Phase-tailored CoCrFeNiAl nitride for enhanced electrocatalytic hydrogen evolution <i>via</i> cooling-mediated plasma strategy

Modulation of the surface structure of high-entropy-alloy-based nitrides (HEANs) is considered essential for improving electrocatalytic H₂ production. Compared with thermal nitridation, the plasma technique is a favorable alternative to directly fabricate HEANs, but the excessive surface heating effect during plasma treatment inevitably causes thermally stabilized nitride formation, resulting in deterioration of the highly active structure. To optimize the hydrogen evolution reaction (HER) behavior of HEANs, a facile cooling-mediated plasma strategy is proposed to precisely modulate the HEAN structure (cp-HEAN). The resultant cp-HEAN framework shows a preserved FCC (111) facet and yields an increased amorphous proportion, leading to enhanced HER behavior. In comparison, the normal plasma technique causes FCC lattice distortion with increased precipitation owing to the excessively high surface thermal field (np-HEAN). <i>Operando</i> plasma diagnostics and numerical simulation further confirmed the effect of surface heating on typical plasma parameters and the HEAN framework, indicating that this was the key factor responsible for the high performance of the nitride electrocatalyst.