CO2-free electric power circulation via direct charge and discharge using the glycolic acid/oxalic acid redox couple†
The establishment of an efficient electric power distribution method is the key to realising a sustainable society driven by renewable-energy-based electricity, such as solar photovoltaics, wind turbine, and wave electricity, in view of supply instability. Here, we demonstrate an electric power circulation method that does not emit CO2 and is based on the glycolic acid (GC)/oxalic acid (OX) redox couple. Direct electric power storage in GC ensures considerably high energy density storage and good transportability through OX electroreduction with significantly high selectivity (>98%) using pure anatase-type titania (TiO2) spheres under mild conditions in the potential region of −0.5 to −0.7 V vs. the RHE at 50 °C. The most desirable characteristic of this electroreduction is the suppression of hydrogen evolution even in acidic aqueous media (Faraday efficiency of 70–95%, pH 2.1). We also successfully generated power without CO2 emissions via selective electrooxidation of GC with an alkaline fuel cell.