Electrochemical reduction of carbon dioxide on titanium diboride

Abstract

The electrochemical reduction of carbon dioxide has been studied on metal or surface-modified metal cathodes and semiconductor photocathodes [l-7]. The reaction pathway and the efficiency strongly depend on the electrode material [2,4]. The reduction of carbon dioxide results from the addition of hydrogen followed by the subtraction of the oxygen atom. The electrode surface must be hydrogen-rich to function as a hydrogen source, and parly oxidizable to function as an oxygen sink and to allow the adsorption of carbon dioxide molecules. Titanium, platinum and nickel electrodes show a strong affinity for hydrogen atoms [Sl. However, previous studies on the electrochemical reduction of carbon dioxide on these electrodes in aqueous media have revealed that the major product is hydrogen and the efficiency of the carbon dioxide reduction is low [2,4]. This low efficiency results from either poor adsorption of carbon dioxide or an adsorption state unfavorable for succeeding steps. Inclusion of a second element in the electrode material may improve surface properties. Boron is a promising candidate for the second element; it can form B-O and B-C bonds [9] that serve to accumulate carbon dioxide on the surface, and metal borides provide a variety in stoichiometry [9] that increases the chance for the partial oxidation by carbon dioxide for the oxygen subtraction. This preliminary note is concerned with the properties of a titanium diboride (TiB,) cathode in the electrochemical reduction of carbon dioxide. Titanium diboride is an electroconductive ceramic and an atomically homogeneous mixture of titanium and boron.