Polystyrene-Templated Microstructure Engineering of Aerosol-Deposited WO_3-x Films for Enhanced Hydrogen Sensing

High-performance hydrogen sensors are crucial for the safe operation of lithium-ion batteries with regard to thermal runaway monitoring, which has driven extensive research. In this work, in order to satisfy the urgent requirement of H₂ sensors for lithium-battery safety monitoring, a polystyrene sacrificial phase was introduced to fabricate porous WO₃-based sensing films with tunable oxygen stoichiometry. Through PAD (Powder Aerosol Deposition) followed by sintering in air at 500 °C, the pore structure and defect chemistry of WO_3-x films were simultaneously regulated. Structural characterizations show that polystyrene can be completely removed during sintering without changing the main γ-WO₃ phase, while interconnected pores are generated and the films evolve from near-stoichiometric WO₃ toward oxygen-deficient WO_3-x with increased oxygen-vacancy concentration. Meanwhile, the PAD-derived amorphous matrix encapsulated nanocrystalline is largely preserved, providing stable charge-transport pathways. The porous structure improves hydrogen diffusion and reaction accessibility, while bulk reduction and oxygen-vacancy enrichment enhance surface reactivity and charge transfer, together leading to improved H₂ sensing performance. Among all samples, WP5 exhibits the best overall performance, achieving stable H₂ detection over a wide range of 10 ppb to 20,000 ppm at 120 °C, together with extraordinary response. These results demonstrate that this strategy is an effective route for simultaneously engineering porosity and defect chemistry in WO_3-x-based sensing films, and highlight the potential of Pd/PS-WO_3-x sensors for lithium-ion battery thermal runaway warning.