Sviluppo di elettrocatalizzatori sostenibili per la produzione di idrogeno verde

The effects of global warming are devastating ecosystems and driving the transition from fossil fuels to renewable energy. Achieving a carbon-neutral energy system requires efficient devices for storing and converting renewable energy. Hydrogen, produced via water electrolysis, is a promising zero-emission energy carrier. However, its production is hindered by slow reaction kinetics, necessitating costly noble metal catalysts. Transition metals, abundant and cost-effective, are a viable alternative, especially when optimized as single-atom catalysts (SACs). SACs maximize catalytic activity, significantly enhancing efficiency compared to bulk materials and nanoparticles, offering a scalable solution for the energy transition. This PhD thesis centers on developing efficient and durable catalysts for green hydrogen production in alkaline electrolyzers, emphasizing the relationship between catalytic activity and precise control of active sites. By correlating material structure with performance through extensive characterizations, the work aims to establish a systematic framework for catalyst design. The ultimate objective is to achieve tailored catalytic properties for practical applications, linking nanoscale to macroscale characteristics. A progressive approach grounded in structure-activity principles guides the design and investigation of electrocatalysts throughout the thesis. Initially, a detailed investigation was conducted to understand the interactions between single metal atoms and their coordination environments. Single Ni atoms were stabilized in a carbon nitride matrix synthesized via a low-temperature method and evaluated as oxygen evolution reaction (OER) catalysts under alkaline conditions. Experimental and theoretical approaches provided an accurate model of the material's structure and properties, including its restructuring during catalysis. Results revealed a linear increase in activity with Ni loading, up to a maximum of 1 wt.% Ni, which the carbon nitride framework could effectively stabilize. These SAC-based catalysts demonstrated good stability with partial Ni site restructuring. Following the demonstration of carbon nitride's effectiveness in stabilizing Ni single atoms, efforts have focused on enhancing Ni centers' catalytic activity by engineering their coordination environments, akin to molecular catalysts. A novel triazine-thiadiazole-based organic polymer was synthesized to study sulfur incorporation into the Ni coordination sphere. This modification effectively enhances catalytic performance and stability by altering the electronic density of the Ni centers. To further improve the performance and industrial viability of SACs, the materials have been incorporated into composite structures with carbon nanotubes (CNTs). This integration allows to combine the high activity and stability of Ni stabilized in carbon nitride with the superior electrical conductivity and surface area of CNTs. The resulting composite materials have demonstrated markedly improved catalytic performance, as evidenced by a substantial increase in specific current density due to enhanced electrical conductivity, greater surface area, and improved accessibility of Ni active sites to the electrolyte. The final phase of this work focused on bridging fundamental research with industrial applications. In collaboration with Acca Industries S.r.l., chemically treated stainless steel was investigated as a scalable platform for applying structure-activity principles to enhance catalytic performance in alkaline electrolyzers. The improvements were linked to newly formed surface metal phases that promote beneficial electronic interactions among Fe, Cr, Ni, and Mo, enhancing charge transfer and catalytic pathways. This integrative and systematic approach highlights the potential of structure-activity relationships to advance scalable hydrogen production technologies, addressing the pressing global demand for sustainable energy solutions.