Single-atomic Fe-N₄ is the well-acknowledged active site in iron-nitrogen-carbon (Fe-N-C) material for oxygen reduction reaction (ORR). The adjusting of the electronic distribution of Fe-N₄ is promising for further enhancing the performance of the Fe-N-C catalyst. Herein, a phosphorus (P)-doped Fe-N-C catalyst with penta-coordinated single atom sites (FeNPC) is reported for efficient oxygen reduction. Fe K-edge X-ray absorption spectroscopy (XAS) verifies the coordination environment of single Fe atom, while density functional theory (DFT) calculations reveal that the penta-coordination and neighboring doped P atoms can simultaneously change the electronic distribution of Fe-N₄ and its adsorption strength of key intermediates, reducing the reaction-free energy of the potential-limiting step. Electrochemical tests validate the remarkable intrinsic ORR activity of FeNPC in alkaline media (a half-wave potential (E_1/2) of 0.904 V vs. reversible hydrogen electrode (RHE) and limited current density (J_L) of 6.23 mA·cm⁻²) and an enhanced ORR performance in neutral (E_1/2 = 0.751 V, J_L = 5.27 mA·cm⁻²) and acidic media (E_1/2 = 0.735 V, J_L = 5.82 mA·cm⁻²) with excellent stability, highlighting the benefits of optimizing the local environment of single-atomic Fe-N₄.

Hydrated vanadium oxide (VOH) is a promising cathode candidate for the aqueous zinc-ion batteries (AZIBs), due to the large interlayer spacing and high capacity. However, severe pulverization and structure collapse upon cycling limit its practical application. Herein, preintercalation strategy with higher positive charge of Cr³⁺ is proposed to regulate the structure and oxygen defect of the VOH-O_d. The VOH-O_d with moderated amount of Cr³⁺ incorporation (M-CrVOH-O_d), showing a flower-like hierarchical structure assembled with thin nanosheets, can expand the interlayer spacing and increase the oxygen defect, inducing an enhanced high-rate cycling capability. As a result, M-CrVOH-O_d delivers a high capacity of 405 mAh·g⁻¹ at 0.5 A·g⁻¹, high capacity retention of 120% over 3,500 cycles, as well as an extraordinary energy output (297.3 Wh·kg⁻¹ at 355.9 W·kg⁻¹). The density functional theory (DFT) calculations can prove the enhanced reaction kinetics with narrower bandgap and lower Zn²⁺ adsorption energy after the Cr-preintercalation. Meanwhile, based on the ex-situ X-ray diffraction (XRD) analysis, synergistic intercalation of the Zn²⁺/H⁺ into the interlayers of M-CrVOH-O_d can bring the high specific capacity. This work could help us understand the enhanced performance of VOH from the point of the chemical reactions.

Facile design of economic-effective hydrogen evolution reaction (HER) catalysts with non-noble materials are promising for the production of renewable chemical fuels. Two-dimensional (2D) ultrathin transition metal dichalcogenides (TMDs) materials with large specific surface area and abundant catalytic active sites can significantly enhance their catalytic activities. Herein, we design and synthesize an atomically thin Ni-Se-S based hybrid nanosheet (NiSe_1.2S_0.8) via a simple solvothermal method, the thickness of NiSe_1.2S_0.8 nanosheets is only about 1.1 nm. Benefiting from the ultrathin nanostructure and rich defects, the optimal NiSe_1.2S_0.8 exhibits good electrocatalytic activity with the overpotential of 144 mV at -10 mA·cm^-2, a small Tafel slope of 59 mV·dec^-1, and outstanding catalytic stability in acid electrolyte for HER. The theoretical results show that hybrid electrocatalyst by S incorporation possesses the optimal adsorption free energy of hydrogen (ΔG_H*). This study provides a simple method to synthesize a high-performance multicomponent electrocatalysts with the ultrathin nanostructures and abundant defects.