Hydrogen is emerging as a key solution to meet the global transition toward clean and sustainable energy. In this context, the present work investigates hydrogen production by solar-assisted water electrolysis in the presence of dispersed metal oxide powders. Four identical electrolyzers were operated under natural solar irradiation (Condition 1: 11:00–18:00; Condition 2: 11:00–17:00) at a constant applied current of 1.5 A. Three metal oxides (ZnO, MgO, and CuO) were tested individually and then with 1 wt% Al₂O₃ to evaluate the effect of Al₂O₃ addition. As single oxides, MgO exhibited the highest cumulative improvement (+46.74% vs. the Witness cell), followed by CuO (+19.57%) and ZnO (+16.30%). After Al₂O₃ addition, higher normalized hydrogen production was observed under the investigated conditions: ZnO–Al₂O₃ showed the largest increase (+123.69% vs. ZnO alone, irradiance-normalized basis), followed by MgO–Al₂O₃ (+59.78%) and CuO–Al₂O₃ (+47.93%). These results indicate that the effect of Al₂O₃ addition on hydrogen productivity is strongly oxide-dependent, and identify ZnO–Al₂O₃ as the most promising system among those tested. Overall, the study provides new insights into the design of oxide-assisted electrolysis systems and supports their potential for further development of solar-driven hydrogen production.