Hydrogen is a highly sought-after and versatile energy carrier, as well as a crucial chemical with widespread applications. It can be produced from water through photocatalysis using sunlight or through electrolysis powered by solar or wind energy. However, the design of efficient photocatalytic systems for hydrogen production remains a significant challenge, necessitating the development of novel photocatalysts. In this study, we successfully synthesized neodymium iron composites with a platelet-like nanostructure using a sol–gel technique, followed by heat treatment at different annealing temperatures ranging from 750 to 900 °C. The analysis using Rietveld Refinements revealed the formation of a composite consisting of NdOCl/Fe2O3/NdFeO3. To investigate the effects of phase composition variations caused by different annealing temperatures, we applied various characterization techniques to explore the optical absorption properties, band structure, and photocatalytic hydrogen evolution ability. Among the samples, the one obtained at 800 °C exhibited the highest photocatalytic hydrogen evolution activity. It demonstrated a measured rate of 12.79 µmol/g/h when methanol was used as the sacrificial agent and 18.99 µmol/g/h when triethanolamine (TEOA) was applied as the sacrificial agent. To provide insight into the observed differential photocatalytic activity, we propose a possible mechanism based on the separation of photogenerated charge carriers through varied interfacial heterojunctions resulting from the phase composition change in each sample.