Selected transition metal borides and silicides for the oxygen evolution reaction

In this work, iron and nickel borides and silicides were investigated as catalysts for the oxygen evolution reaction. The compounds investigated include the phase-pure borides FeB, Fe${}_2$B, Ni${}_2$B and Ni${}_3$B as well as the silicides Ni${}_2$Si, Ni${}_{31}$Si${}_{12}$, FeSi, Fe${}_5$Si${}_3$ and Fe${}_3$Si. In addition, solid solution series could be produced for some systems. Thus, the solid solutions (Ni${}_{1-x}$Fe${}_x$)${}_2$B and (Co${}_{1-x}$Fe${}_x$)${}_2$B in the range 0 ≥ x ≥ 1, and (Ni${}_{1-x}$Fe${}_x$)${}_{31}$Si${}_{12}$ and (Fe${}_{1-x}$M${}_x$)${}_3$Si (M=Co, Mn, Ni) in the range 0 ≥ x ≥ 0.5 could be prepared. A direct comparison of the silicides with the borides showed that the majority of the silicides exhibited a significantly higher overvoltage and were thus catalytically less active than the borides. Nevertheless, individual silicides also showed very promising results. It could be shown for the first time on silicides that the overvoltage could be lowered by substitution of the metal and the OER activity could thus be increased. In the case of both silicides and borides, samples containing nickel in particular stand out due to their high catalytic activity. In addition to powdered samples, (Ni${}_{1-x}$Fe${}_x$)${}_2$B compacts (0 ≥ x ≥ 0.5; x = 1) were measured and characterised by XPS before and after the electrochemical investigation. In summary, this work confirmed that both selected silicides and borides are promising candidates for use as OER catalysts and can be significantly optimised, particularly by substitution with transition metals.