Solar-to-hydrogen peroxide energy conversion on resorcinol-formaldehyde resin photocatalysts prepared by acid-catalysed polycondensation

The photocatalytic generation of hydrogen peroxide from water and dioxygen (H2O+1/2O(2)-> H2O2, Delta G degrees=+117kJmol(-1)) under sunlight is a promising strategy for the artificial photosynthesis of a liquid fuel. We had previously found that resorcinol-formaldehyde (RF) resin powders prepared by the base-catalysed high-temperature hydrothermal method act as semiconductor photocatalysts for H2O2 generation. Herein, we report that RF resins prepared by the acid-catalysed high-temperature hydrothermal method (similar to 523K) using common acids at pH < 4 exhibit enhanced photocatalytic activity. The base- and acid-catalysed methods both produce methylene- and methine-bridged resins consisting of -conjugated and pi-stacked benzenoid-quinoid donor-acceptor resorcinol units. The acidic conditions result in the resins with a lower bandgap (1.7eV) and higher conductivity because the lower-degree of crosslinking creates a strongly pi-stacked architecture. The irradiation of the RF-acid resins with simulated sunlight in water with atmospheric-pressure O-2 generates H2O2 at a solar-to-chemical conversion efficiency of 0.7%, which is the highest efficiency ever reported for powder catalysts used in artificial photosynthesis. Low-bandgap polymers hold great potential for photocatalytic generation of hydrogen peroxide, but increasing catalytic activity remains challenging. Here, a solar-to-chemical conversion efficiency of 0.7 % is reached for a resorcinol-formaldehyde resin powder prepared via acid-catalyzed high-temperature hydrothermal synthesis.