7) or a one-step two-electron ORR route (eq. 8) through the proton-coupled electron-transfer process, in which the protons are predominantly originating from H2O or organic electron donors. Due to the presence of a four-electron ORR competing reaction (eq. 9) the selectivity of H2O2 formation employing oxygen is often lowered. In addition, because the formation of O2 -not only requires a more negative potential (-0.33 V) than the one-step two-electron route (0.695 V), and may induce multiple unpredictable reactions, the low efficiency of step (7) also limits the H2O2 yield and selectivity. Therefore, the one-step two-electron route is more advantageous. The decomposition of H2O2 in reaction (10) cannot be negated entirely, but the one-step two-electron ORR is thermodynamically more favorable. Thus, the key challenge to photocatalytic H2O2 synthesis is the development of a catalyst that has both high activity and selectivity for two-electron ORR. In that context, the addition of plasmonic Au nanoparticles to TiO2 has previously been shown to increase the H2O2 production rate via this two-electron ORR. This concept can now be further exploited using hybrid plasmonic structures, as explained below.