Alanine Formation in a Zero-Gap Flow Cell and the Role of TiO₂/Ti Electrocatalysts

The electrochemical synthesis of $$ -amino acids at room temperature and pressure is a sustainable alternative to conventional methods like microbial fermentation and Strecker synthesis. A custom-built zero-gap flow electrolyzer was used to study the electrosynthesis of alanine via the electrocatalytic reductive amination (ERA) of the corresponding biomass-derivable $$ -keto acid precursor - pyruvic acid (PA), and hydroxylamine (NH₂OH) at very low pH. Non-toxic, abundant, and easy to prepare TiO₂/Ti electrocatalysts were utilized as the cathode. Three TiO₂/Ti felt electrodes with different oxide thicknesses were prepared and their characterization results were correlated with their respective electrochemical performance in terms of Faradaic efficiency $$ , and partial current density $$ . Cyclic voltammetry indicated a different electrocatalytic reduction process on hydrothermally treated electrodes, compared to thermally oxidized ones. Hydrothermally treated electrodes were also found to have the thickest porous anatase layer and achieved 50-75 % alanine conversion efficiencies. Optimization showed that the cell potential, reactant flow rate and the PA: NH₂OH ratio were crucial parameters in determining the conversion efficiency. $$ and $$ were found to significantly decrease when an excess of is used and, an optimal alanine $$ of 75 % was achieved at 2.0 V applied cell potential and 10 mL/h reactant flow rate.