Electrocatalytic Nitrate Reduction Reaction to Ammonia with Metastable HCP Ni-Co Alloy

Sasmal, Saswati (2025) Electrocatalytic Nitrate Reduction Reaction to Ammonia with Metastable HCP Ni-Co Alloy. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Saswati Sasmal (23MP018)) 23MP018_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (2MB)

Abstract

Electrochemical nitrate reduction provides a sustainable pathway for the synthesis of ammonia, as well offers an alternative route for the energy-intensive Haber-Bosch process. However, the main challenges associated with this process are achieving higher selectivity due to the competitive hydrogen evolution as a side reaction and designing a stable electrocatalyst. In this work, we have synthesized a bimetallic alloy of Ni (atomic radius 124 pm) and Co (atomic radius 125 pm) in their metastable hcp phase, by Schlenk line. Due to the slightly larger size of Co, there is a negative shift of 2θ in the powder x-ray diffraction pattern (PXRD) with the gradual increase of Co content in the Ni lattice, suggesting the alloy formation. Further, Rietveld refinement of the PXRD pattern confirms the formation of single-phase hcp Ni and Ni1-xCox (x = 0 – 0.15) alloy. High-resolution transmission electron microscopy (HRTEM) analysis shows the presence of (010), (002), and (011) facets. In the electrochemical nitrate reduction reaction (NitRR), Ni95Co5 alloy shows the best catalytic activity among all other compositions. It exhibits a maximum ammonia faradaic efficiency of 92.98% and H2 side product as 5% at an applied potential of -0.5 V vs, RHE in 1M KOH +0.1 M KNO3 electrolyte, with ammonia yield rate 8.52 mg h-1 cm-2.

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