Anodic Degradation of Lignin at Active Transition Metal-based Alloys and Performance-enhanced Anodes

Electrochemical oxidative degradation is one of the most promising methods for generation of phenolic fine chemicals from the renewable feedstock lignin. High selectivity, no reagent waste, as well as cost efficiency are major advantages of this particular process. Application of Ni- and Co-based anode materials led to the best results in respect to product yield and selectivity. Interestingly, repeated use of Ni foam electrodes for electrochemical oxidative degradation resulted in significantly increased yields of vanillin, indicating a modification of the electrode surface. In particular, activation of the electrodes by electrochemical treatment of black liquor enabled an activation which further increased the electrocatalytic activity as well as the yield of the aroma chemical vanillin up to more than 100 % compared to non-activated Ni foam electrodes. Additionally, this activated electrode surface was analyzed via flowing atmospheric pressure afterglow surface desorption mass spectrometry (FAPA-MS). The measurement revealed diaminotoluene as a major compound in this adsorption layer, which indicates that this compound is partly responsible for the activation process. Most likely, electrochemical induced deposition of such an organic surface layer enhances the lipophilicity of the electrode surface and increases the accessibility of relevant structural features of lignin particles to the anodic surface, resulting in a higher yield of the desired degradation product vanillin.