Efficient Electrochemical Oxygen Reduction to Hydrogen Peroxide by Transition Metal-Doped Silicate Sr_0.7Na_0.3SiO_3-δ

Electrochemical oxygen reduction in a selective two-electron pathway is an efficient method for onsite production of H₂O₂. State of the art noble metal-based catalysts will be prohibitive for widespread applications, and hence earth-abundant oxide-based systems are most desired. Here we report transition metal (Mn, Fe, Ni, Cu)-doped silicates, Sr_0.7Na_0.3SiO_3-δ, as potential electrocatalysts for oxygen reduction to H₂O₂ in alkaline conditions. These novel compounds are isostructural with the parent Sr_0.7Na_0.3SiO_3-δ and crystallize in monoclinic structure with corner-shared SiO₄ groups forming cyclic trimers. The presence of Na stabilizes O vacancies created on doping, and the transition metal ions provide catalytically active sites. Electrochemical parameters estimated from Tafel and Koutechy-Levich plots suggest a two-electron transfer mechanism, indicating peroxide formation. This is confirmed by the rotating ring disc electrode method, and peroxide selectivity and Faradaic efficiency are calculated to be in the range of 65-82% and 50-68%, respectively, in a potential window 0.3 to 0.6 V (vs RHE). Of all the dopants, Ni imparts the maximum selectivity and efficiency as well as highest rate of formation of H₂O₂ at 1.65 μmol s^-1.