Murphy, Frédéric2025-02-132025-02-132025-02-13http://hdl.handle.net/10393/50184https://doi.org/10.20381/ruor-30928The commercialising of green H2 from water electrolysis is expected to play an important role in the decarbonisation of the global economy. While its commerciality has steadily been improved over the decades from breakthroughs in electrocatalyst, separator and cell design, it still is uncompetitive against other forms of energy storage such as natural gas. This challenge is primarily related with the intrinsic equilibrium potential needed to initiate the coupled half-cell reactions of water electrolysis in similar pH which represents the majority of it’s electricity consumption. To contour this, coupling the half cell hydrogen evolution reaction (HER) responsible for producing H2 with a more thermodynamically favourable anodic electrochemical reaction has shown promise. Among the possible oxidation reactions, glycerol electrooxidation (GEOR) has shown a great deal of attention due to its surplus, high functionality allowing for a large window of potential products, significantly low onset potential, reduced risk both in terms of handling and competitive inhibition of O2 production. Most scientific research in GEOR has been focused on its selectivity, reactivity, and resistance to poisonous species due to its significant revenue generation from its value-added products as opposed to H2. Much has been achieved in terms of designing both reactive and selective platinum group and Ni based catalysts. However, the focus on selectivity and general electrochemical tests within small 3-electrode cells has created an under reporting of relevant electrochemical tests within industrially relevant zero-gap electrolysers. This is of particular importance since reporting the advantage of GEOR without its required coupled cathodic reaction to complete the circuit doesn’t provide information to its advantages or limitations from an engineering perspective. In this thesis, previous electrocatalysts developed by Houache et al. 2020 and Asma Shubair et al. 2022 were examined in a relevant 25 cm2 zero-gap electrochemical cell where polarization curves are produced. Additionally, electrolyser parameters such as temperature, catalyst loading, and concentrations are varied due to the lack of studies investigating the influence of external parameters on GEOR in literature. Due to the absence of O2 production, all electrolyser tests were performed with a filter paper to demonstrate the further possibility to reduce the CAPEX significantly as opposed to an anion exchange membrane water electrolysers. The application of a V membrane-free electrolyser also requires an investigation of the influence of glycerol on the hydrogen evolution reaction. Unexpected discoveries were made along the electrolyser tests which did require further investigation. Scaling GEOR to a larger cell not only demonstrated challenges and opportunity to GEOR in terms of energy consumption for H2 production, but it also detected novel GEOR reactions which have not previously been discovered due to difficulties of measuring such phenomena within small 3-electrode cells. Additionally, upscaled polarization curves also demonstrated the detection of a novel GEOR related deactivation mechanism which differs from literature and suggests that catalyst designs for GEOR should consider downstream electrolyte compositional changes to resist deactivation or changes in GEOR mechanism. Finally, investigation of glycerol on the hydrogen evolution reaction has led to a contradiction to the hypothesis in literature. Electrochemical results suggest glycerol acts as both an inhibitor and promoter for HER depending on the catalyst material and the specific HER mechanism in question. DFT and AIMD simulations are recommended to further investigate. However, the differences in catalyst sensitivities to glycerol suggest catalyst designs can mitigate the inhibitory effects of glycerol on HER or even promote HER. Additionally, impedance spectroscopy measurements strongly correlate glycerol interferes with the Nafion® binder microphase structures, significantly inhibiting electrolyte conduction and H2O replenishment which are critical for the hydrogen evolution reaction, highlighting the need for the GEOR field to investigate other ionomers as suitable binders. Furthermore, evidence points to the influence of glycerol on OH- conduction in liquid phase is nulled due to the novel Grothuss conduction mechanism of OH-, presenting a significant advantage for membrane-free electrolysers. Overall, no symmetrical/asymmetrical Ni cell in this work met the D.O.E. target, with the lowest operating at 42.1 kWh.kgH2-1, due to the required metal oxidation state for GEOR to initiate over Ni is intrinsically elevated. Nonetheless, Pd phase GEOR-HER did manage to operate at 37 kWh.kgH2-1, meeting the D.O.E.. This is due to its lower required potential to oxidise potential to an active GEOR state.enAttribution-NonCommercial-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-nd/4.0/electrocatalystelectrolysisorganic electrolysisprocess designconductionglycerolalcoholhydrogen evolution reactionHERglycerol electrooxidationGEORhydroxidePalladiumGoldNickelcarbon supportbulk oxidation stateNafionoperational parameterspolarization curvechronoamperometrygreen hydrogencompetitive adsorptioncatalyst regenerationpromotioninhibitionThesis