Determination of Adsorption Isotherms of Overpotentially Deposited Hydrogen on Platinum and Iridium in KOH Aqueous Solution Using the Phase-Shift Method and Correlation Constants

The phase-shift method and correlation constants, that is, unique electrochemical impedance spectroscopy (EIS) techniques for studying the linear relationship between the behavior (−φ vs E) of the phase shift (90° ≥ −φ ≥ 0°) for the optimum intermediate frequency and that (θ vs E) of the fractional surface coverage (0 ≤ θ ≤ 1), are proposed and verified to determine the Frumkin, Langmuir, and Temkin adsorption isotherms of overpotentially deposited hydrogen (OPD H) and related electrode kinetic and thermodynamic parameters of noble metals (alloys) in aqueous solutions. On Pt and Ir in 0.1 M KOH aqueous solution, the Frumkin and Temkin adsorption isotherms (θ vs E), equilibrium constants (K), interaction parameters (g), rates (r) of change of the standard free energy of OPD H with θ, and standard free energies (ΔGθ0) of OPD H are determined using the phase-shift method and correlation constants. The Frumkin adsorption isotherm is more accurate, useful, and effective than the Temkin adsorption isotherm. At 0.2 < θ < 0.8, the negative (positive) values of the interaction parameter for the Frumkin (Temkin) adsorption isotherms of OPD H are determined. A lateral attraction or repulsion interaction between the adsorbed OPD H species appears. The duality of the lateral attraction and repulsion interactions is probably a unique feature of OPD H on Pt, Ir, and Pt−Ir alloys in aqueous solutions

Determination of Adsorption Isotherms of Hydroxide and Deuteroxide on Pt−Ir Alloy in LiOH Solutions Using the Phase-Shift Method and Correlation Constants

The phase-shift method and correlation constants, that is, unique electrochemical impedance spectroscopy techniques for studying the linear relationship between the behavior (−φ vs E) of the phase shift (90° ≥ −φ ≥ 0°) for the optimum intermediate frequency and that (θ vs E) of the fractional surface coverage (0 ≤ θ ≤ 1) of intermediates for sequential reactions, are proposed and verified to determine the Frumkin, Langmuir, and Temkin adsorption isotherms and related electrode kinetic and thermodynamic parameters. On Pt−Ir (90:10 % (by weight)) alloy in 0.1 M LiOH (H2O) and 0.1 M LiOH (D2O) solutions, the Frumkin and Temkin adsorption isotherms (θ vs E), equilibrium constants (K), interaction parameters (g), rates (r) of change of the standard Gibbs energies of hydroxide (OH) and hydroxide and deuteroxide (OH, OD) with θ, and standard Gibbs energies (ΔGθ0) of OH and (OH, OD) are determined and compared using the phase-shift method and correlation constants. Depending on θ (0 ≤ θ ≤ 1), the value of K for OH is approximately 1.4 to 11.5 times greater than that for (OH, OD). The OD effect on the adsorption of (OH, OD) on the Pt−Ir alloy in 0.1 M LiOH (D2O) solution is not negligible, especially when E is high and θ ≈ 1. Both the values of K for OH and (OH, OD) decrease with increasing E and θ. A lateral repulsion (g > 0) interaction between the adsorbed OH or (OH, OD) species appears

Determination of the Adsorption Isotherms of Hydrogen and Deuterium Isotopes on a Pt−Ir Alloy in LiOH Solutions Using the Phase-Shift Method and Correlation Constants

The phase-shift method and correlation constants, which are unique electrochemical impedance spectroscopy techniques for studying the linear relationship between the phase shift (90° ≥ −φ ≥ 0°) versus electric potential (E) behavior for the optimum intermediate frequency and the fractional surface coverage (0 ≤ θ ≤ 1) vs E behavior, are proposed and verified to determine the Frumkin, Langmuir, and Temkin adsorption isotherms and related electrode kinetic and thermodynamic parameters. On a Pt−Ir alloy (90:10 mass ratio) in 0.1 M LiOH (H2O) and 0.1 M LiOH (D2O) solutions, the Frumkin and Temkin adsorption isotherms (θ vs E), equilibrium constants (K), interaction parameters (g), standard Gibbs energies (ΔGθ°) of hydrogen (H) and deuterium (D) adsorption, and rates of change (r) of ΔGθ° of H and D with θ have been determined and are compared using the phase-shift method and correlation constants. The value of K decreases in going from H2O to D2O. The values of K for both H and D increase with increasing E and θ. Over the θ range (i.e., 1 ≥ θ ≥ 0), the value of K for H is 3.7 to 4.1 times greater than that for D. For 0.2 g g > 0) interaction between the adsorbed H or D species appears. The duality of the lateral attractive and repulsive interactions is a unique feature of the adsorbed H and D species on Pt, Ir, and Pt−Ir alloys in acidic and alkaline H2O and D2O solutions

Determination of the Adsorption Isotherms of Overpotentially Deposited Hydrogen on a Pt−Ir Alloy in H₂SO₄ Aqueous Solution Using the Phase-Shift Method and Correlation Constants

The phase-shift method and correlation constants, which are unique electrochemical impedance spectroscopy techniques for studying the linear relationship between the phase shift (90° ≥ −φ ≥ 0°) versus electric potential (E) behavior for the optimum intermediate frequency and the fractional surface coverage (0 ≤ θ ≤ 1) vs E behavior, are proposed and verified to determine the Frumkin, Langmuir, and Temkin adsorption isotherms and related electrode kinetic and thermodynamic parameters. On a Pt−Ir [90:10 % (by weight)] alloy in 0.5 M H2SO4 aqueous solution, the Frumkin and Temkin adsorption isotherms (θ vs E), equilibrium constants [K = 3.3 · 10−5 exp(2.5θ) mol−1 for the Frumkin and K = 3.3 · 10−4 exp(−2.1θ) mol−1 for the Temkin adsorption isotherm], interaction parameters (g = −2.5 for the Frumkin and g = 2.1 for the Temkin adsorption isotherm), standard Gibbs energies of adsorption of overpotentially deposited (OPD) H [(25.6 ≥ ΔGθ0 ≥ 19.4) kJ·mol−1 for K = 3.3 · 10−5 exp(2.5θ) mol−1 and 0 ≤ θ ≤ 1 and (20.9 Gθ0 −1 for K = 3.3 · 10−4 exp(−2.1θ) mol−1 and 0.2 Gθ0 of OPD H with θ (r = −6.2 kJ·mol−1 for g = −2.5 and r = 5.2 kJ·mol−1 for g = 2.1) have been determined and are compared using the phase-shift method and correlation constants. For 0.2 g g > 0) interaction between the adsorbed OPD H species appears. On Pt, Ir, and Pt−Ir alloys in 0.5 M H2SO4 aqueous solution, the values of K for the Frumkin adsorption isotherms of OPD H decrease with increasing mass ratio of Ir. Negative values of g for the Frumkin adsorption isotherms of OPD H on the Pt, Ir, and Pt−Ir alloys in acidic and alkaline H2O and D2O solutions are experimentally and consistently determined. The duality of the lateral attractive and repulsive interactions is a unique feature of the adsorbed OPD H species on the Pt, Ir, and Pt−Ir alloys in acidic and alkaline H2O and D2O solutions

Facile Preparation of Magnetite-Incorporated Polyacrylonitrile-Derived Carbons for Li-Ion Battery Anodes

A facile preparation method for magnetite (Fe3O4)-incorporated polyacrylonitrile (PAN)-derived carbon composites was developed to overcome the limitations of graphite-based materials for Li-ion batteries (LIBs), and the electrochemical performance of this material as an anode for LIBs was investigated. In this study, Fe3O4 nanoparticles (NPs) with hydrophobic surfaces and graphitizable hydrophobic PAN formed through radical polymerization were uniformly distributed in an emulsion system, and subsequently, a partially graphitic carbon composite containing Fe3O4 NPs was obtained through simple oxidation and carbonization processes. The presence of Fe3O4 NPs contributed to a slight increase in the graphitization efficiency of PAN, as well as the additional uptake of lithium ions in LIBs. As a result, when the developed composite was applied as an anode for LIBs, they exhibited increased specific capacities and stable cycle performance over more than 100 cycles. In particular, it was confirmed that the rate capability of the composite was significantly higher than that of commercial graphite. The results indicate that the developed composite is promising for applications in advanced LIBs that are specialized for high-power devices

Block Copolymer Directed Ordered Mesostructured TiNb₂O₇ Multimetallic Oxide Constructed of Nanocrystals as High Power Li-Ion Battery Anodes

In order to achieve high-power and -energy anodes operating above 1.0 V (vs Li/Li⁺), titanium-based materials have been investigated for a long time. However, theoretically low lithium charge capacities of titanium-anodes have required new types of high-capacity anode materials. As a candidate, TiNb₂O₇ has attracted much attention due to the high theoretical capacity of 387.6 mA h g^–1. However, the high formation temperature of the TiNb₂O₇ phase resulted in large-sized TiNb₂O₇ crystals, thus resulting in poor rate capability. Herein, ordered mesoporous TiNb₂O₇ (denoted as m-TNO) was synthesized by block copolymer assisted self-assembly, and the resulting binary metal oxide was applied as an anode in a lithium ion battery. The nanocrystals (∼15 nm) developed inside the confined pore walls and large pores (∼40 nm) of m-TNO resulted in a short diffusion length for lithium ions/electrons and fast penetration of electrolyte. As a stable anode, the m-TNO electrode exhibited a high capacity of 289 mA h g^–1 (at 0.1 C) and an excellent rate performance of 162 mA h g^–1 at 20 C and 116 mA h g^–1 at 50 C (= 19.35 A g^–1) within a potential range of 1.0–3.0 V (vs Li/Li⁺), which clearly surpasses other Ti-and Nb-based anode materials (TiO₂, Li₄Ti₅O₁₂, Nb₂O₅, etc.) and previously reported TiNb₂O₇ materials. The m-TNO and carbon coated m-TNO electrodes also demonstrated stable cycle performances of 48 and 81% retention during 2,000 cycles at 10 C rate, respectively

Scalable Dry Process for Fabricating a Na Superionic Conductor-Type Solid Electrolyte Sheet

The cost reduction and mass production of oxide-based solid electrolytes are critical for the commercialization of all-solid-state batteries. In this study, an environmentally friendly, low-cost, and high-density oxide-based Na superionic conductor-type solid electrolyte sheet was fabricated via a dry process without the use of any solvent. The polytetrafluoroethylene (PTFE), used as a binder, was transformed into thin thread-like structures via shear force, resulting in a flexible solid electrolyte sheet. The solid electrolyte powder quantity was limited to 50 wt % for fabricating a uniform green sheet via the wet process. However, when the dry process was employed for green sheet fabrication, the solid electrolyte powder quantity could be increased to values exceeding 95 wt %. Therefore, the green sheets produced by using the dry process demonstrated a higher density than those fabricated by using the wet process. The binder content and particle size affected the ionic conductivity of a solid electrolyte sheet fabricated via a dry process. The sheet obtained via the blending of 3 wt % PTFE binder with a solid electrolyte powder, finely ground using a planetary ball mill, which exhibited the highest total ionic conductivity of 1.03 mS cm–1

Alkali Extraction to Detoxify Rice Husk-Derived Silica and Increase Its Biocompatibility

As interest in natural biogenic silica nanoparticles (NPs) from rice husks grows, it is important to know how their preparation (i.e., combustion, acid leaching, or alkali extraction) impacts their biocompatibility. Acid leaching and alkali extraction both generated highly pure silica NPs (>99.1% SiO2 vs 93.1% with combustion). However, toxicity tests with six different human and mouse cell lines found alkali-extracted silica NPs were the least harmful; for example, the concentration leading to 50% loss in viability (LC50) was typically around 500, 500–2000, and >2000 mg/L for the combustion, acid-leached, and alkali-extracted silica NPs, respectively. To mimic the presence of carbon during calcination (900 °C for 6 h), polyethylene glycol (PEG) was incorporated in the alkali-extracted silica NPs prior to this step. This significantly increased their toxicities; that is, the LC50 dropped to between 500 and 2000 mg/L and was exacerbated further when calcination was performed at a lower temperature and time (550 °C for 2 h): LC50 values dropped to between 62.5 to 1000 mg/L. These results show that the biocompatibility of rice husk-derived silica NPs is negatively affected by the presence of residual carbon during calcination, but also that it can be significantly improved via alkali extraction

Mesoporous Ge/GeO₂/Carbon Lithium-Ion Battery Anodes with High Capacity and High Reversibility

We report mesoporous composite materials (m-GeO₂, m-GeO₂/C, and m-Ge-GeO₂/C) with large pore size which are synthesized by a simple block copolymer directed self-assembly. m-Ge/GeO₂/C shows greatly enhanced Coulombic efficiency, high reversible capacity (1631 mA h g^–1), and stable cycle life compared with the other mesoporous and bulk GeO₂ electrodes. m-Ge/GeO₂/C exhibits one of the highest areal capacities (1.65 mA h cm^–2) among previously reported Ge- and GeO₂-based anodes. The superior electrochemical performance in m-Ge/GeO₂/C arises from the highly improved kinetics of conversion reaction due to the synergistic effects of the mesoporous structures and the conductive carbon and metallic Ge

Direct O–O Coupling Promoted the Oxygen Evolution Reaction by Dual Active Sites from Ag/LaNiO₃ Interfaces

The development of highly active oxygen evolution reaction (OER) electrocatalysts is one of the most important issues for advanced water electrolysis technology with high energy efficiency. However, according to the conventional adsorbate evolution mechanism (AEM), the OER activity is theoretically limited with high overpotential by the scaling relationship in binding energies of the reaction intermediates. We propose an attractive strategy to promote OER activity by direct O–O coupling at the interfacial active sites for Ag (x) nanoparticles decorated on La1–xNiO3 perovskite electrocatalysts (Ag/LNO-x). The overpotential of the Ag/LNO-0.05 was 315 mV at a current density of 10 mA cm–2geo, which was much lower than that of other Ag/LNO-x (x = 0, 0.3, and 0.5) and commercial iridium oxide (IrO2, 398 mV) electrocatalysts. The theoretical calculation revealed that the improved OER electrocatalytic activity of Ag/LNO-x originated from a change in the reaction mechanism at the interfacial active sites. At the interface, oxygen evolution via the dual-site mechanism with direct O–O coupling becomes more favorable than that via the conventional AEM. Finally, due to the formation of the interfacial active sites, the synthesized Ag/LNO-0.05 electrocatalyst showed significantly enhanced OER activity, which was 20 times higher mass activity before and 74 times after an accelerated durability test than that of the IrO2 electrocatalyst