Mechanistic understanding of gas sensing in palladium nanoparticles-decorated porous ZnO nanosheets: Correlating energy barrier and ionized oxygen species with sensing performance

• Porous ZnO nanosheets decorated with Pd nanoparticles were fabricated via a combined hydrothermal and microwave-assisted synthesis method. • Pd nanoparticle decoration modulates the energy barrier for carrier transport and alters the dominant ionized oxygen species involved in gas sensing reactions. • A mechanistic understanding of optimal sensing materials and devices was achieved by correlating surface reaction parameters with measured sensing performance. Nanoscale heterostructures composed of noble metals and metal oxides are widely employed to enhance gas sensing performance. However, the fundamental sensing mechanisms underlying these improvements remain incompletely understood. Herein, we investigate the surface reaction characteristics of porous ZnO nanosheets (P-ZnO NSs) decorated with Pd nanoparticles (NPs), focusing on two key parameters: the energy barrier for carrier transport ( E b ) and the dominant ionized oxygen species, inferred from the power law exponent n in the relation R = A P O 2 n ,where R is the resistance and P O 2 is the oxygen partial pressure. Our results show that Pd NPs decoration significantly modulates E b , and both E b and n are strongly correlated with gas sensing behavior. Temperature- and concentration-dependent measurements reveal that an increased Δ E b enhances the response toward acetone, while the optimal sensing temperature can be inferred from the n value. A maximum sensing response of ∼ 0.16 was achieved at 450°C in the sample with ∼3.1% Pd surface coverage, which exhibited the highest Δ E b (0.60 eV) and an n value of 0.26, corresponding to dominant ionized oxygen species of O 2− . For NO 2 sensing, the same sample also exhibited the largest response at 250°C, suggesting that surface band modulation plays dominant role in oxidizing gas detection as well. In contrast, NH 3 sensing was comparatively suppressed, which is attributed to competing oxidative surface pathways that partially counteract the electron-donation effect of NH 3 .