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Nb 2 O 5 nanowires (NWs) were grown by the thermal oxidation of Nb foils. The thermal chemical vapor transport of CdS/CdSe powders produces Nb 2 O 5 -CdS x Se 1Àx core-shell NWs with complete composition tuning. In the alloy composition, CdSe-like and CdS-like phases exist in the outer and inner regions of the shell, respectively, forming unique multi-shell structures. As x increases, the thickness of the CdSe-like outer shell decreases, while that of the CdS-like inner shell increases. We fabricated photoelectrochemical (PEC) cells using the as-grown Nb 2 O 5 -CdS x Se 1Àx NWs and measured their photocurrents and hydrogen generation rates under AM 1.5G irradiation. The PEC cells showed excellent photoconversion efficiency, which is comparable to that of TiO 2 -CdS x Se 1Àx NWs. It indicates that the present Nb 2 O 5 NW promises an excellent photoanode of solar cell devices. The multi-shell structures increase the PEC performance by producing novel band alignment for efficient electron-hole separation following enhanced visible-range photon absorption.