Photocatalytic H2O-to-H2O2 by BiOI/g-C3N4/CoP S-scheme heterojunctions

Photocatalytic H2O-to-H2(g) and -H2O2(aq) (2H2O(l) →H2(g) + H2O2(aq)) through a two-electron reaction is kinetically feasible. The proton-coupled two-electron transfer induced photocatalytic oxygen reduction reaction (ORR) from oxygen and water is also an accessible path for a safe production of H2O2. It is thus desirable to synthesize effective photocatalysts that yield H2O2 through the coupling of two-electron transfer water oxidation (+1.23 VNHE) and ORR (+0.68 VNHE). In this work, new g-C3N4/BiOI S-scheme heterojunctions with co-catslyst CoP (BiOI/g-C3N4/CoP) were prepared for the photocatalytic H2O-to-H2O2 reactions. The BiOI/g-C3N4/CoP heterojunctions can enhance visible-light absorption and reduce electron-hole pair recombination rates. Through the water splitting by two-electron and reduction of oxygen, the BiOI/g-C3N4/CoP heterojunctions have a better photocatalytic H2O-to-H2O2 yield than the BiOI/g-C3N4 heterojunction by 3.0-8.4 times. With more CoP (i.e., 19 wt%) on the BiOI/g-C3N4, the BiOI/g-C3N4/(CoP)0.19 heterojunction generates more photocatalytic H2O2 with a higher formation rate constant (kf), equilbrium constant (K) and lower decomposition rate constant (kd). This new, low-cost and ready-prepared BiOI/g-C3N4/CoP S-scheme heterojunction has a high efficiency for the reversible photocatalytic H2O-to-H2O2 reaction, which shows a feasibility for applications in H2O2-fuel cells for electricity using the solar energy.

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