The promoting effect of tetravalent cerium on the oxygen evolution activity of copper oxide catalysts

A new catalyst is presented for the oxygen evolution reaction (OER) based on cerium-modified copper oxide (CuO_x) prepared using a facile electrodeposition procedure. Incorporation of Ce into CuO_x leads to greatly improved OER activity, which reached an optimal value at a surface concentration of 6.9 at% Ce. Specifically, the OER current density at 400 mV overpotential for the most active Ce-modified CuO_x catalyst (6.9 at% Ce) was 3.3 times greater compared to the pure CuO_x. Coincident with the improved OER activity, Ce incorporation also leads to significant structural changes that manifested in increasing degrees of disorder. A further increase in the Ce concentration led to a decrease in the OER performance which can be attributed to the formation of a segregated CeO₂ phase. A strong correlation was observed between the OER performance and tetravalent Ce (Ce⁴⁺) ion concentration, up to a concentration corresponding to CeO₂ phase segregation. No particular trend was observed for the OER activity of these Ce-modified CuO_x catalysts with respect to the surface concentration of Cu ions, surface oxygen species or catalyst structure. The stability of these CuO_x catalysts at 5 mA cm^-2 was also improved with Ce incorporation, and the overpotential required to sustain this current density is much lower than that of pure CuO_x. Overall, this study provides new insights regarding the promoting effect of tetravalent Ce ions on the OER activity of CuO_x-based OER catalysts in alkaline electrolytes.