Polarity-switchable photoelectrochemical sensing of H2S in fruits via electrochemical in-situ construction of BiOI/Bi2S3 heterojunction

This study presents a polarity-switchable photoelectrochemical (PEC) method for determining hydrogen sulfide (H 2 S) in fruit matrices by electrochemically programming BiOI into a BiOI/Bi 2 S 3 heterojunction on FTO. BiOI nanosheets were first deposited potentiostatically and then partially sulfidized in Na 2 S under a mild cathodic bias, forming a tightly coupled BiOI/Bi 2 S 3 heterostructure with an in-situ generated surface Bi 2 S 3 layer. The heterojunction broadens visible-light absorption and strengthens interfacial charge separation, leading to a cathodic-to-anodic photocurrent inversion that greatly improves signal discrimination at 0 V bias. Under optimized conditions, the device shows a linear range of 0.05–30 μM with a 5.42 nM LOD, high selectivity, and stable on/off cycling. Applied to real samples, H 2 S levels of 2.13, 1.54, and 1.32 μM were obtained for apple, pear, and kiwifruit, with 93.8%‒107.4% recoveries by standard additions. This simple, low-bias PEC platform couples in-situ structural conversion with polarity switching for rapid quality monitoring and early spoilage assessment.