Since polarization is the reason of refraction, then anything that changes the structure of molecule, atom, or electron will present as a change of reflection. Thus, to my understanding, chemical reaction of electrolyte will accompanied by a refractive index change. I monitored the refractive index of NaCl solution before and after a 4.5 V voltage was applied. The sensitivity of the refractive index sensor is known as 1100 nm/RIU, which is enough to detect a 10 ppm (10$^-$$^5$) refractive index change. But nothing was detected.
Now I'm not quite sure if the refractive index will be changed due to chemical reaction. Or is the sensor still not sensitive enough? Thanks!