Ion trapping effect assisted in situ formation of dense amorphous-crystalline nanointerfaces on NiW alloy for...

NiW alloys with unique corrosion resistance have garnered considerable attention for the alkaline hydrogen evolution reaction (HER). Incorporating amorphous WO_x can overcome the performance limitations of ordered NiW alloys by exposing more active sites. However, the dissolution of tungsten oxides triggered by the K⁺ ion trapping effect is inevitable yet often overlooked during alkaline HER. Herein, a K⁺ ion trapping effect strategy is proposed for assisting in situ formation of dense amorphous-crystalline (a-c) nanointerfaces on NiW alloy (a-c(WO_x)/NiW), utilizing a WO_2.72-encapsulated NiW alloy as a pre-catalyst, wherein the a-c nanointerfaces function as a regulator of interfacial water, a diffusion channel for ions, reactive species and electrons, and an activator of active sites. During HER, K⁺ intercalation, proceeded by coupled ion-electron transfer (CIET), facilitates H₂O access to the alloy, activates the Ni₃ hollow sites for additional *H adsorption, and modulates *OH desorption at the W sites. Simultaneously, the WO_x component intervenes in the hydrogen-bond network to promote proton transfer and optimizes *H adsorption at the Ni₂W₁ hollow sites of the alloy. Benefiting from the dense a-c nanointerfaces, a-c(WO_x)/NiW delivers superior HER performance (58 ± 2 mV@50 mA cm^-2, Tafel slope 47 ± 2 mV dec^-1), approaching that of commercial 20% Pt/C. This work reveals the evolution behavior of tungsten oxides on NiW alloy surface under the K⁺ ion trapping effect and offers new insights into the design of durable HER electrocatalysts.