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.