A zirconium-based metal-organic framework containing boron (UiO-66-B) is prepared, which displays efficient photocatalytic H2O2 production. The H2O2 evolution rate is about 1002 μmol g-1 h-1, much higher than that of most known photocatalysts. Pristine UiO-66 displays a much lower activity (314 μmol g-1 h-1) under the same conditions, suggesting the significant role of boron. Both theoretical calculations and the combined experimental results verify the above conclusion, and the role of boron is ascribed to the following aspects: (1) enhanced O2 adsorption, (2) highly selective proton-coupled two-electron transfer, (3) faster carrier separation and surface charge transfer, and (4) faster generation but slower decomposition rates of H2O2. This work highlights key factors in the two-electron O2 reduction reaction (ORR), presents a deeper understanding of the role of boron in enhancing H2O2 production, and provides a new strategy for designing photocatalysts with excellent H2O2 evolution efficiency.