P2-Na_0.67Ni_0.33Mn_0.67O₂ cathode holds the merits of high working voltage/capacity, facile manufacture, and similar large-scale production to Li layered oxides. However, it suffers from issues of irreversible P2–O2 phase transition at a high voltage (>4.0 V), interfacial instability, and particle cracks after repeated cycle. Herein, in-situ formed MgO surface coating layer and Mg²⁺ subsurface gradient doping is obtained by Mg₃(PO₄)₂ decomposition under 900 ℃. The as-formed in-situ surface coating and subsurface doping effects simultaneously guarantee the high-stability of material interface and structure. HRTEM and HAADF-STEM images clearly show the surface coating layer is 2‒5 nm and subsurface gradient doping depth is 3‒5 nm, rather than bulk doping. In-situ XRD patterns and in-situ DRT analysis profoundly clarify the enhanced electrochemical reaction stability and structural reversibility. Theoretical calculations elucidate superior electronic and spatial structures after in-situ surface coating and subsurface doping engineering. As a result, the optimized cathode shows ascendant discharge capacity of 100.3 mAh·g^–1 at 1C with 80.8% retention during 500 cycles. It displays much improved rate capability of 81.5 mAh·g^–1 at 5C. Revealing excellent cycling stability and potential applications for high-performance sodium-ion batteries.

Electrochemical CO₂ reduction reaction (CO₂RR) to high-value product, CO, not only provides a key feedstock for the well-established Fischer–Tropsch process but also mitigates the greenhouse effect. However, it suffers from sluggish reaction kinetics, competitive hydrogen evolution reaction, and low selectivity. Herein, we report non-precious Cu-Sn diatomic sites anchored on nitrogen-doped porous carbon (CuSn/NPC) as an efficient catalyst for CO₂RR to CO. The catalyst exhibits outstanding selectivity with CO Faradaic efficiency (FE) up to 99.1%, much higher than those of individual Cu (66.2%) and Sn (51.3%) single-atom catalysts. Moreover, high stability is confirmed by consecutive 24 h electrolysis with high selectivity from CO₂ to CO. Theoretical calculations reveal an obvious activation of CO₂ with weakened C–O bonds and distorted CO₂ configuration upon chemisorption on the CuSn/NPC catalyst. It is also suggested CuSn/NPC is more selective for the CO₂RR with dominant CO production during the electrolysis, rather than the competing hydrogen evolution reaction.