Toward Theoretical Capacity and Superhigh Power Density for Potassium-Selenium Batteries via Facilitating Reversible Potassiation Kinetics.

Potassium-selenium (K-Se) batteries attract tremendous attention because of the two-electron transfer of the selenium cathode. Nonetheless, practical K-Se cells normally display selenium underutilization and unsatisfactory rate capability. Herein, we employ a synergistic spatial confinement and architecture engineering strategy to establish selenium cathodes for probing the effect of K+ diffusion kinetics on K-Se battery performance and improving the charge transfer efficiency at ultrahigh rates. By impregnating selenium into hollow and solid carbon spheres with similar diameters and porous structures, the obtained parallel Se/C composites possess nearly identical selenium loadings, molecular structures, and heterogeneous interfaces but enormously different paths for K+ diffusion. Remarkably, as the solid-state K+ diffusion distance is significantly reduced, the K-Se cell achieves 96% of 2e- transfer capacity (647.1 mA h g-1). Reversible capacities of 283.5 and 224.1 mA h g-1 are obtained at 7.5 and 15C, respectively, corresponding to an unprecedented high power density of 8777.8 W kg-1. Quantitative kinetic analysis demonstrated a twofold higher capacitive charge storage contribution and a 1 order of magnitude higher K+ diffusion coefficient due to the short K+ diffusion path. By combining the determination of potassiation products by ex situ characterization and density functional theory (DFT) calculations, it is identified that the kinetic factor is decisive for K-Se battery performances.

Inversely Tuning the CO2 Electroreduction and Hydrogen Evolution Activity on Metal Oxide via Heteroatom Doping.

Tuning the electronic states near the Fermi level can effectively facilitate the reaction kinetics. However, elucidating the role of a specific electronic state of metal oxide in simultaneously regulating the CO2 electroreduction reaction (CO2 RR) and competing hydrogen evolution reaction (HER) is still rare, making it difficult to accurately predict the practical CO2 RR performance. Herein, replacing the Zn site by heteroatoms with different outer electrons (Mo and Cu) is found to tune both occupied and unoccupied orbitals near the Fermi level of ZnO. Moreover, the different electronic states significantly modulate both CO2 RR and HER activity with a totally inverse trend, thus dramatically tuning the practical CO2 RR performance. In parallel, the correlation between electronic states, reaction free energies and practical activity is demonstrated. This work provides a possibility for engineering efficient CO2 RR eletrocatalysts through tunable composition and electronic structures.