Room temperature sodium–sulfur (Na–S) batteries are severely hampered by dissolution of polysulfides into electrolytes. Herein, a facile approach is used to tune a biomass-derived carbon down to an ultrasmall 0.37 nm microporous structure for the first time as a cathode in sodium–sulfur batteries. This produced an intact uniform Na₂S membrane to greatly confine the dissolution of polysulfides while realizing a direct solid phase conversion for complete reduction of sulfur to Na₂S, which delivers a sulfur loading of 1 mg cm⁻² (50 wt.%), an excellent rate capacity (933 mAh g⁻¹ @ 0.1 A g⁻¹ and 410 mAh g⁻¹ @ 2 A g⁻¹), long cycle performance (0.036% per cycle decay at 1 A g⁻¹ after 1500 cycles), and a high energy density for 373 Wh kg⁻¹ (0.1 A g⁻¹) based on whole electrode weight (active sulfur loading + carbon), ranking the best among all reported plain carbon cathode-based room temperature sodium–sulfur batteries in terms of the cycle life and rate capacity. It is proposed that the solid Na₂S produced in the ultrasmall pores (0.37 nm) can be squeezed out to grow an intact membrane on the electrode surface covering the outlet of the pores and greatly depressing the dissolution effect of polysulfides for the long cycle life. This work provides a green chemistry to recycle wastes for sustainable energies and sheds light on design of a unique pore structure to effectively block the dissolution of polysulfides for high-performance sodium–sulfur batteries.

Pore structure plays critical roles in electrode kinetics but very challenging to tailor porous nanowires with rationally distributed pore sizes in a bioelectrochemical system. Herein a hierarchically porous nanowires-material is delicately tuned for an optimal pore structure by adjusting the weight percentage of SiO₂-hard template in an electrospinning precursor solution. The as-prepared optimal electrospinning nanowires further used as an anode of microbial fuel cells (MFCs), delivering a maximum output power density of 1,407.42 mW·m⁻² with 4.24 and 10 times higher than that of the non-porous fiber and carbon cloth anode, respectively. The great enhancement is attributed to the rational pore structure which offers the largest surface area while the rich-mesopores well match with the size of electron mediators for a high density of catalytic centers. This work provides thoughtful insights to design of hierarchical porous electrode for high-performance MFCs and other bioelectrochemical system devices.

Metal-ion capacitors could merit advantages from both batteries and capacitors, but they need to overcome the severe restrictions from their sluggish reaction kinetics of the battery type electrode and low specific capacitance of capacitor type electrode for both high energy and power density. Herein, we use the Kirkendall effect for the first time to synthesize unique tubular hierarchical molybdenum dioxide with encapsulated nitrogen-doped carbon sheets while in situ realizing phosphorus-doping to create rich oxygen vacancies (P-MoO_2-x@NP-C) as a sodium-ion electrode. Experimental and theoretical analysis confirm that the P-doping introduced oxygen defects can partially convert the high-bond-energy Mo–O to low-bond-energy Mo–P, resulting in a low oxidation state of molybdenum for enhanced surface reactivity and rapid reaction kinetics. The as-prepared P-MoO_2-x@NP-C as an ion-battery electrode is further used to pair active N-doped carbon nanosheet (N-C-A) electrode for Na-ion hybrid capacitor, delivering excellent performance with an energy density of 140.3 Wh kg⁻¹, a power density of 188.5 W kg⁻¹ and long stable life in non-aqueous solution, which ranks the best among all reported MoO_x-based hybrid capacitors. P-MoO_2-x@NP-C is also used to fabricate a zinc-ion hybrid capacitor, also accomplishing a remarkable energy density of 43.8 Wh kg⁻¹, a power density of 93.9 W kg⁻¹, and a long stable life@2A g⁻¹ of 32000 cycles in aqueous solutions, solidly verifying its universal significance. This work not only demonstrates an innovative approach to synthesize high-performance metal ion hybrid capacitor materials but also reveals certain scientific insights into electron transfer enhancement mechanisms.

Using porous carbon hosts in cathodes of Li-S cells can disperse S actives and offset their poor electrical conductivity. However, such reservoirs would in turn absorb excess electrolyte solvents to S-unfilled regions, causing the electrolyte overconsumption, specific energy decline, and even safety hazards for battery devices. To build better cathodes, we propose to substitute carbons by In-doped SnO₂ (ITO) nano ceramics that own three-in-one functionalities: 1) using conductive ITO enables minimizing the total carbon content to an extremely low mass ratio (~3%) in cathodes, elevating the electrode tap density and averting the electrolyte overuse; 2) polar ITO nanoclusters can serve as robust anchors toward Li polysulfide (LiPS) by electrostatic adsorption or chemical bond interactions; 3) they offer catalysis centers for liquid–solid phase conversions of S-based actives. Also, such ceramics are intrinsically nonflammable, preventing S cathodes away from thermal runaway or explosion. These merits entail our configured cathodes with high tap density (1.54 g cm⁻³), less electrolyte usage, good security for flame retardance, and decent Li-storage behaviors. With lean and LiNO₃-free electrolyte, packed full cells exhibit excellent redox kinetics, suppressed LiPS shuttling, and excellent cyclability. This may trigger great research enthusiasm in rational design of low-carbon and safer S cathodes.

The environment benignity and battery cost are major concerns for grid-scale energy storage applications. The emerging dendrite-free Fe-ion aqueous batteries are promising due to the rich natural abundance, low cost and non-toxicity for Fe resources. However, serious passivation reactions on Fe anodes and poor long-term cyclability for matched cathodes still stand in the way for their practical usage. To settle above constraints, we herein use NH₄Cl as the electrolyte regulator to elevate the reaction kinetics of passivated Fe anodes, and also propose a special cathode-free design to prolong the cells lifetime over 1,000 cycles. The added NH₄Cl can erode/break inert passivation layers and strengthen the ion conductivity of electrolytes, facilitating the reversible Fe plating/ stripping and Fe²⁺ shuttling. The highly puffed nano carbon foams function as current collectors and actives anchoring hosts, enabling expedite Fe²⁺ adsorption/desorption, Fe^II/Fe^III redox conversions and Fe^III deposition. The configured rocking-chair Fe-ion cells have good environmental benignity and decent energy-storage behaviors, including high reactivity/reversibility, outstanding cyclic stability and far enhanced operation longevity. Such economical, long-cyclic and green cathode-free Fe-ion batteries may hold great potential in near-future energy-storage power stations.

It is critical for fabricating flexible biosensors with both high sensitivity and good selectivity to realize real-time monitoring superoxide anion (O₂^•−), a specific reactive oxygen species that plays critical roles in various biological processes. This work delicately designs a Mn₃(PO₄)₂/MXene heterostructured biomimetic enzyme by assembling two-dimensional (2-D) Mn₃(PO₄)₂ nanosheets with biomimetic activity and 2-D MXene nanosheets with high conductivity and abundant functional groups. The 2-D nature of the two components with strong interfacial interaction synergistically enables the heterostructure an excellent flexibility with retained 100% of the response when to reach a bending angle up to 180°, and 96% of the response after 100 bending/relaxing cycles. It is found that the surface charge state of the heterostructure promotes the adsorption of O₂^•−, while the high-energy active site improves electrochemical oxidation of O₂^•−. The Mn₃(PO₄)₂/MXene as a sensing platform towards O₂^•− achieves a high sensitivity of 64.93 μA·μM⁻¹·cm⁻², a wide detection range of 5.75 nM to 25.93 μM, and a low detection limit of 1.63 nM. Finally, the flexible heterostructured sensing platform realizes real-time monitoring of O₂^•− in live cell assays, offering a promising flexible biosensor towards exploring various biological processes.