H2 oxidation pathways on Ni-ceria surface by electrical conductivity relaxation method

The reaction of H2 oxidation on samaria-doped ceria (SDC) surface deposited with scattered Ni particles is studied utilizing the electrical conductivity relaxation method. The surface reaction rate is remarkably improved by the Ni particles. The improvement linearly increases, but is not directly proportional to the length of Ni-SDC-gas boundary (3 PB), suggesting there are three pathways for the H2 oxidation, the original reaction on bare SDC-gas (2 PB) interface, the reaction through 3 PB and the 2 PB reaction with hydrogen atoms migrating from Ni surface via spillover. The original 2 PB reaction contribution decreases significantly from 100% for the bare SDC to 13% after Ni deposition and further to 3% at the Ni particle density of 417 μm−2. Meanwhile, the Ni related reaction from 3 PB and 2 PB spillover contributes up to 97%, demonstrating that Ni can greatly accelerate the H2 oxidation reaction. The 3 PB contribution decreases while the 2 PB spillover contribution increases with the increase of the average Ni particle distance, i.e. the decrease of 3 PB length and number of Ni particles per surface area. The 3 PB and 2 PB spillover contributes almost equally when the average distance is 76 nm and particle density is 66.1 μm−2. The results show the reaction on Ni-SDC could be dominated by both 3 PB and 2 PB spillover pathways. The 2 PB spillover may dominate the total reaction for model patterned electrodes and the 3 PB should control hydrogen reaction for nanostructured electrodes fabricated by impregnation method.