Ex Situ and In Situ Analyses of the Mechanism of Electrocatalytic Hydrogen Peroxide Production by Co x Zn 1–x O (0 < x < 0.018) Materials in Alkaline Media
Metal oxide semiconductors have attracted much attention due to their versatility in different applications, ranging from biosensing to green energy-harvesting technologies. Among these metal oxides, oxide-based diluted magnetic semiconductors have also been proposed for fuel cell applications, especially for the oxygen reduction reaction (ORR) and the oxygen evolution reaction. However, the catalytic mechanism has been proposed to follow a two-electron pathway, forming hydrogen peroxide, instead of the four-electron pathway. Herein, we report cobalt-doped zinc oxide (CoxZn1–xO, 0 < x < 0.018) materials prepared using a co-precipitation method suitable for the electrocatalytic production of hydrogen peroxide. The electrocatalytic performance of CoxZn1–xO materials showed up to 60% hydrogen peroxide production with onset potentials near 649 mV, followed by the two-electron ORR mechanism. Ex situ X-ray absorption spectroscopy experiments at the Co K-edge demonstrated the presence of Co(II) ions at tetrahedral sites within the ZnO lattice.