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 Pd1.06Cd0.94 intermetallic alloy forms at 220 °C. Introducing Zn increases the ordering temperature, yielding tetragonal Pd1.02Cd0.968Zn0.012 only at 260 °C. At 220 °C, an intermediate-composition (PCZ-mix-1) contains 69.4 wt % fcc Pd0.51Cd0.47Zn0.02 and 30.6 wt % ordered tetragonal Pd0.98Cd1.02. 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 H2 s–1), and hydrogen evolution of 52 mL h–1 at −250 mVRHE, maintaining stability for >200 h at −0.175 VRHE.