Synthesis, characterization and hydrogen sensing properties of nanosized colloidal rhodium oxides prepared by Pulsed Laser Ablation in water

Nanosized colloidal rhodium oxide particles in water were obtained by using a nanosecond pulsed excitation, starting from a high purity rhodium target. The as-synthesized colloids show an almost spherical shape and size in the range between 2 and 12 nm. Characterization results indicate that colloidal particles are composed mainly of oxidized RhxOy phases, whose content increase after annealing at 200 °C in air and decrease under hydrogen treatment in mild conditions, suggesting a reversible behavior. The hydrogen sensing characteristics of thin films deposited by drop casting from the colloidal solution onto alumina sensor substrates provided with platinum interdigitated electrodes, were also investigated. The developed conductometric hydrogen sensor shows high response to low concentration of the target gas in air at low operating temperature and full reversibility with fast dynamics. Further, a good selectivity towards hydrogen was demonstrated, testing other simple molecules such as CO, CO2, NO2 and O2. To our knowledge, this is the first report on the use of nanosized rhodium/rhodium oxide colloids in conductometric gas sensors. © 2018