Reaction of Amino-Terminated PAMAM Dendrimers with Carbon Dioxide in Aqueous and Methanol Solutions

Polyamines have been used as active materials to capture carbon dioxide gas based on its well-known reaction with amines to form carbamates. This work investigates the reactions between three amino-terminated poly(amidoamine) (PAMAM) dendrimers (G1, G3 and G5) and CO2(g) in aqueous (D2O) and methanolic (CD3OD) solutions. The reactions were monitored using 1H NMR spectroscopy, and yielded dendrimers with a combination of terminal carbamate and terminal ammonium groups. In aqueous media the reaction was complicated by the generation of soluble carbonate and bicarbonate ions. The reaction was cleaner in CD3OD, where the larger G5 dendrimer solution formed a gel upon exposure to CO2(g). All reactions were reversible, and the trapped CO2 could be released by treatment with N2(g) and mild heating. These results highlight the importance of the polyamine dendrimer size in terms of driving changes to the solution’s physical properties (viscosity, gel formation) generated by exposure to CO2(g).

Review— A Review on the Anode and Cathode Materials for Lithium-Ion Batteries with Improved Subzero Temperature Performance

Lithium-ion batteries (LiBs) have been widely used in a variety of applications, however they still suffer from low capacity retention, large capacity fade ratio or inability to charge efficiently at low temperatures, especially below -20 oC. The reasons behind these drawbacks originate from the nature of active materials such as the anode and the cathode, along with the composition of electrolyte solutions. In particular, from the perspective of active materials, it has been reported that the most common problems arise from the dramatic increase in the resistances, especially charge transfer resistance, and the decrease of lithium-ion diffusivity, by more than one order of magnitude. In this report, we review the most recent strategies in the development of anode and cathode materials and composites, focusing on enhanced electronic and ionic conductivities for improved low-temperature electrochemical performance. Our overview aims to provide a comprehensive comparative study of the proposed methods to overcome the low-temperature challenges in order to develop high energy-density LiBs with enhanced capacity retention, cycling stability and high-rate capability under extreme conditions.

Performance of Cathodes Fabricated from Mixture of Active Materials Obtained from Recycled Lithium-Ion Batteries

The cathode performance of lithium-ion batteries (LIBs) fabricated from recycled cathode active materials is studied for three scenarios. These scenarios are based on the conditions for separation of different cathode active materials in recycling facilities during the LIB’s recycling process. In scenario one, the separation process is performed ideally, and the obtained pure single cathode active material is used to make new LIBs after regeneration. In scenario two, the separation of active materials is performed with efficiencies of less than 100%, which is the actual case in the recycling process. In this scenario, a single cathode active material that contains a little of the other types of cathode active materials is used to make new LIBs after the materials’ regeneration. In scenario three, the separation has not been performed during the recycling process. In this scenario, all types of cathode active materials are regenerated together, and a mixture is used to make new LIBs. The studies are performed through modeling and computer simulation, and several experiments are conducted for validation purposes. The cathode active materials that are studied are the five commercially available cathodes made of LiMn2O4 (LMO), LiCoO2 (LCO), LiNixMnyCo(1−x−y)O2 (NMC), LiNixCoyAl(1−x−y)O2 (NCA), and LiFePO4 (LFP). The results indicate that the fabrication of new LIBs with a mixture of cathode active materials is possible when cathode active materials are not ideally separated from each other. However, it is recommended that the separation process is added to the recycling process, at least for the separation of LFP or reducing its amount in the cathode active materials mixture. This is because of the difference of the voltage level of LFP compared to the other studied active materials for cathodes.

Practical Quinone-Based Organic Supercapacitor > 6 V

Inexpensive, high-performing, and environmentally friendly energy storage devices are required for smart grids that efficiently utilize renewable energy. Energy storage devices consisting of organic active materials are promising because organic materials, especially quinones, are ubiquitous and usually do not require harsh conditions for synthesis, releasing less CO2 during mass production. Although fundamental research-scale aqueous quinone-based organic supercapacitors have shown excellent energy storage performance, no practical research has been conducted. We aimed to develop a practical-scale aqueous-quinone-based organic supercapacitor. By connecting 12 cells of size 10 cm × 10 cm × 0.5 cm each in series, we fabricated a high-voltage (> 6 V) aqueous organic supercapacitor that can charge a smartphone at a 1 C rate. This is the first step in commercializing aqueous organic supercapacitors that could solve environmental problems, such as high CO2 emissions, air pollution by toxic metals, and limited electricity generation by renewable resources.

Synergistic effect of p-type and n-type dopants in semiconductors for efficient electrocatalytic water splitting

The main challenge for acidic water electrolysis is the lack of active and stable oxygen evolution catalysts based on abundant materials, which are globally scalable. Iridium oxide is the only material, which is active and stable. However, Ir is extremely rare and far from scalable. There exist both active materials and stable materials, but those that are active are not stable and vice versa. In this work, we present a strategy for making stable materials active. The stable materials are semiconductors that cannot change oxidation state at relevant reaction conditions. Based on DFT calculations, we find that by adding an n-type dopant, semiconductor surfaces can bind oxygen. However, after oxygen is adsorbed, the material is again in a state where it cannot bind or desorb oxygen. By combining n-type and p-type dopants, the reactivity can be tuned so that oxygen can be adsorbed and desorbed under reaction conditions. It turns out that the tuning can be understood from the electrostatic interactions between the dopants as well as between the dopants and the binding site. We experimentally verify that this strategy works in TiO2 by co-doping with different pairs of n- and p-type dopants. This encourages that the co-doping approach can be used to activate stable materials, without intrinsic oxygen evolution activity, to discover new catalysts for acid water electrolysis.

A Photo-responsive p-Si/TiO2/Ag Heterostructure with Charge Transfer for Recyclable Surface-Enhanced Raman Scattering Substrate

Semiconductor - metal heterostructure is an attractive Surface-Enhanced Raman Scattering (SERS) -active materials, which can boost the performance effectively because of the synergistic contribution of Electromagnetic (EM) and charge transfer...

Photocatalytic polymer nanomaterials for the production of high value compounds

Nanotechnology has provided a platform for producing new photocatalytic materials, where the reduction in length scales has been used to amplify the efficiency of these light active materials. The progression...