Key Considerations in Developing Photothermal Membrane Distillation

Interfacial photothermal membrane distillation (PMD) has emerged as a promising solar-driven desalination technology, yet its performance varies widely because of inconsistent testing conditions, incomplete heat-transfer accounting, and limited understanding of key design parameters. This perspective consolidates fundamental considerations essential for reliably evaluating and advancing PMD systems. Here, we clarify the distinctions among PMD, solar steam generation, and interfacial solar stills and emphasize solar-to-water efficiency as the appropriate performance metric. Using a one-dimensional mass and heat transfer model, this perspective article highlights how airgap thickness, membrane porosity and pore size, feedwater residence time, and salinity jointly control vapor flux and thermal efficiency. It further discusses practical challenges in PMD development, including accurate surface-temperature measurement, membrane robustness under long-term operation, and fouling behaviors unique to interfacial heating. We also address the complementary role of data-driven approaches in PMD design and performance evaluation. Based on insights from theoretical modeling and reported experimental systems, we suggest strategies for optimizing module design, enhancing latent-heat recovery, and improving the durability of photothermal membranes. By establishing new unified guidelines for performance evaluation and identifying key scientific and engineering opportunities, this perspective aims to accelerate the development of efficient, scalable, and sustainable PMD systems for solar desalination.