Bioinspired mineralization is a powerful method for designing and preparing nanomaterials. In this work, we developed a bioinspired mineralization approach under freezing conditions and fabricated methyl cellulose (MC)/NaHCO3 flake precursors with a sophisticated hierarchical structure. Based on this, amazing wing-like porous carbon sheets (WPCSs) assembled by numerous interconnected hollow carbon bubbles were obtained after carbonization and removal of inorganic crystals, which are seldom obtained by other artificial methods. Benefiting from their open framework, large surface area, and enlarged interlayer spacing of graphitized nanocrystallites, the obtained WPCSs exhibited an obvious boost in potassium storage performance. As an anode of potassium-ion batteries, they showed high reversible capacities of 347 mAh g–1 at 50 mA g–1 and 122 mAh g–1 at 20 A g–1 and relatively stable cyclability for 3000 cycles. The assembled WPCS//WPCS potassium-ion hybrid supercapacitor delivered a high energy density of 108 Wh kg–1 at a power density of 280 W kg–1. Given the cost effectiveness and green process, the modified bioinspired mineralization under freezing conditions would provide a facile and green way for exploring porous carbons with controlled structures and rich multifunction.

lithium resources greatly limits the large-scale promotion and application of LIBs. [4-7] As possible candidates, sodium and potassium ion systems are receiving intense attention owing to their low cost and high natural abundant resources. [8-14] Particularly, recent studies indicated that compared with sodium ions, potassium ions exhibited more merits on the basis of its similar intercalation behaviors in graphite and closer redox potential (K/K + , −2.92 V) with Li ions. [15,16] Therefore, potassium ion energy storage system, including potassium ion batteries (PIBs) and potassium ion hybrid capacitors (PIHCs) demonstrates a promising prospect in practical applications, and the corresponding studying upsurge is just beginning. [16,17] In the exploration of potassium electrode materials, porous carbons are highly preferable owing to their elastic framework, rich porosity and good conductivity, which can efficiently alleviate the volume expansion caused by the larger K + (ionic radius, 1.38 Å) intercalation and provides more pathways for fast K + diffusion. [16,18-21] So far, many carbons with various porosities have been successfully used in potassium ion system, exhibiting excellent electrochemical performance. [22,23] In current strategies of producing porous carbons, the template method is considered as one ideal way owing to its good control of porous architectures. [16] Presently, solid-phase templates including salts, SiO 2 nanospheres, and metal foams have been applied widely in constructing porous carbons. [24-26] Besides, gas-phase templates such as gas bubbles and foams are also popular due to their facile and economical process. [23,27] Despite a great process, several challenges still remain. For example, salt or gas-phase templates are simple and scalable, but always create large-size pores, giving rise to the severe decrease of the volumetric capacitance. [28] The nanosized solid-phase templates can lead to small-size pores, but are hindered by high cost and the probability of contamination from the removal process. [29] Therefore, the development of a scalable and green template strategy for the synthesis of carbons with rich nanosized porosity is important. Notably, in contrast to the success of solid-and gas-phase templates, liquid-state templates are rarely reported so far, which might be Template-assistant design and fabrication of porous carbon electrode materials has experienced great progress throughout the past decades and yielded lots of successes via various gas or solid state templates. Nevertheless, liquid-state templates are rather rare in preparing porous carbon materials to date. In this work, melting B 2 O 3 beads are used as both templates and a B dopant, leading to unique B, N co-doping hierarchically porous carbons containing a "bubble pool"-like skeleton built of interconnected carbon nanobubbles. Notably, an interesting amending effect of doped B atoms on the N-doped carbon network can be identified for the first time, which creates a "paddy field"-like hybrid microstructure wi...

The large volume expansion induced by K+ intercalation is always a big challenge for designing high‐performance electrode materials in potassium‐ion storage system. Based on the idea that large‐sized ions should accommodate big “houses,” a facile‐induced growth strategy is proposed to achieve the self‐loading of MoS2 clusters inside a hollow tubular carbon skeleton (HTCS). Meantime, a step‐by‐step intercalation technology is employed to tune the interlayer distance and the layer number of MoS2. Based on the above, the ED‐MoS2@CT hybrids are achieved by self‐loading and anchoring the well‐dispersed ultrathin MoS2 nanosheets on the inner surface of HTCSs. This unique compositing model not only alleviates the mechanical strain efficiently, but also provides spacious “roads” (hollow tubular carbon skeleton) and “houses” (interlayer expanded ultrathin MoS2 sheets) for fast K+ transition and storage. As an anode of potassium‐ion batteries, the resultant ED‐MoS2@CT electrode delivers a high specific capacity of 148.5 mAh g−1 at 2 A g−1 after 10 000 cycles with only 0.002% fading per cycle. The assembled ED‐MoS2@CT//PC potassium‐ion hybrid supercapacitor device shows a high energy density of 148 Wh kg−1 at a power density of 965 W kg−1, which is comparable to that of lithium‐ion hybrid supercapacitors.

We demonstrate the design of 2D nanostructured carbon and MnO/carbon electrodes from low-cost biomass-kapok fiber for Li-ion capacitors.

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