Earth Abundant Catalysts For Alkaline Hydrogen And Oxygen Electrochemistry

The worldwide chemical industry makes extensive use of H2 as a fuel and feedstock. However, most hydrogen production occurs through natural gas, fossil fuels, or coal as a primary source. For the environmental sustainability of hydrogen production, it is necessary to replace these sources with new approaches based on renewable resources, such as solar-driven water electrolysis. Alkaline anion exchange membrane electrolyzers are an attractive technological target to meet the cost target of $2/kgH2 set by the U.S. Department of Energy (DOE). These electrolyzers facilitate the use of non-precious catalysts for the hydrogen evolution and oxygen evolution half-reactions, resulting in significant reductions in capital cost. This dissertation focuses on using Ni-Mo alloy catalysts for hydrogen evolution and oxidation reactions and NiFeOx catalyst for oxygen evolution. We have clarified the nanoscale composition of a previously reported Ni-Mo alloy nanocatalyst by showing that it consists of a core@shell structure where the core is rich in Ni and the shell is predominantly Mo-rich oxides. The structural evolution of core@shell geometry was monitored using in situ transmission electron microscopy, and methodologies were developed to study the metal/metal-oxide interfaces. Based on this compositional insight, we have also determined that unsupported Ni-Mo catalysts suffer from significant conductivity (i.e., electronic transport) limitations, which we have successfully mitigated via the use of carbon supports. The intrinsic activity of these catalysts obtained after carbon incorporation for hydrogen evolution and oxidation reactions was also analyzed. The results suggest that the catalytic activity exhibited by them is within an order of magnitude of the benchmark catalysts but are thousand times cheaper and are therefore very promising. We have extended these studies to NiFeOx catalysts for the oxygen evolution reaction and generated core@shell morphologies by electrochemical activation of binary Ni-Fe alloy nanoparticles supported on oxidized Vulcan carbon. Interestingly, we observed that the activity of these composites systematically increased when the catalyst spent more time in the solution comprising Nafion and isopropyl alcohol. Overall, we have reduced the gap in activity and stability between non-precious and precious metal catalysts for alkaline hydrogen and oxygen electrochemistry