B-site Doping Boosts the OER and ORR Performance of Double Perovskite Oxide as Air Cathode for Zinc-Air Batteries.

Double perovskite oxides are key players as electrocatalytic oxygen catalysts in alkaline media. In this study, we synthesized B-site doped NdBaCoaFe2-aO5+δ (a= 1.0, 1.4, 1.6, 1.8) electrocatalysts, systematically to probe their bifunctionality and assess their performance in zinc-air batteries as air cathodes. X-ray photoelectron spectroscopy analysis reveals a correlation between iron reduction and increased oxygen vacancy content, influencing electrocatalyst bifunctionality by lowering the work function. The electrocatalyst with highest cobalt content, NdBaCo1.8Fe0.2O5+δ exhibited a bifunctional index of 0.95 V, outperforming other synthesized electrocatalysts. Remarkably, NdBaCo1.8Fe0.2O5+δ, demonstrated facilitated charge transfer rate in oxygen evolution reaction with four-electron oxygen reduction reaction process. As an air cathode in a zinc-air battery, NdBaCo1.8Fe0.2O5+δ demonstrated superior performance characteristics, including maximum capacity of 428.27 mA h at 10 mA cm-2 discharge current density, highest peak power density of 64 mW cm-2, with an outstanding durability and stability. It exhibits lowest voltage gap change between charge and discharge even after 350 hours of cyclic operation with a rate capability of 87.14%.

Synthesis of N-Doped Graphene Photo-Catalyst for Photo-Assisted Charging of Li-Ion Oxygen Battery.

In this work, nitrogen (N)-doped graphene film is synthesized, as a photo-catalyst, on one side of the copper foam by chemical vapor deposition and the copper foam is directly used as an electrode after porous Pd@rGO cathode loading to the other side of the foam for the photo-assisted charging of the Li-ion oxygen battery. The amount of urea (CO(NH2)2), which is used as N atom source, is optimized to get maximum photo-anodic currents from the n-type graphene films. The optical band gap and the valance band edge potential of the optimized N-doped graphene film are determined as 2.00 eV and 3.71 VLi+/Li, respectively. X-ray photoelectron spectra provided that the atomic percent of N atoms in the graphene film is 1.34% and the graphitic, pyrrolic and pyridinic N atom percentages are 54.01%, 42.20% and 3.79%, respectively. The photo-assisted charging tests indicated that the N-doped graphene film photo-catalyst reduced the charging potential significantly even at 1000 mA g-1 (0.1 mA cm-2) current density and improved the cyclic discharge-charge performance of the Li-ion oxygen battery considerably.

Engineering Oxygen Vacancies in (FeCrCoMnZn)3O4-δ High Entropy Spinel Oxides Through Altering Fabrication Atmosphere for High-Performance Rechargeable Zinc-Air Batteries.

High entropy oxides (HEOs) offer great potential as catalysts for oxygen electrocatalytic reactions in alkaline environments. Herein, a novel synthesis approach to prepare (FeCrCoMnZn)3O4-δ high entropy spinel oxide in a vacuum atmosphere, with the primary objective of introducing oxygen vacancies into the crystal structure, is presented. As compared to the air-synthesized counterpart, the (FeCrCoMnZn)3O4-δ with abundant oxygen vacancies demonstrates a low (better) bifunctional (BI) index of 0.89 V in alkaline media, indicating enhanced electrocatalytic oxygen catalytic activity. Importantly, (FeCrCoMnZn)3O4-δ demonstrates outstanding long-term electrochemical and structural stability. When utilized as electrocatalysts in the air cathode of Zn-air batteries, the vacuum atmosphere synthesized (FeCrCoMnZn)3O4-δ catalysts outperform the samples treated in an air atmosphere, displaying superior peak power density, specific capacity, and cycling stability. These findings provide compelling evidence that manipulating the synthesis atmosphere of multi-component oxides can serve as a novel approach to tailor their electrochemical performance.

Photocatalytic Efficiency of g-C3N4/Graphene Nanocomposites in the Photo-Assisted Charging of the Li-Ion Oxygen Battery.

In this work, we aimed to synthesize an effective nanocomposite photocatalyst for the photo-assisted charging of the Li-ion oxygen battery. Initially the graphene films were synthesized by chemical vapor deposition, and subsequently, g-C3N4/graphene nanocomposites were synthesized by thermal reduction as photocatalysts. FTIR spectra analysis showed that novel C=C bonds can form between g-C3N4 and graphene films during the synthesis process. The photocurrent measurements indicated that the presence of graphene considerably contributed to the visible light utilization and photocatalytic efficiency of g-C3N4. This contribution was also revealed by the UV-vis diffuse reflectance spectra measurements, which showed that the incremental addition of the graphene reduced the optical band gap of the nanocomposite incrementally. The photocatalyst performance of the g-C3N4/graphene nanocomposite was also observed in the photo-assisted charging tests of the Li-ion oxygen battery, and the presence of 2D graphene in the structure improved the effectiveness of g-C3N4 in the reduction of the charging potential, especially at high current densities.

Ultrasound-assisted synthesis of rGO/SiO2-based nanosheets and their electrochemical performances in Li-ion batteries.

In this study, a facile approach has been developed to fabricate GO/SiO2 nanosheets by the hydrolysis of tetraethyl orthosilicate (TEOS) in the graphene oxide (GO) solution with the assistance of the ultrasonication. The morphology and structure of the SiO2/GO nanosheets were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopy. The results showed that the covalently bonded SiO2 nanoparticles onto the GO sheets were dense and uniform. The agglomeration of the nanosheets was prevented by the ultrasonication and the layer sizes decreased throughout the synthesis process. The size and thickness of the SiO2 nanoparticles were determined by the initially and externally added TEOS amounts, respectively, on the GO surface. The anode performance of the thermally reduced rGO/SiO2 nanosheets was also observed in the Li-ion half-cell. The reversible capacity of the synthesized TrGOSN-1.5 anode was 424 mA h g-1 at a current density of 100 mA g-1.

Facile Synthesis and Origin of Enhanced Electrochemical Oxygen Evolution Reaction Performance of 2H-Hexagonal Ba2CoMnO6-δ as a New Member in Double Perovskite Oxides.

Perovskite oxides have been considered promising oxygen evolution reaction (OER) electrocatalysts due to their high intrinsic activity. Yet, their poor long-term electrochemical and structural stability is still controversial. In this work, we apply an A-site management strategy to tune the activity and stability of a new hexagonal double perovskite oxide. We synthesized the previously inaccessible 2H-Ba2CoMnO6-δ (BCM) perovskite oxide via the universal sol-gel method followed by a novel air-quench method. The new 2H-BCM perovskite oxide exhibits outstanding OER activity with an overpotential of 288 mV at 10 mA cm-2 and excellent long-term stability without segregation or structural change. To understand the origin of outstanding OER performance of BCM, we substitute divalent Ba with trivalent La at the A-site and investigate crystal and electronic structure change. Fermi level and valence band analysis presents a decline in the work function with the Ba amount, suggesting a structure-oxygen vacancy-work function-activity relationship for Ba x La2-x CoMnO6-δ (x = 0, 0.5, 1, 1.5, 2) electrocatalysts. Our work suggests a novel production strategy to explore the single-phase new structures and develop enhanced OER catalysts.

Photoassisted Charging of Li-Ion Oxygen Batteries Using g-C3N4/rGO Nanocomposite Photocatalysts.

In this work, g-C3N4/rGO nanocomposites were synthesized to use them as photocatalysts in Li-ion oxygen batteries by aiming at the reduction of the charging potential efficiently under photoassisted conditions. Fourier transform infrared (FTIR) spectra showed that novel C═C bonds formed between g-C3N4 and rGO during the decomposition of melamine and that the formation of these bonds was assumed to cause a red shift in the optical absorption band edge. The competition between the narrowing in the optical band gaps of the nanocomposites as a result of the red shift due to the presence of rGO and the degradation in the visible light utilization as a result of favorably absorbed incident light by rGO instead of g-C3N4 pointed out that the g-C3N4/3% rGO nanocomposite has the optimum light absorbance efficiency. The photoassisted charging tests indicated that the g-C3N4/3% rGO nanocomposite reduced the charging potential effectively, especially at higher current densities, and improved the cyclic discharge-charge performance of the Li-ion oxygen batteries considerably.

Electrochemical Performance of (MgCoNiZn)1-xLixO High-Entropy Oxides in Lithium-Ion Batteries.

High-entropy oxides (HEOs), which are a new class of single-phase solid solution materials, have recently attracted significant attention as an anode material for lithium-ion batteries (LIBs). In this study, (MgCoNiZn)1-xLixO (x = 0.05, 0.15, 0.25, and 0.35) HEOs were synthesized and their electrochemical performances as the anode material were observed in LIBs. X-ray photoelectron spectroscopy (XPS) analysis showed that the increase in the lithium cation concentration causes generation of more oxygen vacancies, which greatly affected the electrochemical performance of (MgCoNiZn)1-xLixO HEO anodes, in the structure. The more the oxygen vacancy concentration in the anode, the higher the discharge capacity in the LIB. The (MgCoNiZn)0.65Li0.35O anode had 1930 mA h g-1 initial and 610 mA h g-1 stable (after 130 cycles) discharge capacities at a current density of 1000 mA g-1. This work clearly indicated that designing a HEO with abundant oxygen vacancies in the structure was a very efficient strategy to improve the electrochemical performance of the HEO electrode for LIBs.