Testing solid materials in the cell to minimize iodine loss by evaporation. I expect halloysite clay ( nanotubular) to perform well. Lugol's solution, used in medicine for centuries, is 10% KI/ 5% I2 in water. Grafoil and zinc electrodes.
The zinc is a section of zinc flower pots ( Amazon) with the wax removed by use of ethyl acetate. Cheap and flexible source of Zn for electrode use.