Electrochemical conversion of furfural to furoic acid: a more stable, efficient and energy-saving system

The paired electrolytic system is constructed by combining the valuable organic electro-oxidation and electro-reduction reactions, which can replace the ineffective water splitting half-reaction. By reducing the energy consumption of the electrolytic cell, the value-added electrolysis is realized. The indirect electrolysis method greatly reduces the dependence of the organic electrolysis reaction on electrode potential by introducing the redox mediators, which solves the problem on the matching of anode and cathode current under potentiostatic conditions. Here, we report a more stable, efficient and energy-saving linear paired electrochemical synthesis system that can simultaneously convert furfural to furoic acid at both the anode and cathode at higher current densities. Stable three-dimensional networked PbO2 is used as the anode and the catalytic amount of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) is used as the mediator to realize the efficient conversion of furfural to furoic acid in a wide potential range. The cathode catalyzes two-electron oxygen reduction to hydrogen peroxide using Pb/RHPC gas-diffusion electrode, which mediates the oxidation of furfural to furoic acid simultaneously. In potentiostatic electrolysis, the selectivity of the furoic acid in the cathode and anode is 33.2% and 99.3%, respectively, and the total electron efficiency is 127.1%. The properties of the cathode and anode remain stable after the long-time electrolysis in a flow cell. By choosing a stable anode with high oxygen evolution overpotential and a gas-diffusion cathode with high hydrogen evolution overpotential, the electrolytic cell can be operated efficiently and stably by introducing reasonable mediated reactions. The two half-reactions have good compatibility during the electrolysis process, saving energy consumption by about 12.3%, for certain industrial application prospects.