We report on the synthesis of CdO–CdSe nanoporous architectures from porous CdO architectures by a controlled solution anion exchange method. Monolithic CdCO₃ micron sized crystals synthesized in the first step were decomposed by calcination to evolve CO₂ to form porous CdO crystals, having a similar outer shape but with a tailored internal nanostructure. Controlled Se²⁻ ion exchange with CdO crystals yielded CdO–CdSe architectures with tunable composition and optoelectronic properties. Pearson's acid–base concept is used as a guiding principle for controlling the morphology and composition of the formed architectures. The photoelectrochemical properties of the system comprising CdO–CdSe architectures were investigated at various stages of ion exchange intervals. CdO–CdSe architectures on indium tin oxide (ITO) is a promising photoelectrode with excellent photovoltaic properties exhibiting a short-circuit current density of 7.36 mA cm⁻² under 1 Sun illumination.