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This study demonstrates an atomic composition manipulation on Pt–Ni nano-octahedra to enhance their electrocatalytic performance. By selectively extracting Ni atoms from the {111} facets of the Pt–Ni nano-octahedra using gaseous carbon monoxide at an elevated temperature, a Pt-rich shell is formed, resulting in an ∼2 atomic layer Pt-skin. The surface-engineered octahedral nanocatalyst exhibits a significant enhancement in both mass activity (∼1.8-fold) and specific activity (∼2.2-fold) toward the oxygen reduction reaction compared with its unmodified counterpart. After 20,000 potential cycles of durability tests, the surface-etched Pt–Ni nano-octahedral sample shows a mass activity of 1.50 A/mgPt, exceeding the initial mass activity of the unetched counterpart (1.40 A/mgPt) and outperforming the benchmark Pt/C (0.18 A/mgPt) by a factor of 8. DFT calculations predict this improvement with the Pt surface layers and support these experimental observations. This surface-engineering protocol provides a promising strategy for developing novel electrocatalysts with improved catalytic features. 

An effective paradigm is proposed to design strong and ductile alloys using unstable fault energies. 

Sodium ion batteries have attracted much attention in recent years, due to the higher abundance and lower cost of sodium, as an alternative to lithium ion batteries. However, a major challenge is their lower energy density. In this work, we report a novel multi‐electron cathode material, KVOPO₄, for sodium ion batteries. Due to the unique polyhedral framework, the V³⁺↔ V⁴⁺↔ V⁵⁺redox couple was for the first time fully activated by sodium ions in a vanadyl phosphate phase. The KVOPO₄based cathode delivered reversible multiple sodium (i.e. maximum 1.66 Na⁺per formula unit) storage capability, which leads to a high specific capacity of 235 Ah kg⁻¹. Combining an average voltage of 2.56 V vs. Na/Na⁺, a high practical energy density of over 600 Wh kg⁻¹was achieved, the highest yet reported for any sodium cathode material. The cathode exhibits a very small volume change upon cycling (1.4% for 0.64 sodium and 8.0% for 1.66 sodium ions). Density functional theory (DFT) calculations indicate that the KVOPO₄framework is a 3D ionic conductor with a reasonably, low Na⁺migration energy barrier of ≈450 meV, in line with the good rate capability obtained.