| dc.description.abstract | Hydrogen is an energy carrier, feedstock, industrial process gas, and alternative transportation fuel. Low-temperature water electrolysis, the splitting of water into its constituent gases hydrogen and oxygen by the means of electricity, is a sustainable and efficient hydrogen production technology critical to the large-scale deployment of hydrogen as a fuel. Recent advances and developments in anion exchange membrane (AEM) technology, i.e. the technology of membranes conducting alkaline anions such as OH-, drive the development of water electrolysis using anion-exchange membranes.
AEM water electrolysis aims to combine the benefits of classical alkaline water electrolysis and the more recent proton exchange membrane (PEM) systems by combining the low cost and stability associated with alkaline water electrolysis with the ability to operate at differential pressure, fast dynamic response, low energy losses, and the higher current densities associated with PEM water electrolysis. Achieving 1 A/cm2 at 2 V in a durable and stable AEM water electrolysis process is an important target, the achievement of which would represent a breakthrough for AEM water electrolysis technology. To reach such performance, the HER catalyst aims to achieve a current density of -10 mA/cm2 with lower than 100 mV while the OER catalyst targets a current density of 10 mA/cm2 at lower than 300 mV overpotential with fundamentally investigating catalyst composition, durability, and ionomer electrolyte interaction.
In this work, durable and active oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalysts have been developed for AEM water electrolysis. The work has focused on the rational design of stable HER and OER catalysts free of platinum-group metals (PGM), i.e. on non-PGM catalysts, with improved mass activity for the alkaline environment. For HER catalyst, the catalyst is designed and synthesized inspired by the Sabatier principle (Volcano plot) such as the NiMo catalyst or based on the bifunctional mechanism (Ni/NiO and Ni/NiO/CuO) or combining both principles in Ni-MoO2. NiFe and NiCo oxides were tested and evaluated as possible HER catalysts since these catalysts are well known OER catalysts which may pave the way to be used as for both electrodes. For the OER catalyst, The OER activity of Ni-based catalysts is tailored by combining with different transition metals.
The electrochemical characterization of catalyst involves electrochemical activity and surface area determination, stability, and interaction with ionomer and electrolyte. In situ Raman spectroscopy has been used to monitor intermediate formation and catalyst oxidation states during HER and OER. The interaction between the catalysts and ionomers and the effect of the electrolyte has been investigated, both of which are of great interest for improving the activity and durability of AEM electrolyzers. The work involved the fabrication of membrane electrode assemblies (MEAs) and single-cell AEM electrolyzer testing. A key result of this work is the achievement of a state-of-the-art performance of 1.15 A/cm2 at 2 V in full non-PGM electrolyzer of Ni-MoO2 (3 mg/cm2) at the cathode and Ni0.6 Co0.2 Fe0.2 (5 mg/cm2) at the anode at 50 oC in 1M KOH with superior stability for 65 hours at 0.5 A/cm2 in 0.1 M KOH. | en_US |
