Hydrogen sensing with palladium-coated optical fibers

Abstract

Palladium-coated, single-mode optical fibers have been used to detect hydrogen in a concentration range 20 parts per billion to 2% in 1 atm of nitrogen. When the coated fibers are exposed to hydrogen, a hydride is formed with an expanded lattice constant, which stretches the optical fiber. This change in optical path length is measured using a Mach–Zehnder interferometer. A simple one-dimensional model is presented and shown to accurately reproduce the fiber response. Using electrodeposited palladium films, a factor of 7 enhancement in the hydrogen solubility is observed, as well as a deeply bound site which is saturated in the parts per million concentration range. The data suggest that this site may be due to hydrogen binding to a free surface of the palladium.