CO Oxidation on Planar Au/TiO2_{2} Model Catalysts under Realistic Conditions: A Combined Kinetic and IR Study

The oxidation of CO on planar Au/TiO$_{2}$ model catalysts was investigated under pressure and temperature conditions similar to those for experiments with more realistic Au/TiO$_{2}$ powder catalysts. The effects of a change of temperature, pressure, and gold coverage on the CO oxidation activity were studied. Additionally, the reasons for the deactivation of the catalysts were examined in long‐term experiments. From kinetic measurements, the activation energy and the reaction order for the CO oxidation reaction were derived and a close correspondence with results of powder catalysts was found, although the overall turnover frequency (TOF) measured in our experiments was around one order of magnitude lower compared to results of powder catalysts under similar conditions. Furthermore, long‐term experiments at 80 °C showed a decrease of the activity of the model catalysts after some hours. Simultaneous in‐situ IR experiments revealed a decrease of the signal intensity of the CO vibration band, while the tendency for the build‐up of side products (e. g. carbonates, carboxylates) of the CO oxidation reaction on the surface of the planar model catalysts was rather low

Modified Solid Electrolyte Interphases with Alkali Chloride Additives for Aluminum–Sulfur Batteries with Enhanced Cyclability

Aluminum–sulfur batteries employing high-capacity and low-cost electrode materials, as well as non-flammable electrolytes, are promising energy storage devices. However, the fast capacity fading due to the shuttle effect of polysulfides limits their further application. Herein, alkaline chlorides, for example, LiCl, NaCl, and KCl are proposed as electrolyte additives for promoting the cyclability of aluminum–sulfur batteries. Using NaCl as a model additive, it is demonstrated that its addition leads to the formation of a thicker, Na$_x$Al$_y$O$_2$-containing solid electrolyte interphase on the aluminum metal anode (AMA) reducing the deposition of polysulfides. As a result, a specific discharge capacity of 473 mAh g$^{−1}$ is delivered in an aluminum–sulfur battery with NaCl-containing electrolyte after 50 dis-/charge cycles at 100 mA g$^{−1}$. In contrast, the additive-free electrolyte only leads to a specific capacity of 313 mAh g$^{−1}$ after 50 cycles under the same conditions. A similar result is also observed with LiCl and KCl additives. When a KCl-containing electrolyte is employed, the capacity increases to 496 mA h g$^{−1}$ can be achieved after 100 cycles at 50 mA g$^{−1}$. The proposed additive strategy and the insight into the solid electrolyte interphase are beneficial for the further development of long-life aluminum–sulfur batteries

High Active Material Loading in Organic Electrodes Enabled by an in‐situ Electropolymerized π‐Conjugated Tetrakis (4‐Aminophenyl) Porphyrin

Porphyrin complexes have been widely studied as promising electrode material in diverse energy storage systems and chemistries. However, like other organic electrodes, porphyrins often suffer from low conductivity and, consequently, require a significant amount (typically 40 %) of electrochemically inactive conductive carbon that occupies volume and mass without storing energy. In this study, we investigate [5,10,15,20 tetrakis(4-aminophenyl)-porphyrin] (TAPP) and its metal complexes as redox-active cathode materials to address the aforementioned issues. The lithium-ion cells prepared with a high content of CuTAPP active material (70 wt %) demonstrate a stable discharge capacity of ∼120 mAh/g when cycling with a constant current density of 1000 mA/g. The material also showed superior rate capability, e. g., ∼60 mAh/g at 8 A/g. The results of DFT calculations and experimental analysis indicate that the degree of planarity of the metalloporphyrins directly correlates to their cycling stability. Moreover, the contribution from the central metal redox during the cycling is found to be the reason for the significantly higher performance of the Cu-complex compared to the metal-free complex. The findings of this study show a general approach for facing common conductivity challenges of organic electrodes and open up a pathway for practical application of organics electrode materials in energy storage application

A beneficial combination of formic acid as a processing additive and fluoroethylene carbonate as an electrolyte additive for Li4_{4}Ti5_{5}O12_{12} lithium-ion anodes

The aqueous processing of lithium transition metal oxide active materials such as Li$_{4}$Ti$_{5}$O$_{12}$ (LTO) into electrodes remains a challenge owing to the high reactivity of such materials in contact with water, resulting in a rapid pH increase, aluminum current collector corrosion, and inferior cycling stability. Herein, the addition of formic acid (FA) as an electrode slurry processing additive is investigated, including a variation of the mixing speed as an additional important parameter. Following the identification of suitable electrode preparation conditions, the effect of fluoroethylene carbonate (FEC) as an electrolyte additive is studied in half-cells and full-cells comprising a LiNi$_{0.5}$Mn$_{0.3}$Co$_{0.2}$O$_{2}$ (NMC$_{532}$) based positive electrode. Owing to the beneficial impact of FEC on the solid electrolyte interphase (SEI) formed at the LTO|electrolyte interface, involving specifically the suppression of lithium salt decomposition, both the half-cells and the LTO‖NMC$_{532}$ full-cells exhibit a superior performance, achieving a capacity retention of 84.3% and 64.1% after 5000 and 10 000 cycles at 2C, respectively

Layered Oxide Material as a Highly Stable Na‐ion Source and Sink for Investigation of Sodium‐ion Battery Materials

Investigating Na-ion battery (SIB) materials is complicated by the absence of a well-performing (reference) electrode material since sodium metal cannot be considered as a quasi-reference electrode. Taking advantage of the activity of both Ni and Mn, herein, the P2-type and Mn-rich Na$_{0.6}$Ni$_{0.22}$Al$_{0.11}$Mn$_{0.66}$O$_2$ (NAM) material, known to be an excellent positive electrode, is investigated as a negative electrode. To prove NAM stability as both positive and negative electrode, symmetric cells have been assembled without pre-sodiation, which showed a reversible capacity of 73 mA h g$^{−1}$ and a remarkable capacity retention of 82.6 % after 500 cycles. The outstanding cycling performance is ascribed to the high stability of the active material at both the highest and lowest Na-ion storage plateaus and the rather limited electrolyte decomposition and solid-electrolyte-interphase (SEI) formation occurring. The long-term stability of NAM at both electrodes enables its use as a “reference” electrode for the investigation of other positive and negative electrode materials for SIBs, resembling the role played by lithium titanate (LTO) and lithium iron phosphate (LFP) in LIBs

Solvent-Dictated Sodium Sulfur Redox Reactions: Investigation of Carbonate and Ether Electrolytes

Sulfur-based cathode chemistries are essential for the development of high energy density alkali-ion batteries. Here, we elucidate the redox kinetics of sulfur confined on carbon nanotubes, comparing its performance in ether-based and carbonate-based electrolytes at room temperature. The solvent is found to play a key role for the electrochemical reactivity of the sulfur cathode in sodium–sulfur (Na–S) batteries. Ether-based electrolytes contribute to a more complete reduction of sulfur and enable a higher electrochemical reversibility. On the other hand, an irreversible solution-phase reaction is observed in carbonate solvents. This study clearly reveals the solvent-dependent Na–S reaction pathways in room temperature Na–S batteries and provides an insight into realizing their high energy potential, via electrolyte formulation design

Metal–Organic Framework Derived Fe7_{7}S8_{8} Nanoparticles Embedded in Heteroatom-Doped Carbon with Lithium and Sodium Storage Capability

Iron sulfides are promising materials for lithium- and sodium-ion batteries owing to their high theoretical capacity and widespread abundance. Herein, the performance of an iron sulfide-carbon composite, synthesized from a Fe-based metal–organic framework (Fe-MIL-88NH2) is reported. The material is composed of ultrafine Fe7S8 nanoparticles (<10 nm in diameter) embedded in a heteroatom (N, S, and O)-doped carbonaceous framework (Fe7S8@HD-C), and is obtained via a simple and efficient one-step sulfidation process. The Fe7S8@HD-C composite, investigated in diethylene glycol dimethyl ether-based electrolytes as anode material for lithium and sodium batteries, shows high reversible capacities (930 mAh g−1 for lithium and 675 mAh g−1 for sodium at 0.1 A g−1). In situ X-ray diffraction reveals an insertion reaction to occur in the first lithiation and sodiation steps, followed by conversion reactions. The composite electrodes show rather promising long-term cycling stability and rate capability for sodium storage in glyme electrolyte, while an improved rate capacity and long-term cycling stability (800 mAh g−1 after 300 cycles at 1 A g−1) for lithium can be achieved using conventional carbonates

Establishing a Stable Anode–Electrolyte Interface in Mg Batteries by Electrolyte Additive

Simple magnesium salts with high electrochemical and chemical stability and adequate ionic conductivity represent a new-generation electrolyte for magnesium (Mg) batteries. Similar to other Mg electrolytes, the simple-salt electrolyte also suffers from high charge-transfer resistance on the Mg surface due to the adsorbed species in the solution. In the current study, we built a model Mg cell system with the Mg[B(hfip)4]2/DME electrolyte and Chevrel phase Mo6S8 cathode, to demonstrate the effect of such anode–electrolyte interfacial properties on the full-cell performance. It was found that the cell required additional activation cycles to achieve its maximal capacity. The activation process is mainly attributed to the conditioning of the anode–electrolyte interface, which could be boosted by introducing an additive amount of Mg(BH4)2 to the Mg[B(hfip)4]2/DME electrolyte. Electrochemical and spectroscopic analyses revealed that the Mg(BH4)2 additive helps to remove the native oxide layer and promotes the formation of a solid electrolyte interphase layer on Mg. As a result, the full cell with the additive-containing electrolyte delivered a stable capacity from the second cycle onward. Further battery tests showed a reversible cycling for 600 cycles and an excellent rate capability, indicating good compatibility of the Mg(BH4)2 additive. The current study not only provides fundamental insights into the interfacial phenomena in Mg batteries but also highlights the facile tunability of the simple-salt Mg electrolytes

Reinforcing the Electrode/Electrolyte Interphases of Lithium Metal Batteries Employing Locally Concentrated Ionic Liquid Electrolytes

Lithium metal batteries (LMBs) with nickel-rich cathodes are promising candidates for next-generation high-energy-density batteries, but the lack of sufficiently protective electrode/electrolyte interphases (EEIs) limits their cyclability. Herein, trifluoromethoxybenzene is proposed as a cosolvent for locally concentrated ionic liquid electrolytes (LCILEs) to reinforce the EEIs. With a comparative study of a neat ionic liquid electrolyte (ILE) and three LCILEs employing fluorobenzene, trifluoromethylbenzene, or trifluoromethoxybenzene as cosolvents, it is revealed that the fluorinated groups tethered to the benzene ring of the cosolvents not only affect the electrolytes’ ionic conductivity and fluidity, but also the EEIs’ composition via adjusting the contribution of the 1-ethyl-3-methylimidazolium cation (Emim$^+$) and bis(fluorosulfonyl)imide anion. Trifluoromethoxybenzene, as the optimal cosolvent, leads to a stable cycling of LMBs employing 5 mAh cm$^{−2}$ lithium metal anodes (LMAs), 21 mg cm$^{−2}$ LiNi$_{0.8}$Co$_{0.15}$Al$_{0.05}$ (NCA) cathodes, and 4.2 µL mAh$^{−1}$ electrolytes for 150 cycles with a remarkable capacity retention of 71%, thanks to a solid electrolyte interphase rich in inorganic species on LMAs and, particularly, a uniform cathode/electrolyte interphase rich in Emim$^+$-derived species on NCA cathodes. By contrast, the capacity retention under the same condition is only 16%, 46%, and 18% for the neat ILE and the LCILEs based on fluorobenzene and benzotrifluoride, respectively