Electro-reforming of poly(ethylene glycol) solutions for the production of H2 at low temperature

SSCI-VIDE+CARE+NGO:PVE:ACVNational audienceHydrogen is an essential industrial target area, not only because of its use as an energy carrier and practical employment in fuel cells but also for its role as a significant raw material of the chemical industry [1]. Hydrogen can be produced by different processes (CH4 reforming being the most common), but the electrolysis of water is called to be an environmentally friendly solution. This process has taken force lately because it can be easily integrated to the electrical grid and use renewable energy sources (i.e. solar or wind) to produce pure H2 from water, producing only O2 as a by-product [2]. However, the thermodynamic cell voltage to achieve the water electrolysis reaction is around 1.23 V at room temperature [3]. Consequently, different strategies have been proposed to electrolyze organic molecules instead of water at the anode of low-temperature electrolyzers to reduce the energy demand. Plastic wastes contain an abundant source of hydrogen can be a promising renewable feedstock for electrolysis. A handful of studies have been published on this approach. Among them, our group published two studies considering the electro-reforming of poly(methyl methacrylate) (PMMA) [4,5]. Even if some initial findings demonstrate the proof-of-concept, several limitations were found: accumulation of species at the anode and poisoning. Moreover, the fact of having only C-C bonds in the main PMMA chain complicate considerably hinders the process kinetic. To go further on the understanding of the electrochemical oxidation of polymeric materials, we investigated the electro-oxidation of poly(ethylene glycol) (PEG) in a Proton Exchange Membrane (PEM) reactor. The system was initially studied using ethylene glycol on state-of-the-art electrodes. The anode formulation and morphology were optimized for its application to these organic macromolecules. The impact of temperature (30-80 °C), polymer concentration (1-20 g L-1) and molecular weight (200-4000 g mol-1) on the performance of the system was investigated. It was found that PEG can be electro-oxidized following two main routes involving weakly adsorbed or strongly chemisorbed species. Moreover, the production and purity of hydrogen in the cathode compartment was verified by an on-line mass spectrometer (Figure 1a), with a faradaic efficiency of 99.75%. The size of the macromolecules decreased after a chrono-amperometry experiment, as confirmed by steric exclusion chromatography (SEC) (Figure 1b), demonstrating the partial electro-oxidation of polymers containing C-O bonds in their main chain. The application of this concept for the production of hydrogen by electrochemical means seems promising, but further research in this field is necessary