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Underwater vehicles are generally supplemented and driven by ocean thermal engine systems (OTES), leveraging the large thermal-energy reserves via solid–liquid phase change materials (PCMs). However, the low thermal conductivity and high-pressure melting point migration of PCMs severely limit their energy-storage performance. In this study, alkane binary mixture PCMs and enhanced heat transfer structures were integrated into the OTES to increase the energy storage power. The melting point of pure n-hexadecane was reduced using a 5% mass fraction of n-octane. The density and melting interval of an alkane binary mixture PCM at different pressures were studied using molecular dynamics simulations. An OTES coupling model based on the enhanced heat-transfer theory of metal foams was developed. The minimum relative error in the model prediction of melting time was 1.13%. The effects of different precharge pressures, nominal volumes, and energy-storage strategies of the accumulator on the energy-storage process were investigated. The results indicate that a large nominal volume, precharge pressure, and energy-storage interval are beneficial for improving the energy storage power. For 5 L accumulator, the maximum power for single energy-storage strategy is 13.92 W, while multiple energy-storage strategy improves by 41.52% to 19.7 W. • Alkane binary mixture is used to compensate for elevated melting intervals. • Metal foam enhances heat transfer of alkane binary mixture. • Molecular dynamics simulations predict the density and melting interval. • A coupling model of ocean thermal engine systems is proposed. • Factors influencing energy-storage performance are revealed. [ABSTRACT FROM AUTHOR]