Rechargeable metal−sulfur batteries (RMSBs) represent one of the most attractive electrochemical systems in terms of energy density and cost. In most of the proposed systems, the anode side is metallic and the cathode side is elemental sulfur impregnated in a porous matrix. Despite the relatively low voltage of these systems, they attract a lot of attention and are considered to be very promising as nextgeneration batteries for the following reasons: (1) utilization of active metal anodes enables a leap in specific energy due to the high capacity of metal anodes in comparison to intercalation compounds, (2) sulfur as a cathode exhibits high theoretical specific capacity (1675 mAh/g), and (3) system components make RMSBs low-cost, less toxic batteries. Nevertheless, the high reactivity of metallic anodes (e.g., Li, Na, Mg, and Al) and the solubility of sulfur species in the electrolyte render these batteries unstable and hinder their practical realization. In this Perspective, we focus on rechargeable sulfur batteries with active metal anodes, present important studies conducted in this field, and summarize the reported methods and techniques that are mandatory for effective and practical studies of RMSB.

Rechargeable magnesium batteries (RMBs) have attracted a lot of attention in recent decades due to the theoretical properties of these systems in terms of energy density, safety, and price. Nevertheless, to date, fully rechargeable magnesium battery prototypes with sufficient longevity and reversibility were realized only with low voltage and low capacity intercalation cathode materials based on Cheverel phases. The community is therefore actively looking for high-capacity cathodes that can work with metallic magnesium anodes in viable RMB systems. One of the most promising cathode materials, in terms of very high theoretical specific capacity, is, naturally, sulfur. A number of recent works studied the electrochemical performances of rechargeable sulfur cathodes in RMB, with success to some extent on the cathode side. Nevertheless, as known from the lithium−sulfur rechargeable battery systems, the formation of soluble polysulfides during discharge affects strongly the behavior of the anode side. In this article and the work it describes, we focus on soluble polysulfides impact on Mg−S electrochemichal systems. We carefully designed herein conditions that mimic the Mg−S battery prototypes containing balanced Mg and elemental sulfur electrodes. Under these conditions, we extensively studied the Mg anode behavior. The study shows that when elemental sulfur cathodes are discharged in the Mg−S cells containing electrolyte solutions in which Mg anodes behave reversibly, the polysulfide species thus formed migrate to the anode and eventually fully passivate it by the formation of very stable surface layers. The work involved electrochemical, spectroscopic, and microscopic studies. The present study clearly shows that to realize practical rechargeable Mg−S batteries, the transport of any sulfide moieties from the sulfur cathode to the magnesium anode has to be completely avoided. Such a condition is mandatory for the operation of secondary Mg−S batteries.

The oxidation level and properties of reduced graphene oxides (rGOs) were fine-tuned using temperature-programmed reductive annealing. rGOs were annealed at different temperatures (from 500 to 1000 °C) in hydrogen to modulate their oxidation levels. The surface of the rGOs was fully characterized using electron paramagnetic resonance backed by Raman, X-ray diffraction, and chemical analysis measurements. These experiments were used to study the changes in the surface of the rGO, its surface functionalities, and its defects as a function of the reduction temperature. In addition, electrochemical measurements to quantify the oxidation level of the rGOs offer a simple tool to correlate the properties of rGOs with their structure. Finally, we explored the effect of different levels of reduction on conductivity, capacitance, and surface reactivity. This research offers simple methodological techniques and routes to control and characterize the oxidation level of bulk quantities of rGO.

The number of patients suffering from inflammatory bowel disease (IBD) is increasing worldwide. The development of noninvasive tests that are rapid, sensitive, specific, and simple would allow preventing patient discomfort, delay in diagnosis, and the follow-up of the status of the disease. Herein, we show the interest of vertically aligned nitrogen-doped carbon nanotube (VA-NCNT) electrodes for the required sensitive electrochemical detection of lysozyme in serum, a protein that is up-regulated in IBD. To achieve selective lysozyme detection, biotinylated lysozyme aptamers were covalently immobilized onto the VA-NCNTs. Detection of lysozyme in serum was achieved by measuring the decrease in the peak current of the Fe(CN)6(3-/4-) redox couple by differential pulse voltammetry upon addition of the analyte. We achieved a detection limit as low as 100 fM with a linear range up to 7 pM, in line with the required demands for the determination of lysozyme level in patients suffering from IBD. We attained the sensitive detection of biomarkers in clinical samples of healthy patients and individuals suffering from IBD and compared the results to a classical turbidimetric assay. The results clearly indicate that the newly developed sensor allows for a reliable and efficient analysis of lysozyme in serum.

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