Electrocatalytic CO2 reduction to formate by a cobalt phosphino-thiolate complex.

Electrochemical conversion of CO2 to value-added products serves as an attractive method to store renewable energy as energy-dense fuels. Selectivity in this type of conversion can be limited, often leading to the formation of side products such as H2. The activity of a cobalt phosphino-thiolate complex ([Co(triphos)(bdt)]+) towards the selective reduction of CO2 to formate is explored in this report. In the presence of H2O, selective production of formate (as high as 94%) is observed at overpotentials of 750 mV, displaying negligible current degradation during long-term electrolysis experiments ranging as long as 24 hours. Chemical reduction studies of [Co(triphos)(bdt)]+ indicates deligation of the apical phosphine moiety is likely before catalysis. Computational and experimental results suggest a metal-hydride pathway, indicating an ECEC based mechanism.

Interlayer Confined Water Enabled Pseudocapacitive Sodium-Ion Storage in Nonaqueous Electrolyte.

Electrochemical capacitors have faced the limitations of low energy density for decades, owing to the low capacity of electric double-layer capacitance (EDLC)-type positive electrodes. In this work, we reveal the functions of interlayer confined water in iron vanadate (FeV3O8.7·nH2O) for sodium-ion storage in nonaqueous electrolyte. Using an electrochemical quartz crystal microbalance, in situ Raman, and ex situ X-ray diffraction and X-ray photoelectron spectroscopy, we demonstrate that both nonfaradaic (surficial EDLC) and faradaic (pseudocapacitance-dominated Na+ intercalation) processes are involved in the charge storages. The interlayer confined water is able to accelerate the fast Na+ intercalations and is highly stable (without the removal of water or co-intercalation of [Na-diglyme]+) in the nonaqueous environment. Furthermore, coupling the pseudocapacitive FeV3O8.7·nH2O with EDLC-type activated carbon (FeVO-AC) as the positive electrode brings comprehensive enhancements, displaying the enlarged compaction density of ∼2 times, specific capacity of ∼1.5 times, and volumetric capacity of ∼3 times compared to the AC electrode. Furthermore, the as-assembled hybrid sodium-ion capacitor, consisting of an FeVO-AC positive electrode and a mesocarbon microbeads negative electrode, shows a high energy density of 108 Wh kg-1 at 108 W kg-1 and 15.3 Wh kg-1 at 8.3 kW kg-1. Our results offer an emerging route for improving both specific and volumetric energy densities of electrochemical capacitors.

Silicon Cutting Waste Derived Silicon Nanosheets with Adjustable Native SiO2 Shell for Highly-Stable Lithiation/Delithiation.

Silicon is an excellent candidate for the next generation of ultra-high performance anode materials, with the rapid iteration of the lithium-ion battery industry. High-quality silicon sources are the cornerstone of the development of silicon anodes, and silicon cutting waste (SCW) is one of them while still faces the problems of poor performance and unclear structure-activity relationship. Herein, a simple, efficient, and inexpensive purification method is implemented to reduce impurities in SCW and expose the morphology of nanosheets therein. Furthermore, HF is used to modulate the abundant native O in SCW after thermodynamic and kinetic considerations, realizing the mechanical support for the internal Si in the form of an amorphous SiO2 shell. Afterward, SCNS@SiO2 -2.5 with a 1.0 nm thick SiO2 shell exhibits a reversible capacity of 1583.3 mAh g-1 after 200 cycles at 0.8 A g-1 . Ultimately, the molecular dynamics simulations profoundly reveal that the amorphous SiO2 shell is transformed into the extremely ductile Lix SiOy shell to ditch stress and relieve strain during the lithiation/delithiation process.

Manipulating Uniform Nucleation to Achieve Dendrite-Free Zn Anodes for Aqueous Zn-Ion Batteries.

The essence of Zn dendrite formation is ultimately derived from Zn nucleation and growth during the repeated Zn plating/stripping process. Here, the nucleation process of Zn has been analyzed using ex situ scanning electron microscopy to explore the formation of the initial Zn dendrite, demonstrating that the formation of tiny protrusions (the initial state of Zn dendrites) is caused by the inhomogeneity of Zn nucleation. Based on this, the uniform Zn nucleation is promoted by the Ni5Zn21 alloy coating (ZnNi) on the surface of Zn foil by electrodeposition, and the mechanism of ZnNi-promoted even nucleation is further analyzed with the assistance of density functional theory (DFT). The DFT results indicate that the ZnNi displays a stronger binding ability to Zn compared to the bare Zn, suggesting that Zn nuclei will preferentially form around ZnNi instead of continuing to grow on the surface of the initial Zn nuclei. Therefore, the designed Zn metal anode (Zn@ZnNi) can be ultra-stable for over 2200 h at a current density of 2 mA cm-2 in the symmetric cell. Even at a much higher current density of 20 mA cm-2, the extra-long life of over 2200 cycles (over 530 h) can be achieved. Moreover, the full cell with the Zn@ZnNi anode exhibits extra-long cycling performance for 500 cycles with a capacity of 207.7 mA h g-1 and 1100 cycles (148.5 mA h g-1) at a current density of 0.5 and 1 A g-1, respectively.