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Abstract:

One of the main impediments facing the large-scale production of hydrogen (H2) via water electrolysis is the use of expensive platinum metal as an electrocatalyst. Early transition metal carbides and phosphides with platinum-like catalytic behavior have emerged as economic and earth-abundant alternatives to Pt. However, most of the synthetic procedures employed to produce these catalysts have led to bulky and low surface area products due to the agglomeration and coalescence of the metal during crystallization, which restrains their application for catalytic H2 reaction.

We, therefore, developed novel preparation protocols to improve the dispersion of the active sites on the carbon supports. We showed that highly porous frameworks of MIL-53, a metal organic framework, could be used as a template to guide the formation of highly dispersed molybdenum carbide (Mo2C) embedded within the mesoporous carbon. The other strategy was based on the complexation method. Molybdenum was coordinated with oxalate group using oxalic acid, which modified the self-assembling of molecular precursor and controlled the nucleation and growth of Mo2C and molybdenum phosphide (MoP) on CNTs. In addition, we demonstrated the growth of interconnected hollow scaffold of cobalt phosphide (CoP) on CNTs. Hexamethylenetetramine as used as a structure-directing agent. Plausible growth mechanisms were proposed. The methods are simple with the potential to scale-up. Composition were characterized using standard techniques, such as transmission and high-resolution transmission electron microscope, field emission scanning electron microscope, powder X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and so forth.

The potential of as-prepared electrocatalysts was evaluated as low-cost electrodes for hydrogen evolution reaction (HER), both in acidic and basic electrolytes. It was demonstrated that smaller particle size with better dispersion, hollow and interconnected artifacts impart benign attributes, such as enhanced specific and electrochemically active surface area, low intrinsic charge transfer resistance, high interfacial charge transfer kinetics, and improved mass transport, to electrocatalysts. As a result, the electrode comprising as-synthesized compositions exhibited remarkable electrocatalytic performance, outperforming most of the electrocatalyst reported as yet.

The findings offer fresh impetus to engineer Pt-free electrode materials with high activity for large-scale and sustainable H2 production through electrolysis.




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