Optimizing coupling effect of confined FeNi nanoalloys within graphitic carbon nanofibers to improve photothermal energy conversion efficiency for solar water purification

•FeNi nanoalloys were encapsulated in graphitic carbon nanofibers derived from Prussian blue analogue (PBA).•Limited oxidation and aggregation of FeNi nanoalloys in CNF were obtained by changing PBAs loading.•Synergistic effect between non-noble plasmonic nanoalloys and graphitic carbon nanofibers was constructed by electrospinning.•Optimized photothermal conversion efficiency was reached by the constructed composited fiber membrane.•A extremely low usage dosage of photothermal materials can enable the construction of 2D evaporation membrane.