Hydrogen (H₂) has emerged as a sustainable energy carrier capable of replacing/complementing the global carbon-based energy matrix. Although studies in this area have often focused on the fundamental understanding of catalytic processes and the demonstration of their activities towards different strategies, much effort is still needed to develop high-performance technologies and advanced materials to accomplish widespread utilization. The main goal of this review is to discuss the recent contributions in the H₂ production field by employing nanomaterials with well-defined and controllable physicochemical features. Nanoengineering approaches at the sub-nano or atomic scale are especially interesting, as they allow us to unravel how activity varies as a function of these parameters (shape, size, composition, structure, electronic, and support interaction) and obtain insights into structure–performance relationships in the field of H₂ production, allowing not only the optimization of performances but also enabling the rational design of nanocatalysts with desired activities and selectivity for H₂ production. Herein, we start with a brief description of preparing such materials, emphasizing the importance of accomplishing the physicochemical control of nanostructures. The review finally culminates in the leading technologies for H₂ production, identifying the promising applications of controlled nanomaterials.

TiO₂/SiO₂ nanoparticles with 3, 5, and 10 molar percent of silica, were synthesized by hydrothermal method and characterized by SEM, TEM, N₂ adsorption-desorption isotherms, X-ray diffraction, and Raman and UV-Vis spectroscopy. While pristine TiO₂ thermally treated at 500°C presents a surface area of 36 m² g^-1 (±10 m² g^-1), TiO₂/SiO₂ containing 3, 5, and 10 molar percent of silica present surface areas of 93, 124, and 150 m² g^-1 (±10 m² g^-1), respectively. SiO₂ is found to form very small amorphous domains well dispersed in the TiO₂ matrix. X-ray diffraction and Raman spectroscopy data show that anatase-to-rutile phase transition temperature is delayed by the presence of SiO₂, enabling single-anatase phase photoanodes for DSSCs. According to the I×V measurements, photoanodes with 3% of SiO₂ result in improved efficiency, which is mainly related to increased surface area and dye loading. In addition, the results suggest a gain in photocurrent related to the passivation of defects by SiO₂.

The optoelectronic properties of quantum dots are strongly controlled by the chemical nature of their surface-passivating ligands. In this work, we present the synthesis, characterization, and surface modification of CdSe quantum dots (QDs) and their application in solar cells. CdSe QDs were capped in oleic acid (OA), 3-mercaptopropionic acid (MPA), and 4-mercaptobenzoic acid (MBA). The QDs were characterized by transmission electron microscopy (TEM), UV-Vis absorption and emission spectrophotometry, thermogravimetric analyses, and ¹H and ¹³C NMR. From TEM analysis, it has been observed that interparticle distance can be effectively controlled by the presence of different molecular size ligands. From the ¹H and ¹³C NMR, specific types of interactions between the Cd²⁺ and the ligands have been observed. Although CdSe/OA presented larger interparticle distance as compared to CdSe/MPA and CdSe/MBA, the photocatalytic oxidation of the thiol groups on the surface of the MPA- and MBA-based quantum dots resulted in poor surface stabilization, ultimately resulting in poor power conversion efficiencies which were ca. 70% smaller than that of OA-based solar cell.

2D metal clusters maximize atom–surface interactions, making them highly attractive for energy and electronic technologies. However, their fabrication remains extremely challenging because they are thermodynamically unstable. Current methods are limited to element‐specific binding sites or confinement of metals between layers, with no universal strategy achieved to date. Here, a general approach is presented that uses vacancy defects as universal binding sites to fabricate single‐layer metal clusters (SLMC). It is demonstrated that the density of these vacancies governs metal atom diffusion and bonding to the surface, overriding the metal's physicochemical properties. Crucially, the reactivity of vacancy sites must be preserved prior to metal deposition to enable SLMC formation. This strategy is demonstrated across 21 elements and their mixtures, yielding SLMC with areal densities up to 4.3 atoms∙nm⁻ ² , without heteroatom doping, while maintaining high thermal, environmental, and electrochemical stability. These findings provide a universal strategy for stabilizing SLMC, eliminating the need for element‐specific synthesis and metal confinement protocols and offering a strategy for efficiently utilizing metals.

In this work we show that phase formation and oxygen substitution can be controlled by the source of nitrogen used during the synthesis of TiO₂ nanoparticles.