3D-Printed Zn-Ion Hybrid Capacitor Enabled by Universal Divalent Cation-Gelated Additive-Free Ti3C2 MXene Ink.

The construction of aqueous Zn-ion hybrid capacitors (ZICs) reconciling high energy/power density is practically meaningful yet remains a grand challenge. Herein, a high-capacitance and long-life ZIC is demonstrated by 3D printing of a Ti3C2 MXene cathode, affording optimized carrier transport, facile electrolyte penetration, and ample porosity. The 3D-printable additive-free MXene ink with desirable rheological property is derived by a fast gelation process employing a trace amount of divalent cations, which overcomes the tedious post-treatments required for additive removal. The thus-fabricated 3D-printed (3DP) MXene cathode results in a dual-ion storage mechanism to synergize pseudocapacitive behavior of H+ and electrical double-layer capacitive behavior of Zn2+, which is systematically probed by a wide suite of in situ/ex situ electroanalytic characterizations. The 3DP MXene cathode accordingly exhibits a favorable areal capacitance of 1006.4 mF cm-2 at 0.38 mA cm-2 and excellent rate capability (184.4 F g-1 at 10 A g-1), outperforming the state-of-the-art ZICs. More impressively, ZIC full cells comprising a 3DP MXene cathode and a 3DP Zn anode deliver a competitive energy/power density of 0.10 mWh cm-2/5.90 mW cm-2 as well as an ultralong lifespan (86.5% capacity retention over 6000 cycles at 10 mA cm-2).

Assembly of Nanofluidic MXene Fibers with Enhanced Ionic Transport and Capacitive Charge Storage by Flake Orientation.

MXenes are an emerging class of highly conductive two-dimensional (2D) materials with electrochemical storage features. Oriented macroscopic Ti3C2Tx fibers can be fabricated from a colloidal 2D nematic phase dispersion. The layered conductive Ti3C2Tx fibers are ideal candidates for constructing high-speed ionic transport channels to enhance the electrochemical capacitive charge storage performance. In this work, we assemble Ti3C2Tx fibers with a high degree of flake orientation by a wet spinning process with controlled spinning speeds and morphology of the spinneret. In addition to the effects of cross-linking of magnesium ions between Ti3C2Tx flakes, the electronic conductivity and mechanical strength of the as-prepared fibers have been improved to 7200 S cm-1 and 118 MPa, respectively. The oriented Ti3C2Tx fibers present a volumetric capacitive charge storage capability of up to 1360 F cm-3 even in a Mg-ion based neutral electrolyte, with contributions from both nanofluidic ion transport and Mg-ion intercalation pseudocapacitance. The oriented 2D Ti3C2Tx driven nanofluidic channels with great electronic conductivity and mechanical strength endows the MXene fibers with attributes for serving as conductive ionic cables and active materials for fiber-type capacitive electrochemical energy storage, biosensors, and potentially biocompatible fibrillar tissues.

3D Printing of a V8 C7 -VO2 Bifunctional Scaffold as an Effective Polysulfide Immobilizer and Lithium Stabilizer for Li-S Batteries.

Lithium-sulfur (Li-S) batteries have heretofore attracted tremendous interest due to low cost and high energy density. In this realm, both the severe shuttling of polysulfide and the uncontrollable growth of dendritic lithium have greatly hindered their commercial viability. Recent years have witnessed the rapid development of rational approaches to simultaneously regulate polysulfide behaviors and restrain lithium dendritic growth. Nevertheless, the major obstacles for high-performance Li-S batteries still lie in little knowledge of bifunctional material candidates and inadequate explorations of advanced technologies for customizable devices. Herein, a "two-in-one" strategy is put forward to elaborate V8 C7 -VO2 heterostructure scaffolds via the 3D printing (3DP) technique as dual-effective polysulfide immobilizer and lithium dendrite inhibitor for Li-S batteries. A thus-derived 3DP-V8 C7 -VO2 /S electrode demostrates excellent rate capability (643.5 mAh g-1 at 6.0 C) and favorable cycling stability (a capacity decay of 0.061% per cycle at 4.0 C after 900 cycles). Importantly, the integrated Li-S battery harnessing both 3DP hosts realizes high areal capacity under high sulfur loadings (7.36 mAh cm-2 at a sulfur loading of 9.2 mg cm-2 ). This work offers insight into solving the concurrent challenges for both S cathode and Li anode throughout 3DP.

Universal in Situ Crafted MOx-MXene Heterostructures as Heavy and Multifunctional Hosts for 3D-Printed Li-S Batteries.

The Li-S battery has emerged as a promising next-generation system for advanced energy storage. Notwithstanding the recent progress, the problematic polysulfide shuttling, retarded sulfur redox, and low output of volumetric capacity remain daunting challenges toward its practicability. In response, this work demonstrates herein a universal approach to in situ craft MOx-MXene (M: Ti, V, and Nb) heterostructures as heavy and multifunctional hosts to harvest good battery performances with synchronous polysulfide immobilization and conversion. Theoretical calculations indicate that the in situ implanted oxides boost the reaction kinetics of polysulfide transformation without affecting the intrinsic conductivity of MXene. As a result, the representative VOx-V2C/S electrode enables a high volumetric capacity (offering 1645.98 mAh cm-3 at 0.2 C) and cycling stability (retaining 631.17 mAh cm-3 after 1500 cycles at 2.0 C with a capacity decay of 0.03% per cycle). More encouragingly, 3D-printed sulfur electrodes harnessing VOx-V2C hosts readily harvest an areal capacity of 9.74 mAh cm-2 at 0.05 C under an elevated sulfur loading of 10.78 mg cm-2, holding promise for the development of practically viable Li-S batteries.

Vacuum-assisted black liquor-recycling enhances the sugar yield of sugarcane bagasse and decreases water and alkali consumption.

Black liquor (BL) remains a critical problem during alkaline pretreatment. To solve this issue, a novel pretreatment strategy termed vacuum-assisted black liquor-recycling pretreatment, was established to pretreat sugarcane bagasse (SCB). Firstly, SCB was pretreated with 2% NaOH at 121 °C for 1 h under vacuum conditions. The produced BL was used for subsequent pretreatments after pH recovery with NaOH. The pretreated SCBs were subject to enzymatic hydrolysis and separate hydrolyzation and fermentation (SHF) without washing to neutral pH. BL was recycled on seven occasions. The results indicated that glucose yields did not significantly differ between pretreatment with NaOH and recovered BL. The enzymatic hydrolysis and the fermentation resulted in maximum 0.35 g/g of glucose yield and 116.5 g/kg of ethanol yield respectively. Compared with conventional pretreatment with NaOH, the VABLR method showed high conversion rates of cellulose into monosaccharaides, whilst preserving ~20% and ~46% of alkali and water usage, respectively.

3D Printing of Porous Nitrogen-Doped Ti3C2 MXene Scaffolds for High-Performance Sodium-Ion Hybrid Capacitors.

3D printing technology has stimulated a burgeoning interest to fabricate customized architectures in a facile and scalable manner targeting wide ranged energy storage applications. Nevertheless, 3D-printed hybrid capacitor devices synergizing favorable energy/power density have not yet been explored thus far. Herein, we demonstrate a 3D-printed sodium-ion hybrid capacitor (SIC) based on nitrogen-doped MXene (N-Ti3C2Tx) anode and activated carbon cathode. N-Ti3C2Tx affording a well-defined porous structure and uniform nitrogen doping can be obtained via a sacrificial template method. Thus-formulated ink can be directly printed to form electrode architecture without the request of a conventional current collector. The 3D-printed SICs, with a large areal mass loading up to 15.2 mg cm-2, can harvest an areal energy/power density of 1.18 mWh cm-2/40.15 mW cm-2, outperforming the state-of-the-art 3D-printed energy storage devices. Furthermore, our SIC also achieves a gravimetric energy/power density of 101.6 Wh kg-1/3269 W kg-1. This work demonstrates that the 3D printing technology is versatile enough to construct emerging energy storage systems reconciling high energy and power density.

Pre-treatment of sugarcane bagasse with aqueous ammonia-glycerol mixtures to enhance enzymatic saccharification and recovery of ammonia.

In this work, an efficient aqueous ammonia with glycerol (AAWG) method to improve the digestibility of sugarcane bagasse (SCB) was developed. Response surface methodology was utilized to optimize the AAWG parameters to achieve the maximum total fermentable sugar concentration (TFSC) and total fermentable sugar yield (TFSY). Under optimal AAWG conditions, 13.59 g/L TFSC (9.25% ammonia, 1.86 h, 180 °C) and 0.4449 g/g TFSY (9.51% ammonia, 1.78 h, 180 °C) were achieved, with delignification of 77.81% and 70.91%, respectively. Compared to pretreatment with glycerol or aqueous ammonia, the AAWG method significantly enhanced the enzymatic efficiency of SCB. The ammonia was recovered from the pretreatment liquid by distillation, and about one-third of the ammonia was retained. The overall results indicate that AAWG is effectively used as a pretreatment method for recovering ammonia, which would largely contribute to the economic benefits of biomass biorefinery.