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Anion exchange membrane fuel cells and water electrolyzers are promising hydrogen energy conversion devices due to more abundant options toward catalysts under alkaline conditions. However, the sluggish hydrogen electrode reaction kinetics remains a major challenge for wide applications. Herein, we conceive atomically dispersed Pt on Ni single-atom/nitrogen-doped carbon (Pt A/C -Ni-NC), in which the Pt co-exists in Pt single atoms (Pt A -N4 sites) and atomically dispersed Pt clusters (Pt C). Such a multi-atom scale Pt A/C -Ni-NC structure greatly enhances the active site density and atomic utilization by balancing hydrogen adsorption energy and hydroxyl adsorption energy, leading to significantly elevated hydrogen oxidation and evolution reactions (HOR/HER) catalysis activity. For HOR, it reaches a current density of 3.75 mA cm−2 at a potential of 200 mV, with a mass activity of 72.3 mA mg−1, which is 3 times higher than that of commercial Pt/C. For HER, to deliver the current density of 10 mA cm−2, the overpotential is only 10 mV, with a mass activity of 2217.7 mA mg−1, which is 8.4 times higher than that of commercial Pt/C. Density functional theory (DFT) calculations and in-situ detection results further confirm that the equilibrium between hydrogen binding energy (HBE) and hydroxyl binding energy (OHBE), and the unique interfacial water on the catalyst surface are responsible for high activity of the catalyst. This work provides important insights into developing multi-atom scale catalysts for efficient hydrogen electrode reactions and deeper understanding active sites dispersed at the atomic level. [Display omitted] • Realizing atomization of Pt, with rich and highly dispersed Pt single atoms (Pt A) and clusters (Pt C) on Ni-NC (Pt A/C -Ni-NC). • DFT calculation and in-situ detection results confirm that atomized Pt equilibrates the adsorption behavior on catalyst. • Hydrogen bonding of atomized Pt interfacial water is weakened, facilitating interfacial water migration and reaction. • Balanced active intermediate adsorption capacity allows Pt A/C -Ni-NC with excellent hydrogen electrode reaction performance. [ABSTRACT FROM AUTHOR]

Fe-based polyanionic materials are potential cathode candidates for sodium-ion batteries, however, voltage decay and cycling stability become main challenges for practical applications. Besides, the mechanism of phase transition during charge/discharge processes is still unclear. Herein, the Fe-rich phase Na 1.4 Fe 1.3 P 2 O 7 with Na/Fe atom vacancies is constructed, showing robust voltage decay suppression and a larger ratio of the plateau length (6:1) at 3.0 and 2.5 V than that of the conventional Na-rich phase Na 2 FeP 2 O 7 (2.5:1). After 650 cycles at 1 C, the capacity and average voltage retentions of Fe-rich phase are 84 % and 95 %, respectively, much higher than that of Na-rich phase (12 % and 61 %). Furthermore, Mössbauer spectra unveil that, during discharge processes at high voltages, more Fe3+reduction in Fe-rich phase is the intrinsic reason for larger plateau length and lower voltage decay. Density functional theory (DFT) calculation results demonstrate that the higher reduction ability of Fe3+ in Fe-rich phase at high voltages is due to the better reversibility of the two-phase transition between β-NaFeP 2 O 7 and Fe-rich phase than that between β-NaFeP 2 O 7 and Na-rich phase. These allow Fe-rich phase with higher energy densities, lower voltage decay and better cycling stability at high voltage plateaus. Our work provides a new idea for safe design, low-cost and long cycle life sodium ion cathode battery materials. [Display omitted] • The high voltage discharge platform is effectively prolonged in the Fe-rich phase Na 1.4 Fe 1.3 P 2 O 7. • The capacity and average voltage retentions of the Fe-rich are much higher than that of the Na-rich cathode. • Observed biphasic transition behavior in reaction, and the intermediate phase is identified as β-NaFeP 2 O 7. • The high correlation between phase transition, Fe3+ reduction, and electrochemistry performance is disclosed. [ABSTRACT FROM AUTHOR]

For polycrystalline lithium-rich manganese-based layered oxides (LMLO), the presence of porous microstructures always leads to the greater oxygen release and lower conductivity, impairing their rate and cycling stability performance for real applications. Here, by temperature-controlled annealing, we propose a facile and scalable method to infuse molten SeO 2 into the intracrystalline grain boundary of the polycrystalline Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 (LMNCO) particles. Then the uniform surface and double nanolayer structure composed of interconnected Li 2 SeO 4 and robust Li 2 Ni x Co y O 4 are revealed on primary particles. Accordingly, SeO 2 -infused LMNCO(Se-LMNCO) gains an upraised rate performance with 97 % capacity retenting rate after charge and discharge under 0.1–5 C then returned to 0.1 C and an improved cycling stability with a capacity retention of 80.0 % over 200 cycles at 1 C (1 C=250 mAh g−1). Our work highlights the significance of surface engineering inside the secondary LMLO particles and the improvement of electrochemical rate and stability performance toward lithium-ion batteries with LMLO electrode. [Display omitted] • By a facile reaction injection strategy, molten SeO 2 is successfully infused into grain boundaries of primary particles. • Then double nanolayers consisting of interconnected Li 2 SeO 4 and robust Li 2 Ni x Co y O 4 form on primary particles. • Li 2 SeO 4 nanolayers as Li-ion transport channel prevents direct contact and side reactions between material-electrolyte. • Li 2 Ni x Co y O 4 nanolayers with fast 3D Li+ diffusion channel firmly bridges the outermost Li 2 SeO 4 nanolayer to the bulk. • Greatly improved rate performance and stability are achieved for Li-rich manganese-based layered oxide cathode materials. [ABSTRACT FROM AUTHOR]

Doping is a very effective way to optimize the electrochemical performance of electrodes by tuning the electron configurations on an atomic scale. Here, to obtain excellent Co 3 O 4 electrodes for lithium ion storage, a meaningful defect-engineering of carbon-doping Co 3 O 4 microrods strongly coupling with nitrogen-doped carbon (C–Co 3 O 4 @N–C) is designed and validated. Compared with unmodified Co 3 O 4 microrods, the defect-rich C–Co 3 O 4 @N–C microrod electrode features a remarkably high initial Coulombic efficiency of 84.5% and specific capacity of 1130 mAh g−1 at 0.2 A g−1, excellent cycling stability (1265 and 1036 mAh g−1 capacity retention after 110 and 500 cycles at 0.2 A g−1 and 1 A g−1, respectively) and superior rate capacity (452 mAh g−1 capacity retention after 3000 cycles at 5 A g−1). These results demonstrate that introducing rich defects by carbon dopants and nitrogen-doping carbon can effectively modulate the electron structure and accelerate the carrier transport of materials. This valid stratagem greatly elevates lithium-ion battery performance and can be further extended to other transition metal oxides and fields. Image 1 • Carbon doping effectively tunes electron configurations of Co 3 O 4 , improving electron conductivity. • Unique microrod structures can self-adapt to volume expansion during cycles. • Ultralow nitrogen-doped carbon accelerates carrier diffusion of Co 3 O 4 electrodes. • Coupling nitrogen-doped carbon with carbon doped Co 3 O 4 features high Li-storage properties. [ABSTRACT FROM AUTHOR]