Electrofabrication of Ni-Based Alloy Coatings for Anticorrosion and Water Splitting Applications

Abstract

This thesis titled ‘Electrofabrication of Ni-based alloy coatings for anticorrosion and water splitting applications’ presents a comprehensive study on development and characterization of two Ni-based alloy coatings from newly formulated baths, namely (Ni-Mo) and (Ni-Fe). Standard Hull cell method was used to optimize bath constituents and operating conditions for best performance of alloy coatings against corrosion, as well as for good electrocatalytic activity for water electro-splitting applications. The corrosion protection efficacy of monolayer Ni-based alloy coatings were improved further by modern methods of electroplating, namely magneto-electrodeposition (MED) and composition modulated multilayer electrodeposition (CMM-ED) approach. Poor corrosion resistance of (Ni-Mo) alloy coatings, limited by the low concentration of metal ions was successfully alleviated by taking the advent of magnetic field (B) effect, applied simultaneously to the process of deposition. Experimental investigation revealed that corrosion protection efficacy of monolayer (Ni-Mo) alloy coatings can be improved about 5 times and 8 times better, through MED technique by superimposing the B, parallel and perpendicular (to the direction of movement of metal ions), respectively. The attractiveness of electroplating linked to the cathode current density has been explored effectively for the development of multilayer (Ni-Fe) alloy coatings of better corrosion resistance, compared to their monolayer counterpart. The multilayer (Ni-Fe) alloy coatings of much higher corrosion resistance were developed by proper manipulation of composition and thickness of alternate layers of alloys by proper modulation of amplitude and duration of current pulse, respectively. In addition, the electro-catalytic activity of (Ni-Mo) and (Ni-Fe) alloy coatings have been tested for their efficacy for both HER and OER in water splitting applications in 1.0 M KOH. The effect of composition, surface morphology and phase structure of alloy coatings on their electro-catalytic efficacies have been studied, using CV and CP methods. The effect of addition of redox-active polyoxometalates (POM), and Ag-nanoparticles into electrolytic baths of (Ni-Mo) and (Ni-Fe) on electro-catalytic activities of their coatings were studied, and reasons responsible for improved activities were discussed. Corrosion performance of all coatings were studied by electrochemical AC and DC methods in 3.5 % NaCl, and results were compared. The process and product of electrodeposition were characterized using SEM, EDS, AFM and XRD techniques. The performance of alloy coatings developed under different conditions of current density are compared, and results are discussed with Tables and Figures.