Mg batteries have the advantages of resource abundance, high volumetric energy density, and dendrite-free plating/stripping of Mg anodes. However the injection of highly polar Mg cannot maintain the structural integrity of intercalation-type cathodes even for open framework prototypes. The lack of high-voltage electrolytes and sluggish Mg diffusion in lattices or through interfaces also limit the energy density of Mg batteries. Mg-S system based on moderate-voltage conversion electrochemistry appears to be a promising solution to high-energy Mg batteries. However, it still suffers from poor capacity and cycling performances so far. Here, a ZIF-67 derivative carbon framework codoped by N and Co atoms is proposed as effective S host for highly reversible Mg-S batteries even under high rates. The discharge capacity is as high as ≈600 mA h g at 1 C during the first cycle, and it is still preserved at ≈400 mA h g after at least 200 cycles. Under a much higher rate of 5 C, a capacity of 300-400 mA h g is still achievable. Such a superior performance is unprecedented among Mg-S systems and benefits from multiple factors, including heterogeneous doping, Li-salt and Cl addition, charge mode, and cut-off capacity, as well as separator decoration, which enable the mitigation of electrode passivation and polysulfide loss.

Water electrolysis is a sustainable technology for hydrogen production since this process can utilize the intermittent electricity generated by renewable energy such as solar, wind, and hydro. However, the large‐scale application of this process is restricted by the high electricity consumption due to the large potential gap (>1.23 V) between the anodic oxygen evolution reaction and the cathodic hydrogen evolution reaction (HER). Herein, a novel and efficient hydrogen production system is developed for coupling glucose‐assisted Cu(I)/Cu(II) redox with HER. The onset potential of the electrooxidation of Cu(I) to Cu(II) is as low as 0.7 VRHE (vs reversible hydrogen electrode). In situ Raman spectroscopy, ex situ X‐ray photoelectron spectroscopy, and density functional theory calculation demonstrates that glucose in the electrolyte can reduce the Cu(II) into Cu(I) instantaneously via a thermocatalysis process, thus completing the cycle of Cu(I)/Cu(II) redox. The assembled electrolyzer only requires a voltage input of 0.92 V to achieve a current density of 100 mA cm−2. Consequently, the electricity consumption for per cubic H2 produced in the system is 2.2 kWh, only half of the value for conventional water electrolysis (4.5 kWh). This work provides a promising strategy for the low‐cost, efficient production of high‐purity H2.

A magnesium battery is a promising candidate for large-scale transportation and stationary energy storage due to the security, low cost, abundance, and high volumetric energy density of a Mg anode. But there are still some obstacles retarding the wide application of Mg batteries, including poor kinetics of Mg-ion transport in lattices and low theoretical capacity in inorganic frameworks. A Mg-Li dual-salt electrolyte enables kinetic activation by dominant intercalation of Li-ions instead of Mg-ions in cathode lattices without the compromise of a stable Mg anode process. Here we propose a Mg-organic battery based on a renewable rhodizonate salt ( e. g., NaCO) activated by a Mg-Li dual-salt electrolyte. The nanostructured organic system can achieve a high reversible capacity of 350-400 mAh/g due to the existence of high-density carbonyl groups (C═O) as redox sites. Nanocrystalline NaCO wired by reduced graphene oxide enables a high-rate performance of 200 and 175 mAh/g at 2.5 (5 C) and 5 A/g (10 C), respectively, which also benefits from a high intrinsic diffusion coefficient (10-10 cm/s) and pesudocapacitance contribution (>60%) of NaCO for Li-Mg co-intercalation. The suppressed exfoliation of CO layers by a firmer non-Li pinning via Na-O-C or Mg-O-C and a dendrite-resistive Mg anode lead to a long-term cycling for at least 600 cycles. Such an extraordinary capacity/rate performance endows the Mg-NaCO system with high energy and power densities up to 525 Wh/kg and 4490 W/kg (based on active cathode material), respectively, exceeding the level of high-voltage insertion cathodes with typical inorganic structures.

Large-capacity conversion electrodes are highly required to raise the energy density of batteries. However, their undesired phase segregation and volume expansion during cycling lead to the motivation for nanofabrication and nanochemistry of active species in order to decrease "dead mass" and promote better construction of conductive networks. However, the inactivity of the conductive skeleton and loose nanostructure would compromise the energy density of the electrode. The integration of large-sized (high-density) grains into an electroactive conductive network in a compact way is still a big challenge. Here we report a proof-of-concept prototype consisting of unusual MoS solid bubbles of hundreds of nanometers in size, which are conformally encapsulated by thin-layer carbon. The seamless welding between this carbon coating and the surrounding broader carbon substrate can effectively avoid the peel-off of active species and breakage of the conductive network. This MoS-C composite is achieved by simultaneous self-sulfuration and self-carbonization of a polyoxometalate (POM)-based chelate, and its Li-storage performance is superior to most MoS-based anodes even with ultrathin 2D nanosheets. Partially benefiting from the electroactivity of a dithiooxamide (DTO)-derivate carbon network, the reversible capacity of MoS-C by pyrolyzing the POM-DTO chelate can reach 1500-2000 mAh/g at 0.5-1 A/g even after 700 cycles and be maintained around 1000 mAh/g under as high as 10-20 A/g.