Automation in und mit der Analytischen Chemie

Ohne Zusammenfassung

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Automation in and with analytical chemistryV. Classification of working ranges in analytical chemistry with regard to computers

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Teil IV: diese Z. 256, 7 (1971)     

Stable Potential Windows for Long‐Term Electrocatalysis by Manganese Oxides Under Acidic Conditions

Efficient, earth‐abundant, and acid‐stable catalysts for the oxygen evolution reaction (OER) are missing pieces for the production of hydrogen via water electrolysis. Here, we report how the limitations on the stability of 3d‐metal materials can be overcome by the spectroscopic identification of stable potential windows in which the OER can be catalyzed efficiently while simultaneously suppressing deactivation pathways. We demonstrate the benefits of this approach using gamma manganese oxide (γ‐MnO₂), which shows no signs of deactivation even after 8000 h of electrolysis at a pH of 2. This stability is vastly superior to existing acid‐stable 3d‐metal OER catalysts, but cannot be realized if there is a deviation as small as 50‐mV from the stable potential window. A stable voltage efficiency of over 70 % in a polymer–electrolyte membrane (PEM) electrolyzer further verifies the availability of this approach and showcases how materials previously perceived to be unstable may have potential application for water electrolysis in an acidic environment.     

Organic Proton‐Buffer Electrode to Separate Hydrogen and Oxygen Evolution in Acid Water Electrolysis

Hydrogen production from water via electrolysis in acid is attracting extensive attention as an attractive alternative approach to replacing fossil fuels. However, the simultaneous evolution of H₂ and O₂ requires a fluorine‐containing proton exchange membrane to prevent the gases from mixing while using the same space to concentrate the gases, which significantly increases the cost and reduces the flexibility of this approach. Here, a battery electrode based on the highly reversible enolization reaction of pyrene‐4,5,9,10‐tetraone is first introduced as a solid‐state proton buffer to separate the O₂ and H₂ evolution of acidic water electrolysis in space and time, through which the gas mixing issue can be avoided without using any membrane. This process allows us to separately consider H₂ and O₂ production according to the variation in input power (e.g., the renewable energy) and/or the location for H₂ concentration, thus showing high flexibility for H₂ production.     

A Sustainable Solid Electrolyte Interphase for High-Energy-Density Lithium Metal Batteries Under Practical Conditions

High-energy-density Li metal batteries suffer from a short lifespan under practical conditions, such as limited lithium, high loading cathode, and lean electrolytes, owing to the absence of appropriate solid electrolyte interphase (SEI). Herein, a sustainable SEI was designed rationally by combining fluorinated co-solvents with sustained-release additives for practical challenges. The intrinsic uniformity of SEI and the constant supplements of building blocks of SEI jointly afford to sustainable SEI. Specific spatial distributions and abundant heterogeneous grain boundaries of LiF, LiN_xO_y, and Li₂O effectively regulate uniformity of Li deposition. In a Li metal battery with an ultrathin Li anode (33 μm), a high-loading LiNi_0.5Co_0.2Mn_0.3O₂ cathode (4.4 mAh cm⁻²), and lean electrolytes (6.1 g Ah⁻¹), 83 % of initial capacity retains after 150 cycles. A pouch cell (3.5 Ah) demonstrated a specific energy of 340 Wh kg⁻¹ for 60 cycles with lean electrolytes (2.3 g Ah⁻¹).     

Iridium‐Based Cubic Nanocages with 1.1‐nm‐Thick Walls: A Highly Efficient and Durable Electrocatalyst for Water Oxidation in an Acidic Medium

We report a highly active and durable water oxidation electrocatalyst based on cubic nanocages with a composition of Ir₄₄Pd₁₀, together with well‐defined {100} facets and porous walls of roughly 1.1 nm in thickness. Such nanocages substantially outperform all the water oxidation electrocatalysts reported in literature, with an overpotential of only 226 mV for reaching 10 mA cm^?2_geo at a loading of Ir as low as 12.5 μg_Ir cm^?2 on the electrode in acidic media. When benchmarked against a commercial Ir/C electrocatalyst at 250 mV of overpotential, such a nanocage‐based catalyst not only shows enhancements (18.1‐ and 26.2‐fold, respectively) in terms of mass (1.99 A mg^?1_Ir) and specific (3.93 mA cm^?2_Ir) activities, but also greatly enhanced durability. The enhancements can be attributed to a combination of multiple merits, including a high utilization efficiency of Ir atoms and an open structure beneficial to the electrochemical oxidation of Ir to the active form of IrO_x.     

Graphite Anode for a Potassium‐Ion Battery with Unprecedented Performance

Graphite as an anode for the potassium ion battery (PIBs) has the merits of low cost and potentially high energy density, while suffering from limited cycle time and inferior stability. Herein we, using a concentrated electrolyte, demonstrate that formation of a robust inorganic‐rich passivation layer on the graphite anode could resolve these problems. Consequently, the PIBs with graphite anode could operate for over 2000 cycles (running time of over 17 months) with negligible capacity decay, and had a high area capacity over 7.36 mAh cm^?2 with a high mass loading of 28.56 mg cm^?2. These unprecedented performances of graphite are comparable to that of traditional lithium‐ion batteries, and may promote the rapidly development of high performance PIBs.     

A Membrane‐Free Redox Flow Battery with Two Immiscible Redox Electrolytes

Flexible and scalable energy storage solutions are necessary for mitigating fluctuations of renewable energy sources. The main advantage of redox flow batteries is their ability to decouple power and energy. However, they present some limitations including poor performance, short‐lifetimes, and expensive ion‐selective membranes as well as high price, toxicity, and scarcity of vanadium compounds. We report a membrane‐free battery that relies on the immiscibility of redox electrolytes and where vanadium is replaced by organic molecules. We show that the biphasic system formed by one acidic solution and one ionic liquid, both containing quinoyl species, behaves as a reversible battery without any membrane. This proof‐of‐concept of a membrane‐free battery has an open circuit voltage of 1.4 V with a high theoretical energy density of 22.5 Wh L⁻¹, and is able to deliver 90 % of its theoretical capacity while showing excellent long‐term performance (coulombic efficiency of 100 % and energy efficiency of 70 %).