Dual-Scale Integration Design of Sn-ZnO Catalyst toward Efficient and Stable CO2 Electroreduction.

Electrochemical CO2 reduction to CO is a potential sustainable strategy for alleviating CO2 emission and producing valuable fuels. In the quest to resolve its current problems of low-energy efficiency and insufficient durability, a dual-scale design strategy is proposed by implanting a non-noble active Sn-ZnO heterointerface inside the nanopores of high-surface-area carbon nanospheres (Sn-ZnO@HC). The metal d-bandwidth tuning of Sn and ZnO alters the extent of substrate-molecule orbital mixing, facilitating the breaking of the *COOH intermediate and the yield of CO. Furthermore, the confinement effect of tailored nanopores results in a beneficial pH distribution in the local environment around the Sn-ZnO nanoparticles and protects them against leaching and aggregating. Through integrating electronic and nanopore-scale control, Sn-ZnO@HC achieves a quite low potential of -0.53 V vs reversible hydrogen electrode (RHE) with 91% Faradaic efficiency for CO and an ultralong stability of 240 h. This work provides proof of concept for the multiscale design of electrocatalysts.

Self-Formation CoO Nanodots Catalyst in Co(TFSI)2 -Modified Electrolyte for High Efficient Li-O2 Batteries.

The major challenges for Li-O2 batteries are sluggish reaction kinetics and large overpotentials due to the cathode passivation resulting from insulative and insoluble Li2 O2 . Here, a novel nanodot (ND)-modified electrolyte is designed by employing cobalt bis(trifluoromethylsulfonyl)imide (Co(TFSI)2 ) as an electrolyte additive. The Co(TFSI)2 additive can react with discharge intermediate LiO2 and product Li2 O2 to form CoO NDs. The generated CoO NDs are well dispersed in electrolyte, which integrates both the high catalytic activity of solid catalyst and the good wettability of soluble catalyst. Under the catalytis of CoO NDs, Li2 O2 is produced and deposits on the cathode together with them. At the recharge process, these well dispersed CoO NDs help to decompose solid Li2 O2 at a lower overpotential. The Li-O2 cells with Co(TFSI)2 exhibit a long cycle life of 200 cycles at a current density of 200 mA g-1 under a cutoff capacity of 1000 mAh g-1 , as well as a superior reversibility associated with the Li2 O2 formation and decomposition. The study is expected to broaden the range of electrolyte additives and provide a new view to developing highly dispersed NDs-based catalysts for Li-O2 batteries.

"Two Ships in a Bottle" Design for Zn-Ag-O Catalyst Enabling Selective and Long-Lasting CO2 Electroreduction.

Electrochemical CO2 reduction (CO2RR) using renewable energy sources represents a sustainable means of producing carbon-neutral fuels. Unfortunately, low energy efficiency, poor product selectivity, and rapid deactivation are among the most intractable challenges of CO2RR electrocatalysts. Here, we strategically propose a "two ships in a bottle" design for ternary Zn-Ag-O catalysts, where ZnO and Ag phases are twinned to constitute an individual ultrafine nanoparticle impregnated inside nanopores of an ultrahigh-surface-area carbon matrix. Bimetallic electron configurations are modulated by constructing a Zn-Ag-O interface, where the electron density reconfiguration arising from electron delocalization enhances the stabilization of the *COOH intermediate favorable for CO production, while promoting CO selectivity and suppressing HCOOH generation by altering the rate-limiting step toward a high thermodynamic barrier for forming HCOO*. Moreover, the pore-constriction mechanism restricts the bimetallic particles to nanosized dimensions with abundant Zn-Ag-O heterointerfaces and exposed active sites, meanwhile prohibiting detachment and agglomeration of nanoparticles during CO2RR for enhanced stability. The designed catalysts realize 60.9% energy efficiency and 94.1 ± 4.0% Faradaic efficiency toward CO, together with a remarkable stability over 6 days. Beyond providing a high-performance CO2RR electrocatalyst, this work presents a promising catalyst-design strategy for efficient energy conversion.

O2 Adsorption Associated with Sulfur Vacancies on MoS2 Microspheres.

MoS2 is well-known for its catalytic properties, mainly to adsorb hydrogenous or carbonaceous materials. However, the effect of MoS2 on the oxygen adsorption has been investigated only a few times thus far. In this work, we first studied the adsorbability of O2 by MoS2 through the analysis of Li2O2 growth on the surface of flower-like MoS2 microspheres with different concentrations of sulfur vacancies, which can be applied as the highly active electrocatalysts for Li-O2 batteries. The enhancement of battery performance for the Def-MoS2@CTs (CTs = carbon textile substrates) with a larger concentration of sulfur vacancies (S/Mo = 1.61) can be achieved. The experimental and theoretical results confirm that the sulfur vacancies play a crucial role in the adsorption process and thus affect the morphology and nucleation of Li2O2. In addition, a fundamental catalytic mechanism for this adsorption process is also proposed. These results provide a new insight into the development of a highly active electrocatalyst by introducing a large concentration of defects for Li-O2 batteries.

Binary Mixtures of Highly Concentrated Tetraglyme and Hydrofluoroether as a Stable and Nonflammable Electrolyte for Li-O2 Batteries.

Developing a long-term stable electrolyte is one of the most enormous challenges for Li-O2 batteries. Equally, the high flammability of frequently used solvents seriously weakens the electrolyte safety in Li-O2 batteries, which inevitably restricts their commercial applications. Here, a binary mixture of highly concentrated tetraglyme electrolyte (HCG4) and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) was used for a novel electrolyte (HCG4/TTE) in Li-O2 batteries, which exhibit good wettability, enhanced ionic conductivity, considerable nonflammability, and high electrochemical stability. Being a co-solvent, TTE can contribute to increasing ionic conductivity and to improving flame retardance of the as-prepared electrolyte. The cell with this novel electrolyte displays an enhanced cycling stability, resulting from the high electrochemical stability during cycling and the formation of electrochemically stable interfaces prevents parasitic reactions occurring on the Li anode. These results presented here demonstrate a novel electrolyte with a high electrochemical stability and considerable safety for Li-O2 batteries.

3D Foam-Like Composites of Mo2C Nanorods Coated by N-Doped Carbon: A Novel Self-Standing and Binder-Free O2 Electrode for Li-O2 Batteries.

The development of self-standing and binder-free O2 electrodes is significant for enhancing the total specific energy density and suppressing parasitic reactions for Li-O2 batteries, which is still a formidable challenge thus far. Here, a three-dimensional foam-like composite composed of Mo2C nanorods decorated by different amounts of N-doped carbon (Mo2C-NR@xNC (x = 5, 11, and 16 wt %)) was directly employed as the O2 electrode without applications of any binders and current collectors. Mo2C-NR@xNC presents a network microstructure with interconnected macropore and mesoporous channels, which is beneficial to achieving fast Li+ migration and O2 diffusion, facilitating the electrolyte impregnation, and providing enough space for Li2O2 storage. Additionally, the coated N-doped carbon layer can largely improve the electrochemical stability and conductivity of Mo2C. The cell with Mo2C-NR@11NC shows a considerable cyclability of 200 cycles with an overpotential of 0.28 V in the first cycle at a constant current density of 100 mA g-1, a superior reversibility associated with the formation and decomposition of Li2O2 as desired, and a high electrochemical stability. On the basis of the experimental results, the electrochemical mechanism for the cell using Mo2C-NR@11NC is proposed. These results represent a promising process in the development of a self-standing and binder-free foam-based electrode for Li-O2 batteries.

Electrospinning of Nanofibers for Energy Applications.

With global concerns about the shortage of fossil fuels and environmental issues, the development of efficient and clean energy storage devices has been drastically accelerated. Nanofibers are used widely for energy storage devices due to their high surface areas and porosities. Electrospinning is a versatile and efficient fabrication method for nanofibers. In this review, we mainly focus on the application of electrospun nanofibers on energy storage, such as lithium batteries, fuel cells, dye-sensitized solar cells and supercapacitors. The structure and properties of nanofibers are also summarized systematically. The special morphology of nanofibers prepared by electrospinning is significant to the functional materials for energy storage.