An All-Organic Polydopamine/Poly(heptazine imide) Heterojunction for High-Sensitivity Photoelectric H ₂ Detection at Room Temperature

The highly sensitive photoelectric detection of hydrogen (H₂) at room temperature (RT) is highly desired, but it is crucial to boost •O₂^- generation by improving charge transfer and favorable O₂ adsorption. Herein, we construct a novel all-organic polydopamine/poly(heptazine imide) (PDA/PHI) nanosheet heterojunction through in situ polymerization for photoelectric H₂ detection. The optimized one exhibits high sensitivity (an ultralow detection limit of 500 ppm and a high gas response of 42.8% for 5000 ppm H₂), along with good linearity from 500 to 5000 ppm, under 405 nm irradiation at RT based on the dynamic detection process. Moreover, good repeatability in 40 cycles, long-term stability (over 210 days), and high selectivity are confirmed. The outstanding performance is attributed to the efficient Z-scheme charge transfer and the promoted O₂ adsorption for facilitating the •O₂^- species generation. Interestingly, the in situ μs-transient absorption spectra quantitatively reveal that the electron transfer efficiency (ETE) to the adsorbed O₂ of the PDA/PHI heterojunction is changed from 68.0% to 31.1% after introducing H₂, while the change rate of ETE is more pronounced than that of PHI. This study demonstrates great potential of all-organic heterojunctions for RT photoelectric detection and provides deep insight into the •O₂^- species and gas sensing property.