Carbon-neutral energy cycles using alcohols

Abstract

We demonstrated carbon-neutral (CN) energy circulation using glycolic acid (<b>GC</b>)/oxalic acid (<b>OX</b>) redox couple. Here, we report fundamental studies on both catalyst search for power generation process, i.e. <b>GC</b> oxidation, and elemental steps for fuel generation process, i.e. <b>OX</b> reduction, in CN cycle. The catalytic activity test on various transition metals revealed that Rh, Pd, Ir, and Pt have preferable features as a catalyst for electrochemical oxidation of <b>GC</b>. A carbon-supported Pt catalyst in alkaline conditions exhibited higher activity, durability, and product selectivity for electrooxidation of <b>GC</b> rather than those in acidic media. The kinetic study on <b>OX</b> reduction clearly indicated that <b>OX</b> reduction undergoes successive two-electron reductions to form <b>GC</b>. Furthermore, application of TiO₂ catalysts with large specific area for electrochemical reduction of <b>OX</b> facilitates the selective formation of <b>GC</b>.