Hydrogen sensor with ppb-level detection limit prepared by Pd-modified and Bi-doped oxidized Ni foam

In this work, we propose a hydrogen sensor to realize ppb-level hydrogen detection at a lower temperature. To fabricate the sensor, foamed nickel was thermally oxidized in bismuth oxide vapor to form the Bi-doped oxidized nickel foam, and Pd nanoparticles were further deposited on its surface by magnetron sputtering. This sensor possesses a unique phenomenon, that is, the response of the sensor does not decline due to repeated hydrogen charging and discharging as same as most hydrogen sensors, but keeps increasing and reaches balance eventually. The Bi3+ doping leads to a reduction in the thickness of the NiO hole accumulation layer, which contributes to the high response. The Bi5+ self-doping occurring during the repeated cycle test further promotes oxygen adsorption, so that the sensor response is continuously improved. As a result, the response of the Pd-Bi-OFN sensor to 1% hydrogen is as high as 580% in the air, and the detection limit is as low as 20 ppb at a lower temperature of 75 °C. Meanwhile, the sensor possesses high selectivity, great humidity stability, and long durability. This work provides an outstanding guidance to fabricate reliable ppb-level hydrogen sensors.