Full-path analysis of HCHO hydrogen evolution breaking O2 limitation: precise synergistic regulation of O2 passivation and C-H bond activation over PdCu/CdS catalysts

Hydrogen production from formaldehyde can overcome the anaerobic limitation of traditional hydrogen production. However, the current mechanism of oxygen-promoted formaldehyde hydrogen production is not universal. The synergistic effect between C-H bond activation and oxygen adsorption-dissociation on catalysts is still unclear, which limits the improvement of hydrogen production performance. In this work, a series of PdCu/CdS alloy catalysts with different Pd/Cu molar ratios were synthesized by an in-situ photodeposition method and used for visible-light-driven oxygen-promoted formaldehyde hydrogen production. Systematic characterizations and theoretical calculations were carried out to study the catalyst structure, photoelectrochemical properties, oxygen-promoted mechanism, on hydrogen production performance. The results show that the formation of Pd-Cu alloy leads to lattice contraction and interfacial electron transfer, which effectively optimize the adsorption and activation of HCHO and O2. The Pd1Cu1/CdS catalyst exhibits the best hydrogen production performance. At room temperature under visible light irradiation, the hydrogen evolution rate reaches 358 μmol·h-1 with good cycling stability. Mechanism studies confirm that O2 molecules insert into the C-H bond of HCHO to form intermediates, and hydrogen comes from the cleavage of C-H bonds that are not attacked by oxygen. The high activity of Pd1Cu1/CdS is mainly attributed to the efficient activation of formaldehyde C-H bonds, moderate adsorption and inhibited dissociation of oxygen, and enhanced charge transfer. This work reveals the molecular mechanism of oxygen-promoted formaldehyde hydrogen evolution, emphasizes the synergistic role of PdCu alloys, and provides theoretical support for developing high-performance formaldehyde hydrogen evolution catalysts.