Abstract: Water electrolysis has attracted significant attention as a clean, efficient, and sustainable hydrogen production technology. Developing efficient and stable non-noble metal electrocatalysts for the hydrogen evolution reaction （HER） has become a major research focus. In this work, two cobalt hypophosphite （Co（H₂PO₂）₂） materials with significantly different crystallinities were synthesized on nickel foam via a hydrothermal–phosphorization route and an electrodeposition approach, resulting in a higH−crystallinity plate–rod composite structure （H−Co（H₂PO₂）₂） and a low-crystallinity microspherical structure （L−Co（H₂PO₂）₂）. Comprehensive structural characterizations and electrochemical measurements were conducted to investigate the effect of crystallinity on HER performance, revealing that H−Co（H₂PO₂）₂ possesses a more ordered crystal structure, superior electronic conductivity, and higher intrinsic catalytic activity. It requires an overpotential of only 39 mV to reach a current density of 10 mA cm^–2 and retains excellent structural stability and electrocatalytic activity after 100 h of continuous operation, demonstrating great potential for water electrolysis applications.