Solar-driven water evaporation provides a promising solution to the energy crisis and environmental issues. Capitalizing on the high photothermal conversion efficiency and excellent resistance to strong acids or strong alkalis of Pt3Ni–S nanowires, we strategically design and prepare a flexible Pt3Ni–S-deposited Teflon (PTFE) membrane for achieving efficient strong acid/alkaline water evaporation under simulated sunlight irradiation (1 sun). By comparing the surface morphology, mechanical properties, and water evaporation performance of the as-prepared three different membranes, we have screened out a high-performance photothermal membrane that has good hydrophobicity (water contact angle = 106°), strong mechanical properties, high light-to-heat conversion efficiency (η = 80%), and excellent durability (10 cycles in a range of pH = 1.2–12). In particular, we explore the mechanism of high surface mechanical properties of the as-prepared membrane using density functional theory. The results demonstrate that the related mechanism can be ascribed to two main reasons: (1) hydrogen bonds can be formed between the 2-pyrrolidone ring and PTFE-3 and (2) the O atom in PTFE-3 carries more negative charge (−0.19 |e|) than PTFE-1 (−0.16 |e|) and PTFE-2 (−0.15 |e|). Our work highlights the great potentials of a Pt3Ni–S-deposited PTFE membrane as a device for implementing solar energy-driven evaporation of industrial wastewater with strong acidity or alkalinity and provides a new strategy for improving the surface mechanical properties of a photothermal membrane.