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

Bulk and Surface Stabilization Process of Metastable Li-Rich Disordered Rocksalt Oxyfluorides as Efficient Cathode Materials

Manganese based disordered rocksalt systems have attracted attention as Co-free and high capacity cathode materials for Li-ion batteries. However, for a practical application these materials are considered as metastable and exhibit too limited cyclability. In order to improve the structural stability of the disordered rocksalt Li$_{1+x}$Mn$_{2/3}$Ti$_{1/3}$O$_2$F$_x$ (0 ≤ x ≤ 1) system during cycling, we have introduced a mild temperature heat treatment process under reducing atmosphere, which is intended to overcome the structural anomalies formed during the mechanochemical synthesis. The heat-treated samples presented better electrochemical properties, which are ascribed to a structural defect mitigation process both at the surface and in the bulk, resulting in improved crystal structure stability. In addition, the optimized particle size and the smaller BET surface area induced by the recrystallization contributes to the observed enhanced performance. Among the studied compositions, the heat treated Li$_2$Mn$_{2/3}$Ti$_{1/3}$O$_2$F sample displayed better electrochemical performance with a discharge capacity of 165 mAh g$^{−1}$ after 100 cycles at 0.1 C (∼80% of the initial capacity), when combined with further conditioning of the cells. The results point explicitly towards a guided stabilization approach, which could have a beneficial effect regarding the application of DRS oxyfluoride materials for sustainable LIBs

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

Tuning the Electronic and Electrochemical Properties of 3D Porous Laser‐Induced Graphene by Electrochemically Induced Deposition of Polyoxovanadate Nanoclusters for Flexible Supercapacitors

The advancement of microelectronic devices mandates the development of flexible energy storage systems to enable the fabrication of miniaturized and wearable electronics. Herein, a sustainable approach is demonstrated for tuning the electronic and electrochemical properties of hierarchically porous laser-induced graphene (LIG) substrates. The methodology entails the electro- chemical deposition of polyoxovanadate nanoclusters (K$_5$(CH$_3$CN)$_3$ [V$_{12}$O$_{32}$Cl] (= K$_5${V$_{12}$}) onto the highly porous LIG matrix. The comprehensive characterization is integrated through micro-Raman spectroscopy and in-depth X-ray photoelectron spectroscopy to elucidate the deposition mechanism and electronic properties of the fabricated electrode. The results indicate a significant correlation between the orientation of the deposited clusters and the non-crystalline regions of the LIG structure. Additionally, the cluster deposition results in a reduction of grain boundary defects in the nano-graphite lattice of LIG. The optimized electrode exhibits enhanced areal capacitance (C$_A$) of 125 mF cm$^{−2}$ at a current density of 0.1 mA cm$^{−2}$, representing a fivefold improvement compared to the undoped LIG substrate. Furthermore, as a proof of concept, a flexible solid-state symmetrical supercapacitor device, fabricated with a PVA-H$_2$ SO$_4$ gel electrolyte, demonstrates an areal capacitance of 24.92 mF cm$^{−2}$ at current density of 0.1 mA cm$^{−2}$ and exhibits exceptional cycling stability, enduring up to 5000 consecutive galvanostatic charge-discharge cycles

Mitigating Dissolution to Enhance the Performance of Pillar[5]quinone in Sodium Batteries

Sodium-ion batteries using organic electrode materials are a promising alternative to state-of-the-art lithium-ion batteries. However, their practical viability is hindered by challenges such as a low specific capacity of the organic electrode materials, or their dissolution in the electrolyte. We herein present a double mitigation strategy to enhance the performance of pillar[5]quinone (P5Q) as positive electrode material in sodium batteries. Using 5 m sodium bis(fluorosulfonyl)imide in succinonitrile as highly concentrated electrolyte, as well as encapsulating P5Q in CMK-3 (Carbon Mesostructured by KAIST with hexagonally ordered rod-like carbon domains) as templated ordered mesoporous carbon, we achieve a record cycling performance with improved cycling stability even at elevated temperature (40° C). The P5Q@CMK-3 composite electrode delivers 430 mAh g$_{-1}$ specific discharge capacity at 0.2 C rate with 90% retention over 200 cycles. This corresponds to an energy density of 831 Wh kg$_{-1}$ (based on P5Q mass) and surpasses previous reports on pillarquinones. When operated at 40° C, the P5Q@CMK-3 composite electrodes deliver a specific discharge capacity of 438 mAh g$_{-1}$ with 88 % capacity retention over 500 cycles (0.02 % per cycle). This study underscores the crucial role the electrolyte plays in advancing organic sodium batteries, offering a promising avenue for the future of sustainable energy technologies. A highly concentrated electrolyte of NaFSI in succinonitrile is used to mitigate the dissolution of pillar[5]quinone as electrode material for Na-ion batteries, encapsulated in CMK-3 as mesoporous carbon. This double mitigation strategy leads to a record cycling performance with improved cycling stability even at elevated temperature of 40° C. imag

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