Investigation of catalytic activities of WC-based catalysts at bio-inspired liquid-liquid interfaces

Increased use of fossil fuels and the serious threats posed by resulting environmental problems have accelerated the search for alternative energy sources. Hydrogen, due to its high calorific value and environmental friendliness, is considered a significant intermediate energy carrier and a potential alternative to fossil fuels. Among hydrogen production methods, hydrogen production reactions at liquid-liquid interfaces, which possess properties similar to biological membranes, stand out with important advantages. These include reusability, elimination of pre-processing steps such as cleaning solid electrodes, and serving as a transitional step for electrolyzer applications. The most well-known catalysts used in catalytic hydrogen production are precious metals such as Pt and their alloys. However, despite their high catalytic activities, the limited natural abundance and high costs of these precious metal catalysts restrict their widespread use. Recently, the catalytic activities of Mo- and W-based sulfides, selenides, and carbides have garnered significant attention as alternatives to precious metals. Due to unique electronic structure and thermal/chemical stability properties, WC is an important candidate in catalytic applications, but the reduced proton adsorption with less active surface area is a limiting factor for its catalytic activity. In this context, recent studies have focused on strategies such as doping with metal doping, heterojunction design. This thesis investigates, for the first time, the activity of WC-based catalysts (WC/Ni, WC/Co, and WC/NiCo) designed with transition metals inspired by hydrogenase enzymes in hydrogen production reactions at liquid-liquid interfaces. Their optical, electrochemical, and chromatographic properties were analyzed and compared. Furthermore, the in situ synthesis method was explored for composite catalyst design. Electrodeposition, used as a synthesis method, eliminates challenges such as complex procedures during synthesis, the formation of auxiliary catalysts with large particle sizes, and the uneven distribution of catalysts at the interface. In addition to the catalyst designs inspired by hydrogenase enzymes, this thesis introduces, for the first time, the formation of auxiliary catalysts (MoSx, Pt, and Cu) directly on WC catalysts via electrodeposition, using precursor salts without requiring an additional synthesis procedure. Subsequently, hydrogen production studies at liquid-liquid interfaces were conducted. The catalysts designed in this thesis demonstrated a significant increase in hydrogen production performance at liquid-liquid interfaces compared to catalyst-free reactions, suggesting that they could serve as alternatives to precious metals. The structural and morphological properties of the catalysts, whose catalytic activities were proven, were characterized using advanced techniques such as X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Energy-Dispersive X-Ray Spectroscopy (EDX).