Enabling novel energy conversion schemes by (1) developing facile and green nanofabrication techniques, (2) designing bioinspired heterogeneous electrocatalysts, (3) constructing efficient and selective hybrid bilayer membrane platforms

Abstract

Electrocatalytic synthesis of feedstocks is envisioned to be a sustainable and green alternative to replace traditional thermal chemical technologies. The objectives of my thesis were to investigate electrochemical resourcification in three facets. First, I devised a facile and green nanofabrication method for water splitting and polyol oxidation. Second, I developed dual-metal atom active site electrocatalysts for oxygen reduction reaction (ORR) as well as evaluated the effect of mechanical interlocking on the ORR activity of molecular Cu complexes. Third, I prepared bio-inspired electrocatalytic platforms to study the proton-coupled electron transfer (PCET) mechanism and control the selectivity of electrooxidation of polyols. In chapter 1, I provided a brief introduction on the current energy conversion situation as well as lay out the limitations and challenges of present technologies. Then I described alternative energy conversion schemes. In chapter 2, I presented general procedures and experimental details including physical and functional characterizations. In chapters 3 to 5, I developed a facile and green nanofabrication technique to prepare platinum (Pt), ruthenium (Ru), and nickel (Ni) nanoparticles for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) as well as bi-metallic palladium-copper (PdCu) nanoparticles for glycerol oxidation reaction (GOR). In chapter 3, I developed a scalable laser-assisted method to produce active and robust graphene-supported nanoparticles as water splitting electrocatalyst. The electrochemical results demonstrated that these binder-free, size-tuneable, few-layer graphene-supported Pt, Ru, and Ni nanoparticles made using the laser-assisted nanomaterials preparation (LANP) strategy can serve as potential electrocatalysts for water-splitting reactions in advanced electrolyser technology. In chapter 4, I presented electrochemical results and product analysis of glycerol oxidation catalyzed by bi-metallic PdCu nanoparticles fabricated using LANP method. Upon optimizing the Pd:Cu ratio, high activity and selectivity were achieved. In chapter 5, I detailed our collaboration project with Dr. Nathalie Herlin-Boime to study early transition metal catalyst containing tantalum/nitrogen/oxygen (Ta/N/O) nanomaterials for H2O2 redox reaction. Electrochemical studies in neutral and alkaline conditions demonstrated that Ta4N5 was the active component for H2O2 oxidation and reduction. In chapter 6, I designed a copper-based dual-atom catalyst for ORR. This bio-inspired non-precious metal (NPM) catalyst exhibits decent ORR onset potential and high selectivity for the 4-electron pathway to generate water (O2 + 4 e– + 4 H+ → 2 H2O). The electrochemical results indicated that the optimized di-copper electrocatalyst broke the ORR onset potential record for all published artificial di-copper catalysts. In chapter 7, I described our collaboration efforts with Dr. Ho Yu Au-Yeung’s group to study the influence of mechanical interlocking on the ORR activity and selectivity of molecular Cu complexes. Catanene was used as a supporting ligand to enforce mechanical interlocking onto the central Cu ion to achieve tuneable ORR efficiency and pathway selectivity. In chapter 8, I designed a new bio-inspired electrocatalytic platform with a widened operating potential window for polyol electrooxidation. The identity of the self-assembled monolayer (SAM) controlled the electron transfer rate while the lipid components of the hybrid bilayer membrane (HBM) regulated the proton transfer rate. By modulating the kinetics and thermodynamics of both electron and proton transfer steps, the product selectivity of polyol electrooxidation was tuned on demand. In chapter 9, I summarized my work and provided an outlook.