Hydroxide membrane fuel cells (HEMFCs) operated in alkaline media enables the use of the non-noble catalyst for oxygen reduction reaction (ORR). Therefore, it seems promising that HEM technology can replace the Pt-metal dependent proton exchange membrane (PEM) technology. However, the sluggish hydrogen oxidation reactions (HORs) on Pt-metal catalysts in the alkaline electrolyte, which are up to two orders of magnitude slower than in the acid electrolyte, requires a higher loading of precious metals on the anode of HEMFCs. This, to a larger extent, offsets the cost gains from employing non-precious metal on the cathode of HEMFCs. In order to tackle this challenge, we prepared Pd₅₀Cu₅₀ alloy nanoparticles (NPs) and characterized them for HOR in 0.1 M potassium hydroxide. The HOR activity exhibited a strong dependence on the annealing temperature. In particular, Pd₅₀Cu₅₀ alloy NPs annealed at intermediate temperature outperforms Pt and Pd. The conventional lab-based XRD shows the annealed Pd₅₀Cu₅₀ alloy features a special crystalline phase. And the synchrotron sources based x-ray further revealed the time-resolved phase change of Pd₅₀Cu₅₀ alloy as the temperature was ramped from 30°C to 950°C. Analysis of STEM and XPS, along with the theoretical modeling based on density functional theory (DFT), provides a new insight into the correlation between the crystalline structure of Pd₅₀Cu₅₀ alloy with HOR activity in alkaline media.