Metal-oxide heterostructures represent an effective strategy to overcome the limitations of pristine TiO
2, including its ultraviolet-only light absorption and rapid electron–hole recombination, which hinder its performance in solar-driven applications. Among various configurations, coupling TiO
2 with tungsten oxide (WO
x)
            
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            Metal-oxide heterostructures represent an effective strategy to overcome the limitations of pristine TiO
2, including its ultraviolet-only light absorption and rapid electron–hole recombination, which hinder its performance in solar-driven applications. Among various configurations, coupling TiO
2 with tungsten oxide (WO
x) forms a favorable type-II band alignment that enhances charge separation. However, a comprehensive understanding of how WO
x overlayer thickness affects the optical and photoelectrochemical (PEC) behavior of device-grade thin films remains limited. In this study, bilayer TiO
2/WO
x heterostructures were fabricated via reactive DC magnetron sputtering, with controlled variation in WO
x thickness to systematically investigate its influence on the structural, optical, and PEC properties. Adjusting the WO
x deposition time enabled precise tuning of light absorption, interfacial charge transfer, and donor density, resulting in markedly distinct PEC responses. The heterostructure obtained with 30 min of WO
x deposition demonstrated a significant enhancement in photocurrent density under AM 1.5G illumination, along with reduced charge-transfer resistance and improved capacitive behavior, indicating efficient charge separation and enhanced charge storage at the electrode–electrolyte interface. These findings underscore the potential of sputtered TiO
2/WO
x bilayers as advanced photoanodes for solar-driven hydrogen generation and light-assisted energy storage applications.
            
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