From endeavors of the last quarter of the century gone by, newly released “jewelry” of the materials science, namely, self-assembled and self-supported giant nanoarchitectures have received tremendous interest from all areas of nanoscience and nanotechnology. Indeed, recently developed approaches for the fabrication of nanomaterials have opened new horizons for controlling efficiently the growth mechanism of nanoparticles, which paves the way for miscellaneous and manifold metallic nanostructures with tunable sizes, morphologies, and compositions. These excellent commands on the structure, even at the atomic level, enable tuning precisely and effectively their unique electronic, optical, and catalytic properties, thus enabling drastic enhancement in both activity and durability. To cope and to overcome the scarcity and high price of platinum group metals (PGMs), materials' scientists inelectrocatalysis are now focusing their intense research efforts on the design of high-performance electrocatalysts with minimal precious metal content. Since electrocatalysis involves mostly surface phenomena, this consists of maximizing the utilization efficiency by engineering advancedPGM nanoobjects with high thresholds of exposed atoms at the surface for groundbreaking devices. This has paid off in terms of “easy-to-use” hierarchically nanoporousPGM structures by using intelligent and elegant approaches. Specifically, the past decade has witnessed a remarkable drive for the elegant design of giant mesoporous (from one to three dimensions) interconnected elementary and cornerstone building blocks yielding to the so-called nanoframes, nanocages, nanoballs, and so on. Approaches are based on replication methods using hard and/or soft templates, described as molds for nanocasting processes. Because of their high surface area and tunable porosity, nanoporous metallic materials are expected to provide large number of active sites and aid diffusion during the entire catalytic process. This chapter reviews recent advances in the design and use of nanoporous metallic materials to elaborate robust electrode materials for the electrochemical energy conversion technologies. Special attention will be given to our developed radiolysis process for advanced nanostructures preparation with scalable physical structure that enables the effective synthesis of various core–shell mesoporous nanostructures ranging from simple to nanoballs. In other words, nanostructures are fabricated by arranging atoms one-by-one exactly where we want them, the hallmark of any technological and fundamental breakthroughs, as opposed to a top-down engineering where a piece of raw material is drilled, milled, and chipped away until what is left is what is needed.