Oxygen Vacancy Defects Boosted High Performance p‑Type Delafossite CuCrO2 Gas Sensors

X-ray diffraction (XRD) measurement was conducted in a D8 ADVANCE X-ray diffractometer, operated at 40kV and 40 mA. Morphology was observed by field-emission scanning electron microscope (FESEM, JEOL JSM-6007F) and transmission electron microscope (TEM, JEM-2011 200 kV). The Brunauer−Emmett−Teller (BET) surface area was analyzed by Micromeritics ASAP 2460 nitrogen adsorption−desorption apparatus. Thermogravimetric analyses (TGA, NETZSCH STA449F3) were carried out from room temperature to 600 °C in air atmosphere and to 1000 °C in N2 atmosphere, respectively; the heating rate was 10 °C/min. X-ray photoelectron spectroscopy (XPS) measurement was conducted on a Esca Lab 250Xi spectrometer (Thermo Scientific) using amonochromatic Al Kα X-ray source (1486.6 eV) operating at a pressure of ∼2 × 10−7 Pa. An Ar ion gun (beam energy range of 0.1− 4 keV) was equipped with the XPS spectrometer, which allows etching away the possible surface contaminations of the samples. Electron spin resonance (ESR) spectroscopy of CCO powders wasobtained using a JEOL JES-FA200 ESR spectrometer (300 K, 9.063 GHz, X-band). UV−vis absorption spectra were recorded with a Shimadzu UV-3101PC spectrophotometer. The PL spectra were measured by a Horiba Jobin Yvon Fluorolog-3-TAU fluorescence spectrophotometer at room temperature (excitation wavelength is 320 nm).First, the assynthesized CCO nanoparitcles were mixed with appropriate isopropyl alcohol and sonicated for 60 min to form a paste. Then the paste was coated onto a ceramic substrate (with predefined platinum interdigital electrodes and heating electrode) to form a sensing layer. Supporting Inforamtion Figure S1 gives the photographand schematic image of the sensor device. The thickness of the sensing layer could be adjusted by the brushed cycles. After the natural drying of the paste in air, the device was aged at 350 °C for 3h in a tube furance either in air or vacuum (around 2 Pa) to ensure a good stability. Finally, the gas reponse properties were examined in atesting system (SD101) produced by Huachuang Ruike Science and Technology Wuhan Co., Ltd. The concentration of VOCs flowing into the sensing chamber was tuned by adjusting the flow rate ratio of the target gas to the reference gas (dry air) controlled by mass flow controllers (MFCs). During the measurements the total flow rate ofthe target gas and dry air was fixed to be 1000 cm3(STP) min−1. The sensitivity or response (S) of the gas sensor is defined as Rg/Ra, where Rg and Ra are the resistances of the sensor in the target gas and in the reference gas, respectively. The response/recovery time of the sensor(τres/τrec) is defined as the time required for a resistance change of 90%.