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–x Li x O (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–x Li x O 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.

In this work, g-C 3 N 4 /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-C 3 N 4 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-C 3 N 4 pointed out that the g-C 3 N 4 /3% rGO nanocomposite has the optimum light absorbance efficiency. The photoassisted charging tests indicated that the g-C 3 N 4 /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. KEYWORDS: g-C 3 N 4 /rGO, nanocomposites, photocharging, Li-ion oxygen batteries, photocatalyst

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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.

Summary High‐entropy oxides (HEOs) have gained significant attention from lithium‐ion batteries since they can present cycling stability and possess a high specific capacity. While many studies have focused on discovering new high entropy oxides by changing their components, the influence of the synthesis environment on the structural properties and thus electrochemical behavior remain unresolved. Herein, we studied the effect of the synthesis environment, which is argon and air on the structural and electrochemical properties of (FeMnCrCoZn)3O4 powders. We observed that the synthesis atmosphere affects greatly oxygen vacancy formation. The sample synthesized under an argon atmosphere (HESO‐Ar) shows enhanced cycling and rate performances. Our work can open up new opportunities in designing HEO‐based anodes and utilizing other HEO‐based functional materials by altering and controlling the synthesis environment.