Bimetallic Alloy Nanoparticles as Bifunctional Electrocatalyst for Overall Water Splitting

Kumar, Arun (2018) Bimetallic Alloy Nanoparticles as Bifunctional Electrocatalyst for Overall Water Splitting. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

The synthesis of morphology based nanostructured alloy nanoparticles showing superior activity towards Hydrogen Evolution Reaction (HER) with earth abundant elements carrying long term stability and low cost is highly desirable to full fill our energy requirements. In this work AgxNi₁-x bimetallic nanoparticles in the form of alloy nanostructure with varying Ag concentration having a five-fold twinned morphology as well as FexCo₁-xOnanoparticles have been synthesized. The Ag₀.₀₅Ni₀.₉₅ bimetallic nanoparticles exhibit excellent and unique electrocatalytic performance for hydrogen evolution in alkaline media and its activity matches with state of the art benchmark commercial Pt/C catalyst. For HER, Fe₀.₈Co₀.₂Oy and Ag₀.₀₅Ni₀.₀₉₅ alloy electrocatalysts exhibit high activity with an overpotential of only 58 mV and 20.9 mV respectively at 10 mA cm² while commercial Pt/C needs overpotential of 20.1 mV in 1M KOH at 10 mA/cm² on carbon fiber paper (CFP). For electrochemical oxygen evolution reaction (OER), Fe₀.₂Co₀.₈Oy and Ag₀.₀₅Ni₀.₉₅ alloy electrocatalysts demonstrate an overpotential of 332 mV and 364 mV respectively. Also, for overall water splitting of Ag₀.₀₅Ni₀.₉₅ electrolyzer (taking at both cathode and anode) needs 1.7 V cell voltage. Theformation of AgxNi₁-x multiply twinned nanostructured bimetallic alloys have been confirmed with Powder X-ray diffraction (PXRD), high resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray analysis (EDS). The HRTEM, high-angle annular-dark-field imaging (HAADF) with single particle point EDS analysis reveals in five-fold twinned Ag₀.₀₅Ni₀.₉₅ having predominately Ag at the edge and Ni at the face surface which suggest the catalytic activity of twinned surfaces originates due to the increased availability of Ni sites. This study provides the explanation of outstanding performance of multiply twinned alloy nanoparticles at nanoscale and may lead to use of these nanostructured bimetallic alloy nanoparticles in various catalytic performance with long term durability and excellent energy efficiency.

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