Although single-atomically dispersed metal-N_x on carbon support (M-NC) has great potential in heterogeneous catalysis, the scalable synthesis of such single-atom catalysts (SACs) with high-loading metal-N_x is greatly challenging since the loading and single-atomic dispersion have to be balanced at high temperature for forming metal-N_x. Herein, we develop a general cascade anchoring strategy for the mass production of a series of M-NC SACs with a metal loading up to 12.1 wt%. Systematic investigation reveals that the chelation of metal ions, physical isolation of chelate complex upon high loading, and the binding with N-species at elevated temperature are essential to achieving high-loading M-NC SACs. As a demonstration, high-loading Fe-NC SAC shows superior electrocatalytic performance for O₂ reduction and Ni-NC SAC exhibits high electrocatalytic activity for CO₂ reduction. The strategy paves a universal way to produce stable M-NC SAC with high-density metal-N_x sites for diverse high-performance applications.

The oxygen redox (OR) activity is conventionally considered detrimental to the stability and kinetics of batteries. However, OR reactions are often confused by irreversible oxygen oxidation. Here, based on high-efficiency mapping of resonant inelastic x-ray scattering of both the transition metal and oxygen, we distinguish the lattice OR in Na_0.6[Li_0.2Mn_0.8]O₂ and compare it with Na_2/3[Mg_1/3Mn_2/3]O₂. Both systems display strong lattice OR activities but with distinct electrochemical stability. The comparison shows that the substantial capacity drop in Na_0.6[Li_0.2Mn_0.8]O₂ stems from non-lattice oxygen oxidations, and its voltage decay from an increasing Mn redox contribution upon cycling, contrasting those in Na_2/3[Mg_1/3Mn_2/3]O₂. We conclude that lattice OR is not the ringleader of the stability issue. Instead, irreversible oxygen oxidation and the changing cationic reactions lead to the capacity and voltage fade. We argue that lattice OR and other oxygen activities should/could be studied and treated separately to achieve viable OR-based electrodes.

The hybrid line commutated converter (H-LCC) topology has been verified to reduce the commutation failure probability effectively, but the reverse blocking integrated gate commutated thyristor (RB-IGCT) that meets the requirements of this topology has not yet been developed. This study focuses on the optimal design of the RB-IGCT with high blocking voltage, large on-state current, and high turn-off capability. First, an emitter isolation (EI) structure is proposed to tune the low-level injection efficiency, and the forward leakage current can be reduced by 50% without degrading the on-state current. Then, a method for optimizing anode emitter is presented. A high-doped and shallow p+ emitter is preferred to control the current gain while ensuring a low on-state voltage. As to the turn-off capability, the corrugated p-base (CB) structure is used to independently improve the maximum controllable current (MCC). In addition to the corrugation amplitude, the effect of the corrugation width is verified by experiments. Finally, 8 kV RB-IGCT samples are fabricated and tested, which reach over 3 kA average on-state current and 5.5 kA MCC. This study not only provides a practical guidance to the design of the RB-IGCT but also promotes the development of the HVDC transmission system.