Turning on Selective H<sub>2</sub>S Gas Sensing Activity in Ternary Nickel Tungstate Strongly Correlated Electron System Through Sub-Gap Band Manipulation

Abstract

Sensing the precise concentration of chemicals within a complex atmosphere stands as a critical technology with far-reaching implications in environmental, agricultural, and medical domains. While sensitivity limits are pushed down to the ppb levels through diverse material tuning approaches, ensuring robust selectivity for targeted analyte gases remains a challenge due to the absence of effective methodologies. Here, a band structure modulation is presented in the selective detection of H2S utilizing NiWO4-based compound, achieved through strategically manipulating sub-gap states. The approach involves tailoring the sub-gap within NiWO4 by employing point defect engineering mechanisms of Cu substitutional and Li interstitial doping. Unlike the featureless pristine and Cu-doped NiWO4, Li/Cu-co-doped NiWO4 exhibits a sensing response to H2S gas, exhibiting an approximately six-fold increase in sensitivity. Through density functional theory calculations and Mott-Schottky analysis, it is unveiled that this high sensitivity and selectivity toward H2S stem from the generation and positioning of Cu d-orbital-derived sub-gap states, matching the reduction potential of H2S, which is triggered in the presence of substitutional Cu and interstitial Li. This result suggests a novel strategy for customizing sensing materials based on the reduction potential of analyte gases.