Activating S surfaces by reversing the electron supply direction for fast hydrogen sensing

Abstract

The nature of a built-in electric field within supported metal catalysts plays a crucial role in regulating gas adsorption and electron transfer during the gas-sensing process. Herein, we found an electron-supply redeployment phenomenon involving the reversal of direction of a built-in electric field between the metal palladium species and the outer S atoms in ZnS, resulting in a marked hydrogen sensing difference. It was found that Pd nanoparticles embedded into Pd NP-ZnS can induce spontaneous electron transfer from S atoms to Pd species to generate an electron-deficient sulfur (S^(2−δ)−) surface. Conversely, atomically dispersed Pd species (Pd₁-ZnS) prefer to generate electron-rich sulfur (S^(2+δ)−) sites and thus reverse the built-in electric field. Theoretical calculations demonstrate that the electron-rich S (S^(2+δ)−) surface can reduce the occupancy of antibonding orbitals in the S–H_ads bond and enhance the bond energy of S–H_ads, thus increasing the adsorption of hydrogen. Additionally, in situ Raman, ex situ X-ray photoelectron spectroscopy and DFT analysis demonstrate that S^(2+δ)− sites in Pd₁-ZnS samples can undergo strong electron transfer with hydrogen during the sensing process. Ultimately, Pd₁-ZnS sensors exhibit extremely high response values (9.66/20 ppm) and fast response recovery times (5.1 s/1.8 s to 400 ppm) for hydrogen gas at a working temperature of 170 °C.