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In this work we highlight a peculiar synthesis protocol for the p-type ternary metal oxide system of copper bismuth oxide (CuBi 2 O 4 ), which yields a highly crystalline spherulitic morphology at a low temperature of 78 C. We associate this growth with the hydrogen bonding effects imparted by the ethanol-water cosolvent system used for the synthesis. We present a detailed growth mechanism by evaluating different synthesis conditions systematically. Furthermore we show that upon the use of the non-stoichiometric (excess copper) precursor mixture under the same experimental conditions the growth of spherulitic CuBi 2 O 4 changes the size and type of the spherulites. Interestingly, careful optimization of the nonstoichiometric synthesis presents a complete impediment to the spherulitic growth and produces a composite of nanorods of CuBi 2 O 4 and nanosheets of CuO. This anisotropic nanocomposite shows an order of magnitude higher surface area as compared to spherulitic CuBi 2 O 4 . Since both CuBi 2 O 4 and CuO are visible light absorbing p-type semiconductors, when the synthesized nanocomposite materials are examined as photoelectrochemical (PEC) photocathodes for water splitting, they show a remarkable dependence on the morphology and phase constitution. Almost 13-fold stronger PEC response is observed as the morphology changes from spherulites to nanorods. † Electronic supplementary information (ESI) available. See Scheme 1 Schematic of morphology evolution by precursor ratio control. 3662 | J. Mater. Chem. A, 2014, 2, 3661-3668 This journal is

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