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

Abstract

The photocatalytic generation of hydrogen peroxide from water and dioxygen (H2O + 1/2O2 → H2O2, ΔG° = +117 kJ mol-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 (~523 K) 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 π-conjugated and π-stacked benzenoid-quinoid donor-acceptor resorcinol units. The acidic conditions result in the resins with a lower bandgap (1.7 eV) and higher conductivity because the lower degree of crosslinking creates a strongly π-stacked architecture. The irradiation of the RF-acid resins with simulated sunlight in water with atmospheric-pressure O2 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.

Mechanistic analysis of multiple processes controlling solar-driven H2O2 synthesis using engineered polymeric carbon nitride

“…Mesoporous carbon nitride (mpg-C 3 N 4 ), which is an efficient photocatalyst for H 2 evolution 56 , shows low performance in the selective 2e − ORR, producing only 0.53 mM H 2 O 2 . As the H 2 O 2 production reaction involves transfer of protons as well as electrons, the acidic media is normally more favorable 15 – 17 . However, PCN-NaCA-2 favors neutral to mild basic conditions for efficient solar-driven H 2 O 2 production (Fig.…”

Photosynthesis of hydrogen peroxide in water: a promising on-site strategy for water remediation

“…Acid-catalysis for the synthesis of RF resins is another method to alleviate the resistance of methylene linkers. 72 Acid-triggered polycondensation produces RF resins with a low degree of crosslinking and a high structural flexibility, resulting in an enhanced π-stacking interaction between or within the polymer chains, of which the band gap decreases with the increase of conductivity (Fig. 6g).…”

Photocatalytic H 2 O‐to‐H 2 O 2 and ‐H 2 affected by Pd‐TiO 2‐δ /TiO 2

“…where the total input energy: 0.625 mW/cm 2 , 4H H2O2 : 117 kJ/mol, and 4H H2 : 237 kJ/mol. The apparent quantum yield (AQY) of the Pd-TiO 2-δ / TiO 2 for the photocatalytic H 2 generation was calculated using the following equation 46 :…”

“…The conversion efficiencies SE H2O2 and SE H2 for photocatalytic H 2 O-to-H 2 O 2 and -H 2 were also calculated using the following equations 46 :…”