Faced with the global energy crisis, the search for efficient technologies as substitutes for fossil fuels is increasingly incessant. Based on this premise, this present work addresses the controlled synthesis of two nanomaterials that were used as catalysts for energy conversion applications. Thus, the first work describes the synthesis of Pd nanoflowers in a single reaction step by reducing Tetrachloropalladate ion with hydroquinone. By simply controlling the reaction temperature, it was possible to obtain monodisperse Pd nanoflowers with well-defined shapes and sizes. Based on the detected product morphology, crystallinity and several control experiments, a new non-classical mechanism based on LaMer and DLVO theories was established. In this procedure, temperature control allowed adjusting the ionic strength of the solution (control of the fraction of Tetrachloropalladate ion and K+ ions present in the solution), which affected the fixation and aggregation steps, leading to to Pd nanoflowers with controlled control. sizes and morphologies. When these nanomaterials were employed as nanocatalysts for ethanol electrooxidation, 12 nm Pd nanoflowers were the best catalyst in terms of activity and peak potential. In the second work, MnO2 nanowires decorated with Ir nanoparticles (1.2 percent by weight) measuring 1.8 ± 0.7 nm were used for the oxygen reduction reaction (ORR). It was observed that the MnO2—Ir nanohybrid showed high catalytic activity and improved stability for ORR compared to commercial Pt/C (20 percent by weight of Pt). The superior performance provided by the MnO2—Ir nanohybrid may be related to (i) the significant concentration of reduced Mn3+ species, leading to an increase in the concentration of oxygen vacancies on its surface; (ii) the presence of strong metal-support interactions, in which the electronic effect between MnOx and Ir can enhance the ORR process; and (iii) the unique structure composed of ultrasmall sizes of Ir on the nanowire surface that enable the exposure of high-energy surfaces/facets, high surface-to-volume ratios, and their uniform dispersion.