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.

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It is of great importance to improve the proton conductivity of proton exchange membranes by easy-handling and cost-efficient approaches. In this work, we incorporated a commercially obtained surfactant, sodium dodecyl benzene sulfonate (SDBS), into sulfonated poly(ether ether ketone) (SPEEK) through solution casting to prepare SPEEK/SDBS membranes. When no more than 10 wt % SDBS was added, the SDBS was well dissolved into the SPEEK matrix, and the activation energy for the proton transfer in the SPEEK/SDBS membranes was greatly reduced, leading to significant enhancement of the membrane proton conductivity. Compared with the SPEEK control membrane, the SPEEK/SDBS membrane with 10 wt % SDBS showed a 78% increase in proton conductivity, up from 0.051 S cm−1 to 0.091 S cm−1, while the water uptake increased from 38% to 62%. Moreover, the SPEEK/SDBS membrane exhibited constant proton conductivity under a long-term water immersion test.

In this work, sulfonated poly(ether ether ketone) (SPEEK) nanocomposite membranes were prepared with high loading of phosphotungstic acid (HPW) anchored on imidazole-functionalized halloysite nanotubes (mHNTs), which were synthesized via bio-inspired dopamine self-polymerization and dopamine-initiated atom transfer radical polymerization (ATRP) process. The SPEEK/mHNTs/HPW nanocomposite membranes demonstrated dense and uniform morphology where both mHNTs and HPW were well dispersed. Due to the strong acid-base interactions between HPW and imidazole groups of mHNTs, HPW was successfully immobilized on the surfaces of high aspect-ratio mHNTs, resulting in more active sites and shorter distance for proton hopping. Membrane proton conductivity was greatly improved and the activation energy for the proton transfer was significantly reduced. The proton conductivity of the SPEEK/mHNTs/HPW nanocomposite membrane with 42.9 wt% HPW was 82% higher than that of SPEEK control membrane, and remained almost constant for more than 1000 h under immersion in liquid water.

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