Spatially Programmable S-Scheme Heterojunction Photoanodes via Aerosol-Jet Printing for Efficient Solar Water Oxidation.

S-scheme heterojunctions enable efficient charge separation while preserving the strong redox ability of photogenerated carriers, offering a powerful platform for advanced photoelectrochemical (PEC) water splitting. However, translating such rationally designed heterostructures into scalable, high-performance photoanodes remains a critical bottleneck for conventional fabrication methods. Here, we develop an aerosol-jet printing (AJP) approach to fabricate S-scheme SrTiO3/g-C3N4 heterojunction photoanodes with well-controlled stacking sequences. The interfacial built‑in electric field drives recombination of SrTiO3 photogenerated electrons with g‑C3N4 holes, preserving the strongly oxidizing holes in SrTiO3 for the oxygen evolution reaction (OER). The SrTiO3-on-C3N4 configuration delivers enhanced PEC water oxidation activity, with a photocurrent density of 2.3 mA cm- 2, double that of single-component and reversed-structure photoanodes. It is found that this enhancement stems from stacking-order-dependent synergy between the heterojunction built-in electric field and semiconductor-electrolyte band bending. Notably, AJP enables fabrication of large-area, module-sized photoanodes, demonstrating practical scalability for device manufacturing. This work provides a controllable, scalable route for the rational design of high-performance S-scheme heterojunction photoelectrodes for PEC water splitting.