2025 Theses Doctoral

Catalytic Production and Utilization of Green Hydrogen for the Conversion of Carbon-Containing Molecules

Turaczy, Kevin Kristian

Given the current policies in place, the world is not on track to achieve net-zero emissions by the year 2050 as greenhouse gas (GHG) emissions continue to rise. Though fossil fuels are heavily linked to GHG emissions, they are a staple in both energy applications and chemical production. Reducing the barriers associated with producing fossil fuel alternatives, such as hydrogen (H₂), will allow society to shift towards net-zero emissions and mitigate anthropogenic driven climate change. At present the majority of H₂ is produced from fossil fuels, making H₂ production from water electrolysis (green H₂), which can be GHG emissions free, an attractive solution. This dissertation studies alternative electrocatalysts for the production of green H₂ that traditionally rely on materials that are scarce, expensive, and associated with relatively large GHG emissions. Furthermore, this work explores applications where green H₂ can be impactful in reducing GHG emissions such as in the upcycling of polyethylene and in the sequestration of biogas into useful solid materials.

First, Pt- and Pd-modified molybdenum nitride (Mo₂N) was explored as an alternative for the traditional Pt electrocatalyst in the hydrogen evolution reaction (HER) for water electrolysis. Hydrogen binding energy (HBE) has been used as a descriptor for potential electrocatalysts and in Chapter 3, the HBE of both Pt- and Pd-modified Mo2N was determined experimentally using temperature-programmed desorption (TPD). This was then correlated with electrochemical measurements in both acidic and alkaline electrolyte. The established trend revealed that the similar activity of Pt/Mo2N, in both media, to Pt(111) is linked to their similar HBE values. Density functional theory (DFT) calculations further verified the trends established in this chapter and provided insight into the electronic structure of these modified Mo₂N surfaces. In Chapter 4, the binding strength of two more Pt-modified transition metal nitride (TMN) surfaces, titanium nitride and vanadium nitride, were explored for their potential use as electrocatalysts in green H₂ production. The desorption of H₂O from Pt-modified titanium nitride and tantalum nitride were also studied to understand their binding affinity to H₂O, which is an important factor in alkaline HER.

Second, the tunability of the product distribution for polymer upcycling was investigated in Chapter 5. Low-density polyethylene (LDPE) was converted using H₂, via hydrogenolysis, into smaller hydrocarbon products with bimetallic RuM₃/CeO₂ (M = Fe, Ni, Co) catalysts. The formation of bimetallic alloys resulted in a shift in product distribution, away from unwanted methane (CH₄) and towards longer chain, value-added products. X-ray absorption fine structure measurements, electron microscopy imaging, and H₂ temperature-programmed reduction were used to characterize the catalysts. Furthermore, n-hexadecane was included as a model compound for polyolefins to determine the effects of H₂ pressure and reaction time on the product distribution. Of the three bimetallic catalysts, RuCo₃/CeO₂ was the most promising and was capable of suppressing C-C bond scission of shorter chain alkanes into CH₄.

Lastly, Chapter 6 reports the successful conversion of biogas (CH₄ and CO₂) into syngas (CO and H₂ followed by carbon nanofiber (CNF) formation using a tandem reactor. This work combined a non-thermal plasma reactor, which can be easily integrated with renewable electricity, for the breakdown of biogas and a thermal reactor, operating at relatively mild temperatures (450 °C), to convert syngas into CNF. Different parameters were varied to determine their impact on CNF formation and biogas conversion. Higher residence times, which were achieved using lower total flow rates and longer plasma lengths, resulted in more CNF growth compared to lower residence times. The production of C₂ and C₃ alkanes and alkenes were also reported as side products from the plasma-assisted conversion of biogas. Chapter 7 highlighted future applications of TPD and non-thermal plasma in H₃ production and utilization as well as suggestions for improving the work presented in this dissertation.