Development of hydrogen sensors based on polymeric and ceramic proton conductors
An all-solid-state hydrogen sensor working under short circuit amperometric conditions at low temperature with minor water maintenance has been developed. A simple and upscaleable method for the preparation of platinum metal nanoparticles were deposited onto the surface of a perfluorinated ion-exchange membrane without a binder by impregnation-reduction (I-R) of a cationic precursor salt. The I-R method, utilizes reactions of a tetraammine platinum(II) chloride hydrate [Pt(NH3)4]Cl2 solution as an impregnating salt with sodium borohydride NaBH4 and potassium borohydride KBH4 as a reducing agent on the membrane surface. The possibility of electroless deposition on layered perovskite Dion-Jacobson (D-J) phase materials was demonstrated by a multistep-impregnation-reduction (M-I-R) method. A series of A-site ordered D-J phase layered oxide perovskite compound A´[An-1BnX3n+1] (where A´ = H, Na, K, Rb, Cs; A = Ca, Sr; B = Nb, Ta) was synthesised by both solid state and soft chemical ion exchange reactions. High proton conductivity of 6.3x10-5 Scm-1 at 45 oC was obtained with KCa2Nb3O10 in H2 containing atmospheres. Electrode and electrolyte surfaces were characterized by XRD, optical microscopy, SEM, EDX and AFM. The chemically reduced sensing electrode from NaBH4 reductant was found to be suitable for high H2 concentration detection. The average max. sensitivity was observed to be 0.01, 0.007, and 0.008 µA cm-2 ppm-1 in the H2 partial pressure range from 1-2, 3-7 and 8-10%, respectively. For leak detection purposes, the sensing electrode prepared by using KBH4 reductant was found to be suitable in low ppm level H2 detection. An average max. sensitivity of the sensor 0.0046 µA cm-2 ppm-1 was achieved within 10-50 s. A reproducible, identical max. output current was observed upon changing the H2 concentration from 0 to 50 ppm. The sensing performance of proton conducting niobate KCa2Nb3O10 was proved in the presence of H2 concentration from 0.005 to 8 % at 45 oC. The max. sensitive current of 9.32 µA cm-2 was achieved within 5 s. The polymer based sensor has shown a relatively slow response yielding higher sensitive current, in contrast, the response of ceramic based sensor was fast and resulted in a lower current. Hydrogen gas detection of up to 80 % could be detected in the presence of 10-20 % CO2 gas. Interface models have been proposed for both polymer and ceramic based ionic conducting systems. The dissociated H2 molecule species transport along the surface was faster than the bulk diffusion process. The simple construction of the cell and its performance characteristics make the device very promising for portable and compact H2 sensor applications.