, their poor energy density poses a serious challenge for their practical applications. Therefore, high-energy-density cathode materials are required for NIBs to enable the utilization of a large amount of reversible Na ions. This study presents a P2-type Na0.67Co1-xTixO2 (x < 0.2) cathode with an extended potential range higher than 4.4 V to present a high specific capacity of 166 mAh g-1. A group of P2-type cathodes containing various amounts of Ti is prepared using a facile synthetic method. These cathodes show different behaviors of the Na+/vacancy ordering. Na0.67CoO2 suffers severe capacity loss at high voltages due to irreversible structure changes causing serious polarization, while the Ti-substituted cathodes have long credible cycleability as well as high energy. In particular, Na0.67Co0.90Ti0.10O2 exhibits excellent capacity retention (115 mAh g-1) even after 100 cycles, whereas Na0.67CoO2 exhibits negligible capacity retention (<10 mAh g-1) at 4.5 V cutoff conditions. Na0.67Co0.90Ti0.10O2 also exhibits outstanding rate capabilities of 108 mAh g-1 at a current density of 1000 mA g-1 (7.4 C). Increased sodium diffusion kinetics from mitigated Na+/vacancy ordering, which allows high Na+ utilization, are investigated to find in detail the mechanism of the improvement by combining systematic analyses comprising TEM, in situ XRD, and electrochemical methods.

Understanding the Behavior of LiCoO2 Cathodes at Extended Potentials in Ionic Liquid–Alkyl Carbonate Hybrid Electrolytes

The current electrolyte compositions makes it hard to achieve a high energy density lithium-ion battery based on LiCoO2 chemistry due to the destabilization of the LiCoO2 crystal structure beyond 4.2 V vs Li/Li+ leading to oxygen evolution and electrolyte decomposition. Therefore, electrolyte developments may hold promise for improved performance, for example, if some of the advantageous properties of ionic liquids can be introduced into a carbonate electrolyte system. Here, we report the use of a hybrid electrolyte (HE) system with a LiCoO2 cathode and have observed an excellent electrochemical performance when cycled to 4.4 V vs Li/Li+. This extended potential range produces higher capacity via greater ion insertion/extraction and better structural stability. A discharge capacity of 161 mAh/g (0.7 lithium extraction) was observed in the HE as compared to 128 mAh/g in conventional electrolyte, after 60 cycles. The charge–discharge studies at extended potentials also indicate better capacity retention in ...

New high-capacity anode materials based on gallium-doped lithium titanate

New anode materials based on gallium-doped lithium titanate were obtained. Doping leads to an increase in the capacity of lithium titanate and its cycling stability in an extended potential range from 0.01 to 3 V.

Corrosion and electrochemical behavior of nanoscale carbon layers deposited onto a surface of nonalloyed steel via pulsed laser deposition

Carbon films 5 to 7 nm thick with a graphite structure are obtained via high-speed laser exposure of ultrafine graphite powder distributed homogeneously on the surface of nonalloyed steel. Due to the created intermediate layer consisting of nonstoichiometric iron carbides, the obtained films have a high adhesion to the substrate. These films also exhibit high continuity and behave as ideally polarizable electrodes over an extended potential range in borate buffer solutions. Cathode and anode currents are much lower in the obtained graphite films than are those measured at the compact graphite materials. The deposited graphite layers completely stop the anodic dissolution of a steel substrate.

P3-Type Layered Sodium-Deficient Nickel-Manganese Oxides: A Flexible Structural Matrix for Reversible Sodium and Lithium Intercalation.

Sodium-deficient nickel-manganese oxides exhibit a layered structure, which is flexible enough to acquire different layer stacking. The effect of layer stacking on the intercalation properties of P3-Nax Ni0.5 Mn0.5 O2 (x=0.50, 0.67) and P2-Na2/3 Ni1/3 Mn2/3 O2 , for use as cathodes in sodium- and lithium-ion batteries, is examined. For P3-Na0.67 Ni0.5 Mn0.5 O2 , a large trigonal superstructure with 2√3 a×2√3 a×2 c is observed, whereas for P2-Na2/3 Ni1/3 Mn2/3 O2 there is a superstructure with reduced lattice parameters. In sodium cells, P3 and P2 phases intercalate sodium reversibly at a well-expressed voltage plateau. Preservation of the P3-type structure during sodium intercalation determines improving cycling stability of the P3 phase within an extended potential range, in comparison with that for the P2 phase, for which a P2-O2 phase transformation has been found. Between 2.0 and 4.0 V, P3 and P2 phases display an excellent rate capability. In lithium cells, the P3 phase intercalates lithium, accompanied by a P3-O3 structural transformation. The in situ generated O3 phase, containing lithium and sodium simultaneously, determines the specific voltage profile of P3-Nax Ni0.5 Mn0.5 O2 . The P2 phase does not display any reversible lithium intercalation. The P3 phase demonstrates a higher capacity at lower rates in lithium cells, whereas in sodium cells P3-Nax Ni0.5 Mn0.5 O2 operates better at higher rates. These findings reveal the unique ability of sodium-deficient nickel-manganese oxides with a P3-type structure for application as low-cost electrode materials in both sodium- and lithium-ion batteries.

A Study of Pt Dissolution during Formic Acid Oxidation

The studies on Pt or Pt-alloy based catalysts for formic acid oxidation (FAO) have been focused mostly on their activity with little analysis of durability and long-term performance. While durability of Pt-based FAO catalysts has been associated with CO poisoning, recent studies have brought evidence of correlation between catalyst performance and dissolution of Pt. Aimed at assessing the impact of that correlation, a detailed quantitative durability analysis of Pt ultrathin films grown on Au by surface limited redox replacement of a Pb underpotentially deposited layer is presented in this work. Long-term catalytic performance of those films featuring well-defined thickness and structure has been examined by potential cycling in 2 M HCOOH+0.1 M HClO4 solution at sweep rate of 0.050 V s–1 over an extended potential range limited positively by the onset of Pt oxidation. A clear proportionality between overall life and thickness of the catalyst observed in the tests emphasizes the dissolution of Pt as the ke...

Electrochemical preparation and characterization of a cobalt oxide–platinum composite with promising capacitive and electrocatalytic features

In the present work, boron-doped diamond polycrystalline films were used as support for direct anodic deposition of the cobalt oxide, and continuous Co3O4 coatings with reasonably good conductivity were obtained by appropriately adjusting the deposition charge. Further electrochemical deposition of platinum particles on the oxide substrate enabled the formation of a stable composite with a specific capacitance of ca. 431 F cm−3 that compares well with that available with similar materials obtained by non-electrochemical methods. Additional advantages of electrochemically obtained composites are the lower content of noble metal, the uniform distribution of the charge over an extended potential range, and, importantly, the simplicity of the preparation method. It was also found that when deposited on a Co3O4 substrate, Pt particles show, besides an enhanced active surface area, an improved catalytic activity for methanol anodic oxidation. This behavior was tentatively ascribed to the presence of a high amount of platinum-oxidized species.

Ageing of nickel used as sensitive material for early detection of sudomotor dysfunction

The surface ageing of nickel electrodes was studied in the frame of the development of non-invasive biomedical devices, dedicated to the detection of sudomotor dysfunction manifested by an alteration of the ionic balance in human sweat. In this kind of technology, low voltage potentials with variable amplitudes are applied to nickel electrodes, placed on skin regions with a high density of sweat glands, and the electrical responses are measured. The trick is that nickel electrodes play alternately the role of anode and cathode, thus the analysis of the temporal evolution of the physico-chemical properties of nickel is of prime importance to ensure the good performance of the device. Electrochemical measurements coupled to surface chemical characterizations (X-ray photoelectron spectroscopy (XPS), Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS)) were performed on pure Ni samples, immersed in buffered chloride solutions mimicking human sweat. The shapes of voltammograms, recorded in a restricted anodic potential range, show that the nickel surface was gradually passivated as a function of the number of scans. This was confirmed by XPS data, with the formation of a 1nm thick duplex layer composed by nickel hydroxide (outermost layer) and nickel oxide (inner layer). In a negative extended potential range, though the electrochemical behavior of electrodes was not modified upon cycling the potential, XPS data show that the inner layer was thickening, indicating a surface degradation of the nickel electrode. Below pitting potentials, adsorbed chloride was only hardly detected by XPS, and the surface composition of the nickel samples was similar after treatments in chloride or chloride-free buffered solutions. In a larger potential range enabling to reach the breakdown potential, the highly chemically sensitive ToF-SIMS characterization pointed out that the surface concentration of adsorbed chloride was higher in pits than elsewhere on the surface sample.

Performance Improvement by Tungsten Oxides of the Pt-RuOxHy Electrocatalyst for Methanol Oxidation

Abstract The dissolution of hydrous ruthenium oxide (RuOxHy) from a Pt-RuOxHy anode catalyst supported on multi-walled carbon nanotubes (MWCNTs) during pretreatment over an extended potential range (−0.20–0.96 V vs SCE) can be dramatically reduced from 70% to 15% by the addition of WOm. The Pt-RuOxHy-WOm catalyst did not lose activity according to chronoamperometric measurement of methanol oxidation after an extended potential range pretreatment compared with that pretreated in a narrow potential range (−0.20–0.46 V vs SCE) where no ruthenium dissolution occurred. In contrast, the activity loss of the reference Pt-RuOxHy catalyst was as high as 50%.

Electrochemistry Using Self-Assembled DNA Monolayers on Highly Oriented Pyrolytic Graphite

Duplex DNA functionalized with pyrene has been utilized to fabricate DNA-modified electrodes on highly oriented pyrolytic graphite (HOPG). Films have been characterized using AFM and radioactive labeling as well as electrochemically. The data obtained are consistent with a close-packed structure in the film with helices oriented in a nearly upright orientation, as seen earlier with the fabrication of thiol-tethered duplexes on gold. Also as on gold, we observe the reduction of DNA-bound intercalators in a DNA-mediated reaction. The reduction of the intercalator is attenuated in the presence of the single-base mismatches, CA and GT, independent of the sequence composition of the oligonucleotide. This sensitivity to single-base mismatches is enhanced when methylene blue reduction is coupled in an electrocatalytic cycle with ferricyanide. The extended potential range afforded by the HOPG surface has allowed us also to investigate the electrochemistry of previously inaccessible metallointercalators, Ru(bpy)2dppz2+ and Os(phen)2dppz2+, at the DNA-modified HOPG surface. These results support the application of DNA-modified HOPG as a convenient and reproducible surface for electrochemical DNA sensors using DNA-mediated charge transport.

Electrochemomechanical deformation studies of [Fe(CN) 6] 3− ion doped conducting polypyrrole film

Electrochemomechanical deformation (ECMD) studies have been performed in the electrochemically prepared freestanding film of ferricyanide ion doped polypyrrole (PPy). The ECMD studies conducted on these polymer films show an increasing order of deformation in accordance with the extent of solvation of the alkali metal cation (K +<Na +<Li +) of supporting electrolyte in aqueous medium. The excess charge on Fe(CN) 6 3−/4− in addition to negative charge generated over the PPy film during the electrochemical reduction was compensated by inserting supporting electrolyte cation, at an extended potential range of −0.85 to +0.7 V vs. Ag/AgCl. The appearance of an appreciable magnitude of deformation in the PPy film in a smaller potential window of −0.25 to +0.6 V indicates a significant contribution of Fe(CN) 6 3−/4− dopant towards the total deformation of the polymer film.

UV-visible and IR spectroelectrochemical properties of V2O5 crystalline films charged/discharged in extended potential range

Electrochemical properties of amorphous and crystalline V2O5 films, dip-coated from V-oxoisopropoxide sols and thermally treated at various temperatures (100, 150, 200 and 300°C), have been studied in extended potential range, i.e. from 1.4 to −1.6 V vs. Ag/AgCl in 1M LiClO4/propylen carbonate (PC) electrolyte. The formation of various lithiated (α-, δ-, e- and γ-LixV2O5) phases was correlated with the values of insertion coefficient x obtained from cyclic voltammograms (CV) of crystalline V2O5 films (300°C). Reversible charging was observed when films were cycled up to −1.0 V vs. Ag/AgCl, while the extension of the potential to −1.3 V vs. Ag/AgCl change the CV of films irreversibly. Charging of crystalline V2O5 films was followed by the help of in-situ UV-visible spectroscopy, that revealed the intensity variations of the polaron absorption above 600 nm and the presence of the absorbing V3+ species between 550 and 650 nm. Ex-situ IR spectra of the crystalline films charged/discharged at −1.6V/1.4V vs. Ag/AgCl confirmed the amorphisation of the films' structure.

Electrochemistry of LiMnO 2 over an extended potential range

A kinetic study of potential versus composition was conducted on orthorhombic LiMnO 2 over the voltage range of 1.0 to 4.6 V with a variety of electrolyte formulations. The broad potential range enabled studying the electrochemical behaviour of the material over compositions from LiMnO 2 to Li 0.1MnO 2. Substantial differences in the kinetics of the electrochemical processes associated with certain potential ranges were observed.

On the simultaneous evaluation of charge transfer kinetics and adsorption: reduction of parabanic acid in low acidity xM HCl + (2 − x)M LiCl mixtures

Parabanic acid reduction has been studied in low acidity xM HCl + (2 − x)M LiCl mixtures by the faradaic impedance method. The overall reaction obeys an electrochemical scheme with a quasi-reversible electron transfer, a coupled homogeneous following reaction and weakly adsorbed reactant and products; the reaction is further complicated by the presence of a polarographic maximum. Analysis of the electrode admittance over an extended potential range (about 1 V) allowed the determination of the electron transfer and adsorption parameters.