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

The electrochemical synthesis of α ${\alpha }$ ‐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 α ${\alpha }$ ‐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 η ${\eta }$ , and partial current density j‾ ${\left|\overline{j}\right|}$. 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. η ${\eta }$ and j‾ ${\left|\overline{j}\right|}$ were found to significantly decrease when an excess of is used and, an optimal alanine η ${\eta }$ of 75 % was achieved at 2.0 V applied cell potential and 10 mL/h reactant flow rate. [ABSTRACT FROM AUTHOR]