Development of an integrated photoelectrochemical device for hydrogen evolution and waste valorization

Glycerol, a small organic molecule with the chemical formula C3H8O3, is generated as a byproduct at approximately 10 wt% during biodiesel production. Although glycerol is intrinsically a useful chemical, oversupply has significantly depressed its market price, and improper disposal can cause environmental harm. As a result, glycerol is often treated as a low-value waste biomass. Importantly, glycerol can be upgraded via electrochemical oxidation into higher-value chemicals such as dihydroxyacetone (DHA) and glyceraldehyde (GLAD). Therefore, the photoelectrochemical (PEC) valorization of glycerol represents a promising approach for transforming a low-value waste stream into value-added products. Moreover, hydrogen is simultaneously generated at the cathode during PEC glycerol oxidation, making the process doubly beneficial. This thesis aims to design and develop a PEC device capable of achieving glycerol upgrading and hydrogen production simultaneously. Electrolytes constitute one of the most critical components in PEC operation, and this thesis first investigates the influence of various supporting electrolytes on the PEC glycerol oxidation performance of BiVO4 photoanodes. By evaluating photocurrent density, photocurrent stability, and the material stability of BiVO4, NaNO3 is identified as the most effective electrolyte. The electrolyte-dependent variations in glycerol oxidation activity are interpreted primarily in terms of how electrolyte ions influence glycerol adsorption on the BiVO4 surface, with the behavior of anions explained using the Hofmeister series. Selectivity is another crucial factor in glycerol oxidation research, as the oxidation products vary widely in economic value. DHA and GLAD, for example, are substantially more valuable than glycerol itself, whereas formic acid is often less economically attractive than refined glycerol. Accurate product analysis is therefore essential, and high-performance liquid 2 chromatography (HPLC) is among the most widely used analytical tools. However, peak overlap—particularly among glycerol, DHA, and formic acid—has long posed a major challenge. As the second contribution of this thesis, an algebraic method is developed to resolve peak-overlap issues encountered during HPLC analysis of glycerol oxidation products. By exploiting the linearity of HPLC chromatograms, it is demonstrated that when n chromatograms are obtained using n detectors with different sensitivities, the concentrations of n products can be determined with small errors even when their peaks completely overlap. Third, a side-by-side PEC device for simultaneous glycerol oxidation and hydrogen production is designed and optimized using multiphysics simulations. Fluid-flow fields are calculated as a function of glycerol concentration and flow rate, and a bridge structure connecting the anolyte and catholyte compartments is devised to prevent product crossover. The voltage loss associated with this bridge is quantified, and simulations show that increasing the bridge cross-sectional area while reducing its length effectively minimizes ohmic resistance. Finally, the thesis is summarized, and an outlook on future directions for glycerol valorization research is provided.