Designing electrocatalysts with high activity, selectivity, and stability for the two-electron water oxidation reaction (2e– WOR) to produce H2O2 remains challenging. Although many single-component electrocatalysts have been investigated, their performance has plateaued. Here, we demonstrate an effective strategy for transforming an inert metal oxide such as rutile TiO2 into an active electrocatalyst by supporting it with a metallic layer that incorporates very mobile charge carriers. Experimentally, we show that a Pt support layer dramatically enhances the performance of TiO2, yielding higher current densities, lower onset potentials, and markedly improved Faradaic efficiency for producing H2O2. Our density functional theory calculations reveal the mechanistic origin of this enhancement, which lies in the presence of free-electron charge carriers on the support required for 2e– WOR. As a result, the Pt support causes the crucial OH* intermediate to bind more tightly to the active site than Pt-free TiO2, leading to improved activity and selectivity of thin TiO2(110) overlayers for producing H2O2. Through a comparative analysis with a nonenhancing Ag support via examination of the density of states, we pinpoint the electronic cause as the hybridization between Ti 3d and Pt 5d orbitals, which creates available 5d-band electrons near the Fermi level. This 5d-band availability and higher work function difference allow for a more favorable charge transfer to the OH* reaction intermediate. Our findings establish the electronic character of the buried support as a key design parameter for creating highly active and selective heterostructure catalysts for H2O2 synthesis.