Cyclic electro-deposition (CED) is a cost-effective tool to synthesize nanostructures with a solution process, controllable morphology and high purity. Here we report novel platinum nanostructures fabricated according to CED at room temperature in solution containing H₂PtCl₆ precursor and NaNO₃. Remarkable Pt nanostructures—from nanoclusters, nanosheets, nanograsses to nanoflowers—were produced through morphological control via variation of either period of CED scans or concentration of the precursor. Pt films with uniform nanograss structures have great electro-catalytic performance (electron-transfer resistance = 0.3 Ω) and intrinsic light-scattering (reflectivity ∼50%), perfectly suitable for use as counter-electrodes for dye-sensitized solar cells (DSSCs). The DSSC device made with the Pt-nanograss counter-electrode and N719 dye attained efficiency η = 9.61% of power conversion, which is 12% enhanced from that fabricated according to a conventional thermal decomposition method (η = 8.55%) under similar experimental conditions. When the devices were further optimized with a thick TiO₂ film (17 + 5 μm) sensitized by Z907 dye using the CED-Pt counter-electrode, we obtained J_SC (mA cm⁻²) = 19.44, V_OC (V) = 0.742, and FF = 0.736, giving an exceptional power conversion efficiency of 10.62%.