Nanoparticles (NPs) can be used as nanocatalysts in renewable energy applications due to their ability to tune the surface interactions during catalysis. However, synthesizing NPs in a controllable manner and understanding how properties change with size and structure is challenging. Therefore, mapping out the synthesis, structure, and property relations of the NPs is important to get better use of NPs. In this thesis, synthesis parameter studies were carried out to investigate how synthetic conditions control the structure of NPs. In situ X-ray total scattering together with pair distribution function (PDF) analysis were used to study the formation mechanisms of bimetallic NPs. Lastly, binary NPs were examined under catalytic conditions to link their structure and catalytic behaviors. First, the formation mechanism of PdIn NPs was investigated. By carefully selecting the metal ion precursors and surfactants used in the synthesis, the phase of PdIn bimetallic NPs could be controlled. Then, in situ X-ray total scattering was used to study surfactant-driven formation pathways. A Bain-strain phase transformation process was discovered, where a Pd3 In fct phase formed first and then transformed into an intermetallic PdIn CsCl-type phase. This study revealed that local chemistry not only affects the outcome phase of the synthesis but also has an impact on the phase transformation process. Next, the synthesis and structure relations of PdGa NPs was investigated. From a synthetic parameter study, it was shown that monodisperse intermetallic Pd2 Ga NPs could be synthesized. In addition, through ex situ powder X-ray diffraction patterns (PXRD) and transmission electron microscopy (TEM), it was illustrated that structural and morphological tunning could be achieved by varying the local ligand environment. Finally, the synthesis, structure, and property relations of NiFe oxyhydroxides (NiFeOOH) were elucidated. A solvothermal method was applied. By varying synthesis times and metal precursor ratios, NiFeOOH samples with different sizes and morphologies were obtained. These NiFeOOH samples were used to catalyze the xygen evolution reaction (OER) in alkaline media, to study the relations between the samples’ structure and the Fe impurities in the electrolyte. Thus, a purification procedure was conducted for the electrolyte, KOH. It was found that Fe impurity promotes NiFeOOH samples’ OER activity differently owing to their structural differences. The highest activity does not match with the highest electrochemical surface area, indicating that the structure of the sample matters for electrocatalysis.