Benzoic Acid: Electrode-Regenerated Molecular Catalyst to Boost Cycloolefin Epoxidation.

Stoichiometric oxidants are always consumed in organic oxidation reactions. For example, olefins react with peroxy acids to be converted to epoxy, while the oxidant, peroxy acid, is downgraded to carboxylic acid. In this paper, we aim to regenerate carboxylic acid into peroxy acid through electric water splitting at the anode, in order to construct an electrochemical catalytic cycle to accomplish the cycloolefin epoxidation reaction. Benzoic acid, which can be strongly adsorbed onto the anode and rapidly converted to peroxy acid, was selected to catalyze the cycloolefin epoxidation. Furthermore, the peroxybenzoic acid will be further activated on the electrode to fulfill the epoxidation and release the benzoic acid to complete the catalytic cycle. In this designed reaction cycle, benzoic acid acts as a molecular catalyst with the assistance of the electrode-generated reactive oxygen species (ROS). This method can successfully reform the consumable oxidants to molecular catalysts, which can be generalized to other green organic syntheses.

Stable Lithium-Sulfur Batteries Ensured by GeS2 and α-S8 Lattice Matching During the Charge Process.

The charge process of lithium-sulfur batteries (LSBs) is a process in which molecular polarity decreases and the volume shrinks gradually, which is the process most likely to cause lithium polysulfides (LiPSs) loss and interfacial collapse. In this work, GeS2 is utilized, whose (111) lattice plane exactly matches with the (113) lattice of α-S8 , to solve these problems. GeS2 can regulate the interconversion-deposition behavior of S-species during the charge process. Soluble LiPSs can be spontaneously adsorbed on the GeS2 surface, then obtain electrons and eventually convert to α-S8 molecules. More importantly, the α-S8 molecules will crystallize uniformly along the (111) lattice plane of GeS2 to maintain a stable cathode-electrolyte interface. Therefore, outstanding charge/discharge LSBs are successfully accomplished.

Electrochemical oxidation of styrene to benzaldehyde by discrimination of spin-paired π electrons.

The oxidation of styrene to benzaldehyde has been a considerable challenge in the electrochemical synthesis of organic compounds because styrene is more easily oxidized to benzoic acid. In this work, MnO2 with an asymmetric electronic configuration is designed to discriminate the spin-paired π electrons of styrene. One of these discriminated π electrons combined with reactive oxygen species (ROS), ˙OH, ˙OOH, etc., produced simultaneously on a MnO2/(Ru0.3Ti0.7)O2/Ti bifunctional anode, to form benzaldehyde via Grob fragmentation, rather than benzoic acid. However, only benzoic acid is obtained from the oxidation of styrene on the anodes MOs/(Ru0.3Ti0.7)O2/Ti, where MOs are other metal oxides with symmetric electronic configurations.

Suppress Loss of Polysulfides in Lithium-Sulfur Battery by Regulating the Rate-Determining Step via 1T MoS2-MnO2 Covering Layer.

The commercialization of lithium-sulfur batteries (LSBs) is obstructed by several technical challenges, the most severe of which is the irreversible loss of soluble polysulfide intermediates. These soluble polysulfides must be anchored or confined in the cathode side to maintain the long life of the LSBs. Here, 1T MoS2-MnO2/CC heterostructure functional covering layer is designed to regulate the rate-determining step from the liquid-to-solid reaction to solid-to-solid reaction. Rapid and uniform nucleation of solid Li2S2/Li2S is therefore achieved, and the loss of soluble polysulfides is retarded. The Li-S batteries assembled with 1T MoS2-MnO2/CC covering layer therefore deliver outstanding rate capabilities even under high sulfur loads and large current rates. This study paves a novel way to suppress the polysulfides' "farewell effect" from the perspective of the kinetics.

Nanoarray Architecture of Ultra-Lithiophilic Metal Nitrides for Stable Lithium Metal Anodes.

Lithium metal anode (LMA) is puzzled by the serious issues corresponding to infinite volume change and notorious lithium dendrite during long-term stripping/plating process. Herein, the transition metal nitrides array with outstanding lithiophilicity, including CoN, VN, and Ni3 N, are decorated onto carbon framework as "nests" to uniform Li nucleation and guide Li metal deposition. These transition metal nitrides with excellent conductivity can guarantee the fast electron transport, therefore maintain a stable interface for Li reduction. In addition, the designed multi-dimensional structure of metal nitride array decorated carbon framework can effectively regulate the growth of Li metal during the stripping/plating process. Of note, attributing to the lattice-matching between CoN and Li metal, the composite Li/CoN@CF anode exhibits ultra-stable cycling performance in symmetrical cells (over 4000 h@1 mA cm-2 with 1 mAh cm-2 and 1000h@20 mA cm-2 with 20 mAh cm-2 ). The assembled full cells based on Li/CoN@CF composite anode, LiFePO4 or S as cathodes, deliver excellent cycling stability and rate capability. This strategy provides an effective approach to develop a stable lithium metal anode for lithium metal batteries.

Enhanced catalysis of radical-to-polysulfide interconversion via increased sulfur vacancies in lithium-sulfur batteries.

The practical application of lithium-sulfur (Li-S) batteries is seriously hindered by severe lithium polysulfide (LiPS) shuttling and sluggish electrochemical conversions. Herein, the Co9S8/MoS2 heterojunction as a model cathode host material is employed to discuss the performance improvement strategy and elucidate the catalytic mechanism. The introduction of sulfur vacancies can harmonize the chemisorption of the heterojunction component. Also, sulfur vacancies induce the generation of radicals, which participate in a liquidus disproportionated reaction to reduce the accumulation of liquid LiPSs. To assess the conversion efficiency from liquid LiPSs to solid Li2S, a new descriptor calculated from basic cyclic voltammetry curves, nucleation transformation ratio, is proposed.

3D Net-like GO-d-Ti3C2Tx MXene Aerogels with Catalysis/Adsorption Dual Effects for High-Performance Lithium-Sulfur Batteries.

High theoretical specific capacity and rich resources in nature make sulfur an ideal cathode material for lithium-metal batteries. However, the shuttle effect and sluggish reduction reaction kinetics of lithium polysulfides (LiPSs) seriously affect the performance of the batteries. Here, we report GO-d-Ti3C2Tx MXene aerogels with a novel three-dimensional (3D) reticular structure that served as sulfur host cathode materials for lithium-sulfur batteries (LiSBs), which benefits adsorption/catalytic conversion of LiPSs simultaneously. The dissolved LiPSs can be rapidly captured through chemisorption and then catalyzed into insoluble Li2S by low-coordinated-state Ti on the d-Ti3C2Tx MXene surface. The combination of adsorption and catalysis enormously improves the capacity and cycling performance of LiSBs. At an S mass loading of 1.5 mg cm-2, the cell with the S@GM0.4 composite electrode achieves excellent cycling performance. The discharge specific capacity of 1039 mA h g-1 (1.56 mA h cm-2) decays to 542.9 mA h g-1 after 1000 cycles with a capacity fading rate of 0.048% per cycle at 0.5 C. Even at an S mass loading of 4.88 mg cm-2, an areal capacity of 4.3 mA h cm-2 can be achieved at 0.2 C.

Densely vertical-grown NiFe hydroxide nanosheets on a 3D nickel skeleton as a dendrite-free lithium anode.

Densely vertical-grown NiFe hydroxide nanosheets on a nickel foam (DVS-NFOH@NF) were designed and synthesized for a dendrite-free lithium anode. As a result, the Li dendrite was significantly suppressed. The invented Li anode presented a uniform morphology and great cycle performance in a symmetric cell.

Lattice-matching Ni-based scaffold with a spongy cover for uniform electric field against lithium dendrites.

Herein, carbonized nickel metal organic framework scaffolds at nickel foam (CNS@NF) were fabricated to regulate Li-ion plating/stripping in lithium cells. CNS@NF would contribute to uniform Li nucleation and low overpotential due to the small lattice mismatch ratio and homogenous lithiophilic sites. Moreover, the spongy structure of the carbonized MOF can reduce the local current density by smoothening the sharp edges of NiO. Owing to these advantages, both the symmetric cells and full cells exhibited excellent electrochemical performance.

"Superaerophobic" NiCo bimetallic phosphides for highly efficient hydrogen evolution reaction electrocatalysts.

A "superaerophobic" NiCo bimetallic phosphide electrocatalyst has been fabricated by employing bimetal-organic frameworks as self-sacrificing templates. An overpotential of only 205 mV can drive the HER current density to 800 mA cm-2, which is even superior to that for Pt/C. This study provides a promising approach for the development of industrialized HER electrocatalysts.

Balancing the Seesaw: Investigation of a Separator to Grasp Polysulfides with Diatomic Chemisorption.

Lithium-sulfur (Li-S) batteries are promising next-generation high-density energy storage systems due to their advantages of high theoretical specific capacity, environmental compatibility, and low cost. However, high-order polysulfides dissolve in the electrolyte and subsequently lead to the undesired polysulfide shuttle effect, which hinders the commercialization of Li-S batteries. To tackle this issue, morpholine molecules were successfully grafted onto a commercial polypropylene separator. Density functional theory (DFT) calculations were performed and revealed that morpholine side chains could equally and reversibly grasp all the high-order polysulfides. This diatomic chemisorption adjusted the transformation process among the sulfur-related compounds. The modified separator battery possessed a discharge capacity as high as 827.8 mAh·g-1 after 500 cycles at 0.5 C. The low capacity fading rate, symmetrical cyclic voltammogram, and retention of the electrode morphology all suggest that the diatomic equal adsorption approach can successfully suppress the polysulfide shuttle effect while maintaining excellent battery performance.

Construction of Soft Base Tongs on Separator to Grasp Polysulfides from Shuttling in Lithium-Sulfur Batteries.

Rechargeable lithium-sulfur batteries, which use sulfur as the cathode material, promise great potentials to be the next-generation high-energy system. However, higher-order lithium polysulfides, Li2 Sx (x = 4, 6, and 8), regardless of in charge or in discharge, always form first, dissolve subsequently in the electrolyte, and shuttle to the cathode and the anode, which is called "shuttle effect." The polysulfides shuttle effect leads to heavy loss of the active-sulfur materials. Literature works mostly "cover or fill" the pores to block polysulfides from shuttling, which also hinder the lithium ion transfer. Here a protocol is invented to grasp polysulfides based on the "soft and hard acid-base" theory. Tertiary amine layer (TAL) polymerized on a polypropylene separator selectively coordinates with the dissolved high-order Li2 Sx in the cathode. Meanwhile, the transportation of lithium cations is not interrupted because of enough pores left for their transportation. After 400 cycles of charge/discharge at 0.5C, the TAL modified separator battery still possesses a capacity of 865 mAh g-1 , which is among the best of the state-of-the-art performances of lithium-sulfur batteries. The flexible "polysulfides tongs" construction method paves a new way for Li-S batteries to reach desired performances with less worry about polysulfides shuttle.

Enhanced Conductivity of Anion-Exchange Membrane by Incorporation of Quaternized Cellulose Nanocrystal.

High ion conductivity of anion-exchange membrane is essential for the operation of alkaline anion-exchange membrane fuel cell. In this work, we demonstrated an effective strategy to enhance the conductivity of anion-exchange membrane (AEM), by incorporation of quaternized cellulose nanocrystal (QCNC) for the first time. Morphology observation demonstrated a uniform distribution of QCNC within QPPO matrix, as well as a clear QCNC network, which led to significant enhancement in hydroxide conductivities of composite membranes, for example, 2 wt % QCNC/QPPO membrane possessed a conductivity of 160% (60 mS cm-1, @80 °C) of that of QPPO. Furthermore, H2/O2 cell performance of membrane electrode assembly based on 2 wt % QCNC/QPPO AEM showed an excellent peak power density of 392 mV cm-2 at 60 °C without back pressure, whereas that of neat QPPO AEM was only 270 mV cm-2.