Electrosynthesis of hydrogen peroxide via selective two-electron transfer oxygen reduction or water oxidation reactions offers a cleaner, cost-effective alternative to anthraquinone processes. However, it remains a challenge to achieve high Faradaic efficiencies at elevated current densities. Herein, we report that oxygen-deficient Pr1.0Sr1.0Fe0.75Zn0.25O4-δ perovskite oxides rich of oxygen vacancies can favorably bind the reaction intermediates to facilitate selective and efficient two-electron transfer pathways. These oxides exhibited superior Faradic efficiencies (~99%) for oxygen reduction over a wide potential range (0.05 to 0.45 V versus reversible hydrogen electrode) and current densities surpassing 50 mA cm-2 under high ionic strengths. We further found that the oxides perform a high selectivity (~80%) for two-electron transfer water oxidation reaction at a low overpotential (0.39 V). Lastly, we devised a membrane-free electrolyser employing bifunctional electrocatalysts, achieving a record-high Faradaic efficiency of 163.0% at 2.10 V and 50 mA cm-2. This marks the first report of the concurrent oxygen reduction and water oxidation catalysed by efficient bifunctional oxides in a novel membrane-free electrolyser for scalable hydrogen peroxide electrosynthesis.