| Summary: | 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.
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