Searching for power-independent, compact, and highly environment-sensitive photodetectors is a critical step towards the realization of next-generation energy-efficient and sustainable integrated optoelectronic systems. Particularly, the deep ultraviolet (UV) band, which has large photon energy, is extremely suitable for environment monitoring and invisible light communication application. Herein, the demonstration of self-powered deep UV solar-blind photodetectors in a photoelectrochemical (PEC) cell configuration is reported, adopting wide bandgap n-type aluminum gallium nitride (AlGaN) nanowires as photoelectrode. After decorating nanowires with noble metal ruthenium (Ru), the constructed solar-blind PEC photodetectors exhibited excellent responsivity of 48.8 mA W-1, fast response speed (rise time of 83 ms and decay time of 19 ms) with large photocurrent density of 55 μA cm-2 at 254 nm illumination. Such superior performance can be attributed to, firstly and foremost, the successful synthesis of highly uniform and defect-free n-type AlGaN nanowires which ensures efficient photogeneration via effective light-harvesting, and secondly, the boosted carrier separation and collection efficiency through Ru decoration. This novel nanoarchitecture enables deep UV photodetection to work stably with low energy consumption, intriguingly, opening the possibility for the development of high-performance PEC photodetectors based on group III-nitride semiconductors covering the entire spectral range from infrared to deep UV.