Acacia Senegal–Inspired Bifunctional Binder for Longevity of Lithium–Sulfur Batteries

The sulfur cathode in traditional lithium–sulfur batteries suffers from poor cyclability due to polysulfide shuttling effect as well as large volume change during charge/discharge processes. Gum arabic (GA), a low cost, nontoxic, and sustainable natural polymer from Acacia senegal, is adopted as a binder for the sulfur cathode to address these issues. The excellent mechanical properties of GA endow the cathode with high binding strength and suitable ductility to buffer volume change, while the functional groups chemically and physically confine sulfur species within the cathode to inhibit the shuttling effect of polysulfides. Additionally, GA shifts the electrode fabrication process from the organic solvent process to an aqueous process, eliminates the use of toxic organic solvents, and achieves uniformly distributed electrode with lower impedance. A remarkable cycling performance, i.e., 841 mAh g^?1 at low current rate of C/5, is achieved throughout 500 cycles due to the bifunctions of the GA binder.     

Rice Bifunctional α-Amylase/Subtilisin Inhibitor: Cloning and Characterization of the Recombinant Inhibitor Expressed in Escherichia coli

The complete nucleotide sequences of the cDNA and its gene that encode a bifunctional α-amylase/subtilisin inhibitor of rice (Oryza sativa L.) (RASI) were analyzed. RASI cDNA (939 bp) encoded a 200-residue polypeptide with a molecular mass of 21,417 Da, including a signal peptide of 22 amino acids. Sequence comparison and phylogenetic analysis showed that RASI is closely related to α-amylase/subtilisin inhibitors from barley and wheat. RASI was found to be expressed only in seeds, suggesting that it has a seed-specific function. A coding region of RASI cDNA without the signal peptide was introduced into Escherichia coli and was expressed as a His-tagged protein. Recombinant RASI was purified to homogeneity in a single step by Ni-chelating affinity column chromatography and characterized to elucidate the target enzyme. The recombinant inhibitor had strong inhibitory activity toward subtilisin, with an equimolar relationship, comparable with that of native RASI, and weak inhibitory activity toward some microbial α-amylases, but not toward animal or insect α-amylases. These results suggest that RASI might function in the defense of the seed against microorganisms.     

In Situ Exfoliating and Generating Active Sites on Graphene Nanosheets Strongly Coupled with Carbon Fiber toward Self‐Standing Bifunctional Cathode for Rechargeable Zn–Air Batteries

The self‐standing electrode nanomaterials with highly effective bifunctional electrocatalysis for oxygen reduction and evolution reactions (ORR/OER) are important for practical applications in metal–air batteries. Herein, a defect‐enriched and pyridinic‐N (PN) dominated bifunctional electrocatalyst with novel core–shell architecture (DN‐CP@G) is successfully fabricated by in situ exfoliating graphene from carbon paper followed by high temperature ammonia treatment. Benefitting from its strongly coupled core–shell structure, abundant defective sites and high‐content PN dopants, the DN‐CP@G displays an excellent electrocatalytic (ORR and OER) activity and stability in alkaline media, which are comparable to commercial Pt/C and Ir/C catalysts. The experiment, and theoretical calculations demonstrate that the electrocatalytic activities of carbon materials strongly depend on their defective sites and PN dopants. By directly using DN‐CP@G as a self‐standing electrode, the assembled zinc–air battery demonstrates a high discharge performance and outstanding long‐term cycle stability with at least 250 cycles, which is much superior to the mixed Pt/C and Ir/C electrodes. Remarkably, the DN‐CP@G based all‐solid‐state battery also reveals a good discharge and cycle performance. A facile and cost‐efficient approach to prepare highly effective bifunctional self‐standing electrode is provided by in situ generation of active sites on carbon support for metal–air batteries.     

Low Band Gap Benzimidazole COF Supported Ni3N as Highly Active OER Catalyst

Covalent organic frameworks (COFs) have structures and morphologies closely resembling graphenes, whose modular construction permits atomic‐level manipulations. This, combined with their porous structure, makes them excellent catalyst supports. Here, the high electrocatalytic activity of a composite, formed by supporting Ni₃N nanoparticles on a benzimidazole COF, for oxygen evolution reaction is shown. The composite oxidizes alkaline water with a near‐record low overpotential of 230 mV @ 10 mA cm^?2 (η ₁₀). This high activity is attributed to the ability of the COF to confine the Ni₃N nanoparticles to size regimes otherwise difficult to obtain and to its low band gap character (1.49 eV) arising from the synergy between the conducting Ni₃N nanoparticles and the π‐conjugated COF. The COF itself, as a metal‐free self‐standing framework, has an oxygen evolution reaction activity with η ₁₀ of 400 mV. The periodic structure of the COF makes it serve as a matrix to disperse the catalytically active Ni₃N nanoparticles favoring their high accessibility and thereby good charge‐transport within the composite. This is evident from the amount of O₂ evolved (230 mmol h^?1 g^?1), which, to the best of our knowledge, is the highest reported. The work reveals the emergence of COF as supports for electrocatalysts.     

All‐Solid‐State,Foldable, and Rechargeable Zn‐Air Batteries Based on Manganese Oxide Grown on Graphene‐Coated Carbon Cloth Air Cathode

Pliable, safe, and inexpensive energy storage devices are in demand to power modern flexible electronics. In this work, a foldable battery based on a solid‐state and rechargeable Zn‐air battery is introduced. The air cathode is prepared by coating graphene flakes on pretreated carbon cloth to form a dense, interconnected, and conducting carbon network. Manganese oxide hierarchical nanostructures are subsequently grown on the large surface area carbon network, leading to high loading of active catalyst per unit volume while maintaining the mechanical and electrical integrity of the air cathode. Solid‐state and rechargeable Zn‐air battery with such air cathode exhibits similar polarization curve and resistance at its flat and folded states. The folded battery is able to deliver a power density as high as ≈32 mW cm^?2 and good cycling stability of up to 110 cycles. In addition, the flat battery shows similar discharge/charge curve and stable cycling performance after 100 times of repeated folding and unfolding, indicating its high mechanical robustness.     

Orientation changes of the myosin light chain domain during filament sliding in active and rigor muscle

Structural changes in myosin power many types of cell motility including muscle contraction. Tilting of the myosin light chain domain (LCD) seems to be the final step in transducing the energy of ATP hydrolysis, amplifying small structural changes near the ATP binding site into nanometer-scale motions of the filaments. Here we used polarized fluorescence measurements from bifunctional rhodamine probes attached at known orientations in the LCD to describe the distribution of orientations of the LCD in active contraction and rigor. We applied rapid length steps to perturb the orientations of the population of myosin heads that are attached to actin, and thereby characterized the motions of these force-bearing myosin heads. During active contraction, this population is a small fraction of the total. When the filaments slide in the shortening direction in active contraction, the long axis of LCD tilts towards its nucleotide-free orientation with no significant twisting around this axis. In contrast, filament sliding in rigor produces coordinated tilting and twisting motions.     

Electroless Plating of Highly Efficient Bifunctional Boride‐Based Electrodes toward Practical Overall Water Splitting

Exploring highly‐efficient and low‐cost electrodes for both hydrogen and oxygen evolution reaction (HER and OER) is of primary importance to economical water splitting. Herein, a series of novel and robust bifunctional boride‐based electrodes are successfully fabricated using a versatile Et₂NHBH₃‐involved electroless plating (EP) approach via deposition of nonprecious boride‐based catalysts on various substrates. Owing to the unique binder‐free porous nodule structure induced by the hydrogen release EP reaction, most of the nonprecious boride‐based electrodes are highly efficient for overall water splitting. As a distinctive example, the Co‐B/Ni electrode can afford 10 mA cm^?2 at overpotentials of only 70 mV for HER and 140 mV for OER, and can also survive at large current density of 1000 mA cm^?2 for over 20 h without performance degradation in 1.0 m KOH. Several boride‐based two‐electrode electrolyzers can achieve 10 mA cm^?2 at low voltages of around 1.4 V. Moreover, the facile EP approach is economically viable for flexible and large size electrode production.