Electrodeposition of nickel-iron alloys using deep eutectic solvent as a catalyst for oxygen evolution reaction (OER) in water splitting

• Main Author: Sebastian Dario Suarez Hidalgo
• Other Authors: Chia-Ying Chiang
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/4j5ran

碩士 === 國立臺灣科技大學 === 化學工程系 === 106 === Efficient and durable water electrolysis is a key technology for sustainable clean energy production. In order to have an efficient electricity- gas conversion, materials that require low overpotential to make water splitting possible must be used. Materials for the cathodic reaction that provides good energetic efficiency have already been synthesized. However, the sluggish kinetics in the anode reaction is still a limiting to make water splitting economical viable. Iridium and ruthenium oxides are the benchmark materials for anodes in water splitting. Nevertheless, the high cost and scarcity of this materials increase the industrial cost of the process. The fabrication of economical materials with high activity is crucial to achieve the viability of water electrolysis. From earth abundant elements, materials composed by nickel and iron are the ones that present the best prospect as anodes for water splitting, and being possible to outperformed the benchmark Ir and Ru oxides catalyst. Deep eutectic solvents (DES) are a new family of ionic liquids. In the last decades, they have become attractive because they are considering a green solvent. DES possess a wide potential window, which make possible the electrodeposition of many metals without hydrogen evolution in the cathode. Various metals with decorative and specific purposes have already electrodeposited from them. In the present work, First, a suitable potential for electrodeposition of Ni and Fe alloys in ethaline DES solution was determined by cyclic voltammetry and confirmed with electrochemical impedance spectroscopy. Then, the electrodeposition of the Ni, Fe and Ni-Fe alloys was carried out at conditions that allows to obtain a well attached to the substrate and uniform films. The metal composition of the alloys electrodeposited is found to be directly proportional to the metal concentration in the ethaline solution.The as-deposited films then were characterized by SEM. Ni and Fe samples present nodular and grain-crystal morphology respectively. Ni films present a face cubic center crystallinity, iron film esasly oxidize into magnetite crystalline structure and Ni-Fe alloys presents a crystalline phase of Ni Fe. The films were tested as electrocatalyst for oxygen evolution reaction in alkaline media. It has been found that the alloy with Ni:Fe 3:1 metal ratio presents the lowest overpotential of the analyzed alloys, with a overpotential value of 316 mV at 10 mA∙cm-2 and a Tafel slope value of 62 mV∙dec-1 and durability on a 0.1 M NaOH electrolyte. XPS shows after OER a change valence state from Ni metal to Ni+2 due to oxidation of the surface, while Fe is present in Fe+3 before and after OER.