Ultrahigh‐Loading Zinc Single‐Atom Catalyst for Highly Efficient Oxygen Reduction in Both Acidic and Alkaline Media

Atomically dispersed Zn–N–C nanomaterials are promising platinum‐free catalysts for the oxygen reduction reaction (ORR). However, the fabrication of Zn–N–C catalysts with a high Zn loading remains a formidable challenge owing to the high volatility of the Zn precursor during high‐temperature annealing. Herein, we report that an atomically dispersed Zn–N–C catalyst with an ultrahigh Zn loading of 9.33 wt % could be successfully prepared by simply adopting a very low annealing rate of 1° min^?1. The Zn–N–C catalyst exhibited comparable ORR activity to that of Fe–N–C catalysts, and significantly better ORR stability than Fe–N–C catalysts in both acidic and alkaline media. Further experiments and DFT calculations demonstrated that the Zn–N–C catalyst was less susceptible to protonation than the corresponding Fe–N–C catalyst in an acidic medium. DFT calculations revealed that the Zn–N₄ structure is more electrochemically stable than the Fe–N₄ structure during the ORR process.     

An Electrolytic Zn–MnO2 Battery for High‐Voltage and Scalable Energy Storage

Zinc‐based electrochemistry is attracting significant attention for practical energy storage owing to its uniqueness in terms of low cost and high safety. However, the grid‐scale application is plagued by limited output voltage and inadequate energy density when compared with more conventional Li‐ion batteries. Herein, we propose a latent high‐voltage MnO₂ electrolysis process in a conventional Zn‐ion battery, and report a new electrolytic Zn–MnO₂ system, via enabled proton and electron dynamics, that maximizes the electrolysis process. Compared with other Zn‐based electrochemical devices, this new electrolytic Zn–MnO₂ battery has a record‐high output voltage of 1.95 V and an imposing gravimetric capacity of about 570 mAh g^?1, together with a record energy density of approximately 409 Wh kg^?1 when both anode and cathode active materials are taken into consideration. The cost was conservatively estimated at <US$ 10 per kWh. This result opens a new opportunity for the development of Zn‐based batteries, and should be of immediate benefit for low‐cost practical energy storage and grid‐scale applications.     

Direct Determination of Phosphite in Fertilizers by Flow‐Injection Amperometry

A sensor based on graphite electrode modified with palladium‐platinum‐palladium film is proposed for phosphite determination by flow‐injection amperometry. The modified electrode was prepared by a sequential cathodic deposition of Pd, Pt and Pd on a graphite electrode from 0.5% m/v PdCl₂+28% m/v NH₄OH and 2% m/v H₂PtCl₆+10% v/v H₂SO₄ solutions. After suitable conditioning, the electrode showed catalytic activity for phosphite oxidation when 0.15 V was applied. The proposed system handles approximately 50 samples per hour (0.01–0.05 mol L^?1 Na₂HPO₃; R²=0.9997), consuming ca. 70 μL of sample per determination. The limit of detection and amperometric sensibility were 5×10^?4 mol L^?1 and 1.5 mA L mol^?1, respectively. The proposed method was applied to analysis of fertilizer samples without pre‐treatment. Results are in agreement with those obtained by spectrophotometry and titrimetry at 95% confidence level and good recoveries (96–109%) of spiked samples were found. Relative standard deviation (n= 12) of a 0.01 mol L^?1 Na₂HPO₃ sample was 2%. The useful lifetime of modified electrode was around 220 determinations. For routine purposes it means that this electrode can be continuously used for 5 hours.     

Differences in Dynamics between Crosslinked and Non‐Crosslinked Hyaluronates Measured by using Fast Field‐Cycling Relaxometry

The dynamic properties of water molecules in gels containing linear and crosslinked hyaluronic acid polymers are investigated by using an integrated approach that includes relaxometry, solid‐state NMR spectroscopy, and scanning electron microscopy. A model‐free analysis of field‐dependent nuclear relaxation is applied to obtain information on mobility and the population of different pools of water molecules in the gels. Differences between linear and crosslinked hyaluronic acid polymers are observed, indicating that crosslinking increases both the fraction and the correlation time of water molecules with slow dynamics.     

Real‐Time Intracellular Measurements of ROS and RNS in Living Cells with Single Core–Shell Nanowire Electrodes

Nanoelectrodes allow precise and quantitative measurements of important biological processes at the single living‐cell level in real time. Cylindrical nanowire electrodes (NWEs) required for intracellular measurements create a great challenge for achieving excellent electrochemical and mechanical performances. Herein, we present a facile and robust solution to this problem based on a unique SiC‐core–shell design to produce cylindrical NWEs with superior mechanical toughness provided by the SiC nano‐core and an excellent electrochemical performance provided by the ultrathin carbon shell that can be used as such or platinized. The use of such NWEs for biological applications is illustrated by the first quantitative measurements of ROS/RNS in individual phagolysosomes of living macrophages. As the shell material can be varied to meet any specific detection purpose, this work opens up new opportunities to monitor quantitatively biological functions occurring inside cells and their organelles.     

Controlling Regioselectivity in the Enantioselective N‐Alkylation of Indole Analogues Catalyzed by Dinuclear Zinc‐ProPhenol

The enantioselective N‐alkylation of indole and its derivatives with aldimines is efficiently catalyzed by a zinc‐ProPhenol dinuclear complex under mild conditions to afford N‐alkylated indole derivatives in good yield (up to 86 %) and excellent enantiomeric ratio (up to 99.5:0.5 e.r.). This method tolerates a wide array of indoles, as well as pyrrole and carbazole, to afford the corresponding N‐alkylation products. The reaction can be run on a gram scale with reduced catalyst loading without impacting the efficiency. The chiral aminals were further elaborated into various chiral polyheterocyclic derivatives. The surprising stability of the chiral N‐alkylation products will open new windows for asymmetric catalysis and medicinal chemistry.