Intermediate Phase-Ordering in Pd–Cd–Zn Electrocatalysts for Accelerated Alkaline Hydrogen Evolution

A controlled disordered-to-ordered phase transition offers a promising approach for designing catalysts for water electrolysis. Starting from disordered face-centered cubic ( fcc ) Pd, an ordered tetragonal Pd 1.06 Cd 0.94 intermetallic alloy forms at 220 °C. Introducing Zn increases the ordering temperature, yielding tetragonal Pd 1.02 Cd 0.968 Zn 0.012 only at 260 °C. At 220 °C, an intermediate-composition (PCZ-mix-1) contains 69.4 wt % fcc Pd 0.51 Cd 0.47 Zn 0.02 and 30.6 wt % ordered tetragonal Pd 0.98 Cd 1.02 . PCZ-mix-1 nanoparticles exhibit superior alkaline hydrogen evolution reaction (HER) activity, driven by charge transfer across disordered–ordered interfaces. At the fcc – tetragonal interface, charge accumulation on Pd and depletion on Cd favor *H adsorption at the Pd sites and *OH at the Cd sites. PCZ-mix-1 delivers 36 ± 8 mV and 173 ± 10 mV overpotentials at 10 and 100 mA cm –2, respectively, high mass activity (111.9 A g –1 ), turnover frequency (TOF; 1.2 H 2 s –1 ), and hydrogen evolution of 52 mL h –1 at −250 mV RHE, maintaining stability for >200 h at −0.175 V RHE .