A thermodynamic approach toward selective and reversible sub-ppm H2S sensing using ultra-small CuO nanorods impregnated with Nb2O5 nanoparticles

Abstract

This paper provides an ideal solution to the challenges of employing CuO nanoparticles for the reversible, selective, and stable detection of sub-ppm H₂S gas. This scheme presents a hidden thermodynamic advantage that makes both sulfidation and oxidation reactions reversible over a wide range of temperature (100–220 °C) by the addition of Nb₂O₅ nanoparticles coupled with Gibbs free energy changes. Our optimized sensor composed of CuO–Nb₂O₅ composites at 220 °C exhibits excellent selectivity toward H₂S and SO₂ gases, ultralow detection concentration of 500 ppb, fast response time (<180 s) and fast recovery, and reliable long-term stability (of over a month). Our spectroscopic investigations along with theoretical studies confirm that the CuO–Nb₂O₅ interface enables the formation of Cu²⁺/Nb⁴⁺ ↔ Cu⁺/Nb⁵⁺ species due to the charge transfer between the Nb and Cu species, which energetically favors CuO sulfidation and oxidation. The Gibbs free energy calculation for the sulfidation and regeneration reaction shows that the incorporation of Nb₂O₅ alters the reaction equilibrium over a wide range of temperature. Thus, our study provides insight into a thermodynamic strategy for designing metal oxide composite catalysts for improved catalytic reactions.