The rechargeable magnesium (Mg) battery has been considered a promising candidate for future battery generations due to unique advantages of the Mg metal anode. The combination of Mg with a sulfur cathode is one of the attractive electrochemical energy storage systems that use safe, low-cost, and sustainable materials and could potentially provide a high energy density. To develop a suitable electrolyte remains the key challenge for realization of a magnesium sulfur (Mg–S) battery. Herein, we demonstrate that magnesium tetrakis­(hexafluoroisopropyloxy) borate Mg­[B­(hfip)4]2 (hfip = OC­(H)­(CF3)2) satisfies a multitude of requirements for an efficient and practical electrolyte, including high anodic stability (>4.5 V), high ionic conductivity (∼11 mS cm–1), and excellent long-term Mg cycling stability with a low polarization. Insightful mechanistic studies verify the reversible redox processes of Mg–S chemistry by utilizing Mg­[B­(hfip)4]2 electroylte and also unveil the origin of the voltage hysteresis in Mg–S batteries.

Here we report for the first time the development of a Mg rechargeable battery using a graphene-sulfur nanocomposite as the cathode, a Mg-carbon composite as the anode and a non-nucleophilic Mg based complex in tetraglyme solvent as the electrolyte. The graphene-sulfur nanocomposites are prepared through a new pathway by the combination of thermal and chemical precipitation methods. The Mg/S cell delivers a higher reversible capacity (448 mA h g(-1)), a longer cyclability (236 mA h g(-1) at the end of the 50(th) cycle) and a better rate capability than previously described cells. The dissolution of Mg polysulfides to the anode side was studied by X-ray photoelectron spectroscopy. The use of a graphene-sulfur composite cathode electrode, with the properties of a high surface area, a porous morphology, a very good electronic conductivity and the presence of oxygen functional groups, along with a non-nucleophilic Mg electrolyte gives an improved battery performance.

A novel synthesis procedure is devised to obtain nitrogen‐doping in hydrogen‐exfoliated graphene (HEG) sheets. An anionic polyelectrolyte–conducting polymer duo is used to form a uniform coating of the polymer over graphene sheets. Pyrolysis of graphene coated with polypyrrole, a nitrogen‐containing polymer, in an inert environment leads to the incorporation of nitrogen atoms in the graphene network with simultaneous removal of the polymer. These nitrogen‐doped graphene (N‐HEG) sheets are used as catalyst support for dispersing platinum and platinum–cobalt alloy nanoparticles synthesized by the modified‐polyol reduction method, yielding a uniform dispersion of the catalyst nanoparticles. Compared to commercial Pt/C electrocatalyst, Pt–Co/N‐HEG cathode electrocatalyst exhibits four times higher power density in proton exchange membrane fuel cells, which is attributed to the excellent dispersion of Pt–Co alloy nanoparticles on the N‐HEG support, the alloying effect of Pt–Co, and the high electrocatalytic activity of the N‐HEG support. A stability study shows that Pt/N‐HEG and Pt–Co/N‐HEG cathode electrocatalysts are highly stable in acidic media. The study shows two promising electrocatalysts for proton exchange membrane fuel cells, which on the basis of performance and stability present the possibility of replacing contemporary electrocatalysts.

We report a novel way of synthesizing graphene-carbon nanotube hybrid nanostructure as an anode for lithium (Li) ion batteries. For this, graphene was prepared by the solar exfoliation of graphite oxide, while multiwalled carbon nanotubes (MWNTs) were prepared by the chemical vapor deposition method. The graphene-MWNT hybrid nanostructure was synthesized by first modifying graphene surface using a cationic polyelectrolyte and MWNT surface with acid functionalization. The hybrid structure was obtained by homogeneous mixing of chemically modified graphene and MWNT constituents. This hybrid nanostructure exhibits higher specific capacity and cyclic stability. The strengthened electrostatic interaction between the positively charged surface of graphene sheets and the negatively charged surface of MWNTs prevents the restacking of graphene sheets that provides a highly accessible area and short diffusion path length for Li-ions. The higher electrical conductivity of MWNTs promotes an easier movement of the electrons within the electrode. The present synthesis scheme recommends a new pathway for large-scale production of novel hybrid carbon nanomaterials for energy storage applications and underlines the importance of preparation routes followed for synthesizing nanomaterials.

The development of multivalent metal (such as Mg and Ca) based battery systems is hindered by lack of suitable cathode chemistry that shows reversible multi‐electron redox reactions. Cationic redox centres in the classical cathodes can only afford stepwise single‐electron transfer, which are not ideal for multivalent‐ion storage. The charge imbalance during multivalent ion insertion might lead to an additional kinetic barrier for ion mobility. Therefore, multivalent battery cathodes only exhibit slope‐like voltage profiles with insertion/extraction redox of less than one electron. Taking VS 4 as a model material, reversible two‐electron redox with cationic–anionic contributions is verified in both rechargeable Mg batteries (RMBs) and rechargeable Ca batteries (RCBs). The corresponding cells exhibit high capacities of >300 mAh g −1 at a current density of 100 mA g −1 in both RMBs and RCBs, resulting in a high energy density of >300 Wh kg −1 for RMBs and >500 Wh kg −1 for RCBs. Mechanistic studies reveal a unique redox activity mainly at anionic sulfides moieties and fast Mg 2+ ion diffusion kinetics enabled by the soft structure and flexible electron configuration of VS 4 .

The efforts to push proton exchange membrane fuel cells (PEMFC) for commercial applications are being undertaken globally. In PEMFC, the sluggish kinetics of oxygen reduction reactions (ORR) at the cathode can be improved by the alloying of platinum with 3d-transition metals (TM = Fe, Co, etc.) and with nitrogen doping, and in the present work we have combined both of these aspects. We describe a facile method for the synthesis of a nitrogen doped (reduced graphene oxide (rGO)-multiwalled carbon nanotubes (MWNTs)) hybrid structure (N-(G-MWNTs)) by the uniform coating of a nitrogen containing polymer over the surface of the hybrid structure (positively surface charged rGO-negatively surface charged MWNTs) followed by the pyrolysis of these (rGO-MWNTs) hybrid structure-polymer composites. The N-(G-MWNTs) hybrid structure is used as a catalyst support for the dispersion of platinum (Pt), platinum-iron (Pt3Fe) and platinum-cobalt (Pt3Co) alloy nanoparticles. The PEMFC performances of Pt-TM alloy nanoparticle dispersed N-(G-MWNTs) hybrid structure electrocatalysts are 5.0 times higher than that of commercial Pt-C electrocatalysts along with very good stability under acidic environment conditions. This work demonstrates a considerable improvement in performance compared to existing cathode electrocatalysts being used in PEMFC and can be extended to the synthesis of metal, metal oxides or metal alloy nanoparticle decorated nitrogen doped carbon nanostructures for various electrochemical energy applications.

Li‐garnets are promising inorganic ceramic solid electrolytes for lithium metal batteries, showing good electrochemical stability with Li anode. However, their brittle and stiff nature restricts their intimate contact with both the electrodes, hence presenting high interfacial resistance to the ionic mobility. To address this issue, a strategy employing ionic liquid electrolyte (ILE) thin interlayers at the electrodes/electrolyte interfaces is adopted, which helps overcome the barrier for ion transport. The chemically stable ILE improves the electrodes‐solid electrolyte contact, significantly reducing the interfacial resistance at both the positive and negative electrodes interfaces. This results in the more homogeneous deposition of metallic lithium at the negative electrode, suppressing the dendrite growth across the solid electrolyte even at high current densities of 0.3 mA cm−2. Further, the improved interface Li/electrolyte interface results in decreasing the overpotential of symmetric Li/Li cells from 1.35 to 0.35 V. The ILE modified Li/LLZO/LFP cells stacked either in monopolar or bipolar configurations show excellent electrochemical performance. In particular, the bipolar cell operates at a high voltage (≈8 V) and delivers specific capacity as high as 145 mAh g−1 with a coulombic efficiency greater than 99%.

This work investigates the electrochemical processes in Magnesium/Sulfur rechargeable batteries with a new cathode design by operando Raman and impedance spectroscopy.