Designing metal-substituted WB2 and MoB2 asefficient bifunctional electrocatalysts for hydrogenand oxygen evolution reactions

Over the past few years, the ever-increasing global energy demand, environmental problems, and climate change have fostered researchers to focus on designing economic and competent catalysts to produce pure energy originating from renewable energy sources. Transition metal diborides (TMDbs) have recently attracted the scientific community's attention because of their remarkable attributes as bifunctional catalysts for both oxygen and hydrogen evolution reactions (OER/HER) with excellent durability in alkaline media. The prominent features, such as superior electronic conductivity and a high density of active sites, are dominated in the 3D framework of MDbs due to the presence of due to the presence of borophene subunits as. In this thesis, metal substituted WB2 and MoB2 were investigated under the alkaline medium as promising electrocatalysts for OER/HER by comparing different substitution transition metals (Ni and Co), variety for concentration in the structure (x = 0, 0.1, 0.2, and 0.3 even higher for MoB2), and two alternative synthesis techniques (molten salt-assisted (ms) and carbothermal reduction (ct)). The aim was to control the crystal structure and morphology, and tailor the electronic structure to optimize adsorption-desorption features on the surface. The results unraveled a general fact that materials synthesized by the molten-salt technique turned to be relatively better catalysts toward OER/HER. In particular, W0.8Co0.2B2/ms demanded the lowest respective overpotentials of 340 and 363 mV to generate a current density of 10 mA cm-2 for OER/HER. While Mo0.8Co0.2B2/ms provided 340 mV to reach 10 mA cm-2 for OER, Mo0.9Ni0.1B2/ms ensured 220 mV overpotential for HER as a further improvement. Besides enhancement in overpotentials, W0.8Co0.2B2/ms displayed durability of 12 h against OER/HER. For MoB2 electrocatalysts, Mo0.9Ni0.1B2/ms showed excellent HER stability for 12 h. Thanks to controlling the nano-size of the particles, their homogeneous distribution throughout the samples, and keeping the layered structure for both metal diborides, the molten saltassisted technique led to electrocatalysts with better electrocatalytic activity compared to the carbothermal reduction. These results demonstrate that layered metal diborides possess great potential as electrocatalyst toward hydrogen and oxygen evolution reactions.