LAUSR

CdIn2S4/In(OH)3 heterojunctions were constructed via a scalable ultrasonic spray pyrolysis method combined with H2O2‐enabled in situ etching, in order to address the issues of photocorrosion, scarce active sites, and rapid charge recombination observed in pristine CdIn2S4. The optimized heterojunction, achieved using 50 µL of H2O2, demonstrates a significantly enhanced H2 evolution rate of 736 µmol g−1 h−1, which is 12 times greater than that of pristine CdIn2S4, along with stable performance throughout three consecutive catalytic cycles. Structural and chemical analyses verify the formation of a closely integrated heterojunction interface, which facilitates improved charge separation and efficient electron transfer from CdIn2S4 to In(OH)3, as further corroborated by electrochemical and photoluminescence studies. A possible mechanism for hydrogen evolution is also proposed.