1. Introduction

Biodiesel, a clean and non-toxic biofuel, is gaining prominence in Europe, and its market is expected to grow [1]. However, during the process of converting plant oils or animal fats into biodiesel, about 10% of glycerol is produced as a by-product [2]. The excess glycerol production drives the need for new applications for its use [3]. This project aims to upgrade glycerol through electrochemical oxidation, reducing waste in the biofuel sector and yielding valuable products. Among all the glycerol derivatives, lactic acid, in particular, is in high demand within the food and pharmaceutical industries. It has been extensively used as a crucial monomer in the production of polylactic acid for manufacturing bio-based plastic [4]. In an electrolysis system resembling water electrolysis, the glycerol electrolysis couples hydrogen evolution reaction (HER) on the cathode side, while substituting the sluggish water oxidation (>1.23 VRHE) with glycerol electro-oxidation reaction (0.6-0.8 VRHE) on the anode side. This process offers a strategy for generating green hydrogen with lower energy requirement compared to water electrolysis. Simultaneously, it enables the co-production of lactic acid, which offers environmental advantages and economic benefits [5]. However, the challenge in this process is the selective production of lactic acid due to the competing reaction pathways for glycerol oxidation, resulting in producing various oxidation products and an increased separation costs downstream.

2. Materials and Methods

Commercial Pt nanoparticles supported on carbon (60 wt%, Pt/C) were employed to benchmark the reaction in an alkaline environment. Various metal oxide supports, such as aluminium oxides, are introduced to enhance the conversion of dihydroxyacetone to lactic acid. The properties of the aluminas are detailed in the table, including the commercial acidic alumina (Al2O3_A), Al2O3 nano powders (Al2O3_NPs), and basic alumina (Al2O3_B). The catalysts were prepared by spray-coating an ink containing Pt/C, which is mixed with metal oxides, to the surface of a carbon paper (Freudenberg H23), which served as a conductive substrate.

Glycerol electrolysis was conducted via chronopotentiometry and chronoamperometry in the Membrane Electrode Assembly cell at 60°C, coupled with online gas chromatography for hydrogen production detection. Following the electrolysis measurements, the electrolytes were collected and analysed using high-performance liquid chromatography to detect liquid oxidation products.

3. Results and Discussion

The results from chronopotentiometry show a stable performance under constant currents at 100 mA over one hour, with a gradual increase in the cell voltage from 0.6 to 0.9V. The resulting electrolytes were collected and analysed using the HPLC for the liquid products. The measurements were carried out on catalysts materials prepared by mixing Pt/C with different alumina materials. The lactic acid yield on Pt/C reaches around 40% and the lactic acid yield on PtC_Al2O3_NPs and PtC_Al2O3_A can reach 68%. The relevant characterisations of the materials and in-situ techniques will be discussed in the presentation.

4. Conclusion

This study demonstrates the effectiveness of the Pt-based materials for glycerol electro-oxidation at a low potential window in alkaline condition. The glycerol electrolysis enables production of H₂ at lower thermodynamic energy input than water electrolysis, meanwhile, allows the co-production of valuable products such as lactic acid, glycolic acid, glyceric acid, etc. The addition of aluminas with surface acidity promote the production of lactic acid from a yield of 40% on Pt/C to 68% on Pt/Al2O3 with acidic properties.