Electrocatalytic production of glycolic acid via oxalic acid reduction on titania debris supported on a TiO2 nanotube array

Electrodes prepared by anodic oxidation of Ti foils are robust and not toxic materials for the electrocatalytic reduction of oxalic acid to glycolic acid, allowing the development of a renewable energy-driven process for producing an alcoholic compound from an organic acid at low potential and room temperature. Coupled with the electrochemical synthesis of the oxalic acid from CO2, this process represents a new green and low-carbon path to produce added value chemicals from CO2. Various electrodes prepared by anodic oxidation of Ti foils were investigated. They were characterized by the presence of a TiO2 nanotube array together with the presence of small patches, debris, or TiO2 nanoparticles. The concentration of oxygen vacancies, the amount of Ti3+ measured by X-ray photoelectron spectroscopy (XPS) and the intensity of the anodic peak measured by cyclic voltammetry, were positively correlated with the achieved oxalic acid conversion and glycolic acid yield. The analysis of the results indicates the presence of small amorphous TiO2 nanoparticles (or surface patches or debris) interacting with TiO2 nanotubes, the sites responsible for the conversion of oxalic acid and glycolic acid yield. By varying this structural characteristic of the electrodes, it is possible to tune the glycolic acid to glyoxylic acid relative ratio. A best cumulative Faradaic efficiency (FE) of about 84% with FE to glycolic acid around 60% and oxalic conversion about 30% was observed.