Effect of hydroxyl groups on the oxygen vacancy and hydrogen-sensitive properties of CeO2 in different morphologies

The “hydroxyl-oxygen vacancy model” was of great importance for the catalytic and physicochemical properties of metal oxides. Here, we proposed a simple method to construct a hydroxyl-oxygen vacancy model for one-step reduction of palladium chloride through ascorbic acid rich in hydroxyl, loaded on rod, spherical, nanoparticles and cubic CeO₂, to achieve the Ce⁴⁺/Ce³⁺ transition and the generation of Pd NPs. The surface-loading Pd ions activated the lattice oxygen of CeO₂, and promoted the overflow of reverse oxygen at the Pd–O–Ce interface. The increasing in Ce³⁺ occupancy altered the reduction performance, oxygen vacancy number and active Pd valence state of the catalyst, and greatly contributed to the response and recovery times. Among the obtained sensors, the 0.50 wt % Pd/CeO₂–C/R sensor show a response amplitude of 190/196% to 1000 ppm H₂ at 120 °C with a response/recovery time of only 1/3 s. These excellent results are mainly attributed to the chemisorbed oxygen and Ce³⁺ after ascorbic acid reducing Pd are found to be 4.84 and 1.57 times higher than pure CeO₂. The hydroxyl-oxygen vacancy model may open up a new avenue for detecting hydrogen sensing.