Surface Functionalized Medium Entropy Alloys for Electrochemical Hydrogen Production

A Doctor of Philosophy Dissertation in Materials Science and Engineering by Shahbaz Ahmad entitled, “Surface Functionalized Medium Entropy Alloys for Electrochemical Hydrogen Production”, submitted in October 2024. Dissertation advisors are Dr. Mehmet Egilmez and Dr. Ali S. Alnaser. Soft copy is available (Dissertation, Completion Certificate, Approval Signatures, and AUS Archives Consent Form).

Abstract

This thesis explores non-precious metal-based electrocatalysts, focusing on medium and high entropy alloys (HEAs) like CoCrNi, CoNiV, and CoNi(Cr/V) for the hydrogen and oxygen evolution reactions (HER and OER). These multi-principal element alloys utilize cost-effective transition metals, known for their robustness, corrosion resistance, and structural stability, and are systematically synthesized and characterized here. Analysis confirmed a stable, single-phase face-centered cubic (FCC) crystal structure in these alloys, while electrochemical testing showed that CoNi(Cr/V) achieved a notable overpotential of 50 mV at 10 mA/cm² and a Tafel slope of 48 mV/dec, highlighting its excellent catalytic performance for HER. To expand on this work, equiatomic thin films of NiCoCr, NiCoV, and NiCo(Cr/V) were created via magnetron sputtering. As bifunctional electrocatalysts, these films exhibited remarkable activity for alkaline water splitting, with the NiCo(Cr/V) film performing comparably to platinum-based catalysts (Pt/C) and showing resilience in both acidic and alkaline conditions. These properties make the NiCo(Cr/V) system a promising candidate for sustainable energy applications. Further, laser structuring applied to NiCo(Cr/V) thin films enhanced the electrochemical performance, with the laser-structured LS-NiCo(Cr/V) samples showing improved HER and OER metrics compared to unstructured samples. This finding highlights the value of laser processing in refining both surface properties and electrocatalytic function in medium entropy alloys.In summary, this research showcases the potential of multi-principal element alloys and surface structuring methods for cost-effective, high-performance electrocatalysts in water splitting applications. These innovations enhance the understanding of electrocatalytic mechanisms and pave the way for practical, sustainable hydrogen production solutions, supporting a shift toward cleaner and economically viable energy systems.