Structural engineering and electronic tuning of non-noble transition metal-based electrocatalysts

Catalysis, a process that can accelerate chemical reactions, has become a pivotal role in producing renewable energy (e.g. fuel cells, solar energy, biofuels, etc.) s by environmentally friendly routes. Heterogeneous electrocatalysis has prompted intensive efforts, owing to their low thermodynamic requirements, cost-effective energy, high coulombic efficiency, and reduced carbon footprint. However, the unfavorable kinetics of most electrochemical reactions severely limits the large-scale applications of energy conversion devices. To reduce the reaction barrier, efficient electrocatalysts, with high active-site accessibility, abundant surface areas, good electrical conductivity, desirable electrical conductivity and long-term stability, are necessarily required. This dissertation offers a dual-tuning strategy combining structural design and electronic tuning of non-noble-metal-based electrocatalysts. To push the mass/charge transfer of non-noble-meal-based catalysts for practical applications, strategies including structural engineering and optimized electronic modification are applied to achieve efficient and stable electrocatalysts. Porosity engineering is firstly introduced in 2D transition metal-based electrocatalysts to alleviate the restacking issue of the 2D nanomaterials, offering large active surface areas and fast ion transfer (Chapter 3). Besides, to overcome the inferior electron transfer during the electrochemical process, electronic modification, such as anionic substitution, is employed to boost the electron transfer. By applying structural engineering and electronic modification in 2D electrocatalyst, both mass transport and charge transfer are improved. The density of state and the local electronic/atomic structure optimizations of electrocatalysts are further studied by modeling computation. To extend the structural design and electronic modification to a broad range of electrocatalysts, gel-based electrocatalysts with enhanced mass/charge transfer are further introduced. Unlike conventional electrocatalysts prepared from bulky powders suffering from severe issues on mass transport and electron transfer, gel-based electrocatalysts offer larger numbers of active sites, due to unique hierarchical structures, compositional tunability, ease of functionalization, and high wettability for electrolyte penetration (Chapter 4). By introducing functional dopants or alloying with transition metals, not only the electron transfer of gel-derived alloys can be improved, but also the N adsorption energy can be regulated (Chapter 5). Finally, key strategies combining structural design and electronic tuning of non-noble-metal-based electrocatalysts are summarized and possible future directions are provided (Chapter 6).Mechanical Engineerin