The pH-dependent properties of cuprous oxide thin films prepared by electrochemical deposition for liquid petroleum gas sensing

Efficient liquid petroleum gas sensing was investigated by modulating the pH level (8, 9, 10, 11, and 12) of electrochemically deposited nanostructured cuprous oxide thin films in a lactate bath. The synthesized films were characterized by surface contact angle, XRD, SEM, UV-Vis absorption, Mott-Schottky, and AC impedance spectroscopy measurements. These displayed a unique initial increment or decrease followed by a persistent decrement or increment at pH 9-10. This turning pH point exhibited the least wetting polycrystalline Cu2O growth with the smallest crystallite size of similar to 45 nm, the highest dislocation density of similar to 50 mu m(-2), and a strain of 0.03 according to X-ray diffraction. SEM micrographs identified similar to 1 mu m-sized, closely structured grains with trigonal-prismatic shapes. The Mott-Schottky plots drawn from C-V measurements revealed a significant dependence of flat band potential and free carrier density on the deposition bath pH level. Cu2O films deposited using the lactate bath changed the conductivity at pH 9 from n-type to p-type when increasing the pH value. With the conductivity transition, films prepared at pH 9 displayed a relatively high direct band gap energy of 2.28 eV. Liquid petroleum gas (LPG) sensing at 70 degrees C demonstrated the most substantial gas response of 11.5 % at pH 10 Cu2O films. Cu2O thin films deposited at pH 9 emerged as the most stable and reproducible p-Cu2O LPG sensor, with response and recovery times ranging from 20 to 25 seconds. Remarkable changes in the film structures and morphologies were revealed with pH values above 9 after the gas exposure. The grain shape and distribution of pH 9 remained unchanged, assuring the stability of the sensing platform.