Kothandam Krishnamoorthy

Electroless metal depositions are carried out by a series of reduction steps involving multiple metal ions to obtain a film on synthetic and natural substrates. Herein, we report the use of metal ions from a single element to deposit metal films on various substrates. In a typical metal deposition procedure, Pd²⁺ ions are anchored on a polycarbonate membrane with vertically aligned pores of 0.6 μm, which was reduced to its nanoparticles by sodium borohydride. The Pd nanoparticle-modified membrane was then immersed in a Pd plating bath. The Pd²⁺ ions are reduced by the reducing agent present in the plating bath. The reaction is catalyzed by the Pd nanoparticles. The Pd-modified membrane with vertically aligned Pd tubes were used to convert p-nitrophenol to p-aminophenol, which is an important molecule in the production of acetaminophen. While filtering the reactants through the Pd tubes, due to increased collision between the reactants and the catalyst Pd tubes, 100% conversion is achieved within 5 min. On the contrary, the conversion is only 10% if the membrane is placed in a vessel comprising the reactants. Due to the versatile nature of the metal deposition procedure, nickel was deposited on cotton substrates by a similar procedure. The nickel film-coated cotton cloth showed an impressive electromagnetic shielding interference efficiency of −60 dB while the uncoated cotton cloth did not shield electromagnetic radiation. To demonstrate the versatility of the approach, Pd-coated synthetic polymeric substrates are used to electroadhere gels and gel-like substances. Nickel-coated substrates are not suitable for electroadhesion; hence, a conjugated polymer was deposited on the substrate to electroadhere gel-like substances.

Graphite is the anode of choice for lithium-ion batteries. Due to volume change and poor conductivity of inorganic materials, they do not show comparable performance to that of graphite. Conjugated polymers are attractive because of their modularity and ease of synthesis. Herein, we report three polymers based on diketopyrrolopyrrole (DPP) as the anode. In an energy device, stored charges are due to a diffusive and capacitive component. Increasing the capacitive component is a challenge in both organic and inorganic systems. In our polymers, we installed urethane moieties that increase the capacitive component. The excellent Li⁺ ion transporting urethane moiety is part of the polymer chain. The Li⁺ ion transport is also impacted by the packing of the polymer chain. Therefore, the DPP units and urethane moieties are connected with either an alkyl chain, phenyl or biphenyl. The polymers with either alkyl or phenyl spacers showed stable cycling stability over 4000 charge-discharge cycles. On the other hand, the specific capacity of the batteries comprising a polymer with biphenyl started decreasing after 500 charge-discharge cycles. This is due to the solubility of the polymer in the battery electrolyte. The polymer with a phenyl spacer showed a higher Li⁺ ion diffusion coefficient due to the space generated between the polymer chains. The X-ray photoelectron spectroscopy analysis showed that the Li⁺ ions are bound to carbonyls, indicating the role of urethane in the charge transport. The polymer with an alkyl spacer showed a very high specific capacity of 600 mAh/g (1500th cycle) at a current density of 0.2 A/g, which is much higher than the theoretical capacity of graphite (372 mAh/g). The charge storage in all these polymers is dominated by a capacitive component, with the highest metric of 81% shown by a polymer with an alkyl spacer.

Polysulfides formed in Li–S batteries pose various characteristics. For example, Li ₂ S is solid while Li ₂ S ₄ is liquid. Li ₂ S is insoluble in battery electrolytes while Li ₂ S ₄ is soluble. All of them are negative charge bearing molecules. Lithium polysulfides are Lewis acids. Herein, a binder with multiple interaction motifs is presented to confine the polysulfides in the cathode. The base of the binder is sodium salt of carboxy methyl cellulose (CMC). β ‐cyclodextrin (CD) that comprises 21 hydroxyl groups is used because they hydrogen bond with the carboxylate moieties of CMC to impart mechanical strength to the binder to accommodate volume change during the sulfur to polysulfide conversion. Indeed, it is found that the binder with CD shows improved mechanical properties compared to CMC. The cavity of the CD is used to prepare an inclusion complex with ferrocene methanol. Due to the presence of Fe ²⁺ , the batteries comprising the inclusion complex show improved electrocatalytic properties. The Li–S batteries deliver a specific capacity of 780 mA h g ⁻¹ (1 C) at a high sulfur loading of 4.7 mg cm ⁻² and lean electrolyte (E/S of 5 μL mg ⁻¹ ).

Among the sodium battery electrolytes, sodium hexafluorophosphate (NaPF₆) exhibits superior conductivity, anodic stability, and stable cathode electrolyte interface compared to other electrolytes. Therefore, the synthesis of pure NaPF₆ through a simple process is very important. Usually, NaPF₆ is synthesized using HF. In our approach, NaPF₆ is synthesized by grinding dry ammonium hexafluorophosphate (NH₄PF₆) and sodium metal. Sodium injects an electron into the ammonium ion, which results in the formation of ammonia and hydrogen. The gram scale synthesis is completed in about 30 min. Purification of the product is not needed. The product purity is confirmed by various spectroscopic and electrochemical techniques. Usually, NaPF₆ comprises NaF, HF, and solvents as impurities that affect the performance of SIBs. It has been confirmed that the NaPF₆ synthesized by our mechanochemical approach in the absence of solvent is devoid of impurities despite the absence of product purification step. Furthermore, the synthesis of pure NaPF₆ (250 g) is demonstrated using a grinder used as household item in cooking Indian pancakes, which costs about 300 USD. The duration of the synthesis of 250 g pure NaPF₆ is 1 h. The purity of this sample is comparable to that of NaPF₆ (5 g) synthesized using mortar and pestle.

Lithium‐sulfur (Li─S) batteries are an attractive option for future energy storage devices because they offer higher theoretical specific capacity, energy density, and cost‐effectiveness than commercial lithium‐ion batteries. However, the practical applications of Li─S batteries are significantly limited by the shuttle effect caused by intermediate lithium polysulfides (LiPSs) and slow redox kinetics. In this study, the molecular engineering of chalcone‐linked, sp²‐bonded nanographene‐type covalent organic frameworks (COFs) as sulfur hosts is reported to enhance interactions with LiPSs, thereby effectively suppressing the shuttle effect. The developed sulfur‐hosting cathode material demonstrated outstanding battery performance, surpassing most reported materials by achieving a specific capacity of 1228 mA h g⁻¹ at 0.5C, with 80% retention after 500 cycles and an average Coulombic Efficiency (C.E.) of 99%. Additionally, the mechanisms of sulfur immobilization, the subsequent conversion into lithium polysulfides (LiPSs), and their binding energies with COFs are investigated using density functional theory (DFT) calculations. These findings offer valuable insights into the structure‐property relationships essential for developing more efficient sulfur‐hosting cathodes.

Sulfur undergoes various changes, including the formation of negative charge-bearing lithium polysulfides during the operation of Li-S batteries. Dissolution of some of the polysulfides in battery electrolytes is one of the reasons for the poor performance of Li-S batteries. The charge injection into the sulfur and polysulfides from the electrode is also a problem. To address these issues, a small-molecule additive, 3,6-di(pyridin-4-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione, was designed and synthesized with carbonyl oxygen atoms and two types of nitrogen. The pyridinic nitrogen increases the electronegativity of the carbonyl oxygen atoms. The pyridinic nitrogen, carbonyl oxygen, and lactam nitrogen provide multiple binding sites concurrently to the polysulfides, which increases the binding efficiency between the additive and polysulfides. A control molecule without the pyridine moiety displayed decreased binding to lithium polysulfides. Furthermore, the band edges of lithium polysulfide and 3,6-di(pyridin-4-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione are commensurate for efficient charge transfer between them, leading to the efficient electrocatalysis of lithium polysulfides. The cyclic voltammogram of the Li-S battery fabricated with 3,6-di(pyridin-4-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione exhibited sharp and well-defined peaks, confirming the formation of Li₂S_y (where y varies between one and eight) from S₈. These Li-S batteries showed a specific capacity of 950 mA h/g at 0.5 C, with a capacity retention of 70% at the 300th cycle. The pyridine-free control molecule, 3,6-diphenyl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione, showed relatively poor performance in a Li-S battery.