Tuning oxygen molecule passivation and transfer on the catalyst surface for highly efficient hydrogen evolution from formaldehyde.

In hydrogen evolution reactions (HER), hydrogen-oxygen recombination reaction typically reduces the hydrogen generation rate. However, in the HER from formaldehyde, un-dissociated oxygen molecules can promote hydrogen generation. In this paper, a series of PdZn/g-C3N4 alloy catalysts were synthesized, and by varying the catalyst composition successfully regulated the reactive sites and surface-interface behaviors, thus enhancing the HER rate. Under optimal conditions (1.5 M NaOH, 2.0 M HCHO, Pd1Zn1/g-C3N4), the Pd1Zn1 alloy catalyst exhibits the highest catalytic activity for hydrogen evolution reaction, with a hydrogen evolution rate of 422.86 μmol·h-1. Mechanistic study of hydrogen production from formaldehyde revealed that O2 molecules are converted into reactive oxygen species HOO-, which then react with formaldehyde to produce hydrogen. The adsorption energies of formaldehyde and oxygen molecules, as well as the O2 dissociation energy barrier, vary significantly with the PdZn alloy compositions, affecting O2 chemical behavior, impeding O2 dissociation, and accelerating the transfer of active species. The results of theoretical calculations indicate that on the surface of the Pd1Zn1/g-C3N4 alloy catalyst, oxygen molecules possess an appropriate adsorption energy and a relatively high dissociation energy barrier. This is conducive to the formation of oxygen-containing active species. Meanwhile, the coordination between metal atoms promotes the efficient transfer of photogenerated electrons and prolongs the photoelectron lifetime. Thus, adjusting the PdZn alloy composition can effectively regulate and enhance the catalyst's hydrogen production activity.