RUTHENIUM BASED HETEROGENEOUS CATALYSTS FOR THE HYDROGEN EVOLUTION REACTION IN HIGHLY ACIDIC ELECTROLYTES
Open Access
- Author:
- Seth, Kriti
- Graduate Program:
- Chemistry
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 07, 2019
- Committee Members:
- Raymond Edward Schaak, Thesis Advisor/Co-Advisor
Raymond Edward Schaak, Thesis Advisor/Co-Advisor
Christine Dolan Keating, Committee Member
Miriam Arak Freedman, Committee Member - Keywords:
- Hydrogen Evolution Reaction
Electrocatalysis
Water-Splitting
phosphides
intermetallics - Abstract:
- Replacement of fossil fuels with sustainable and cleaner energy sources is one of the most urgent challenges of this century. Harvesting solar energy to store it in chemical bonds of clean fuels such as hydrogen is one of the most attractive solutions to the global energy crisis. Discovery and development of heterogeneous catalyst materials for devices that facilitate water splitting into hydrogen (hydrogen evolution reaction) and oxygen (oxygen evolution reaction) is central to their large-scale implementation. For the hydrogen evolution reaction (HER) under acidic conditions, Pt is the benchmark heterogeneous catalyst as the optimum strength of a Pt-H bond leads to fast reaction rates and low energy barriers. However, high cost and scarcity inhibits its application in commercial devices, motivating the search for cheaper and more sustainable alternatives. Metal free and non-noble metal alternatives which are more earth abundant that have been developed are still inferior to Pt-based catalysts, with their performance being far from satisfactory. Ruthenium has a relatively lower cost (about 10% of Pt) but possesses similar bond strength with hydrogen as that of Pt. Therefore, ruthenium catalysts, a promising trade-off between activity and cost, have recently started emerging. Now it is imperative to develop highly efficient Ru-based catalyst materials that can facilitate HER with a low mass loading of this noble metal. In this work we synthesize bulk ruthenium-based electrocatalysts via solid-state techniques and evaluate them for the HER in acidic electrolytes. In Chapter 2, we present controllable syntheses of powders as well as single crystals of binary ruthenium phosphides namely Ru2P, RuP and RuP2 as well as ternary lanthanum ruthenium phosphides. On evaluating the HER performance of these in 0.5 M H2SO4, we confirm high HER activity for the three morphologically similar but structurally distinct phases of Ru-P, as well as establish an empirical trend to elucidate the effect Ru: P ratio on activity. In addition, we also investigate single crystals of ternary lanthanum ruthenium phosphides, such as LaRu2P2, made by using tin flux as novel HER catalysts with diluted noble metal content which show high activity and stability. Next, in Chapter 3, we evaluate the HER performance of single crystals of Ru-Sn and Ru-Al intermetallics made using the metal flux in acidic electrolytes. When tested as single crystal electrodes, even though Ru3Sn7 exhibited moderate performance, we obtain excellent activity and long-term stability for Ru4Al13, superior to that of commercial Ru/C catalyst and at par with some of the state-of-the-art Ru based materials. The excellent HER performance of Ru4Al13 makes such intermetallic compounds as viable alternatives to Pt to produce hydrogen via the HER central to solving the global energy crisis.