High-Rate CO-to-CH Photoreduction by Dual-Proton Hydrogenation Pathway Over Pd-Anchored Oxygen-Deficient ZnO Nanosheets.

Photoreduction of CO into CH usually comprises upto eight proton-coupled electron transfer steps, greatly reducing the conversion performance. Here, we report a new dual-proton hydrogenation pathway for CO-to-CH conversion, which can condense every two proton-coupled electron transfer steps into one single step. Also, we pioneer the use of in situ synchrotron-radiation vacuum ultraviolet photoionization mass spectrometry to distinguish the crucial HCOOH from COOH intermediates, overcoming the limitation of in situ Fourier-transform infrared spectroscopy. Taking the synthetic Pd/ZnO-V nanosheets as an example, synchrotron-radiation X-ray absorption fine structure spectroscopy discloses the Pd nanoclusters are anchored on the ZnO-V nanosheets via building Pd─O bonds, while theoretical calculation demonstrates charge accumulation on the interfacial Pd sites. In situ spectroscopic characterizations, labelling experiments, and adsorption energy calculations collectively establish CO undergoes stepwise dual-proton hydrogenation routes, gradually transforming into *HCOOH, *HCHO, *CHOH, and CH, different from the traditional CO-COOH-CH processes. Thus, the Pd/ZnO-V nanosheets exhibit superior CH evolution rate of 257.6 µmol g h, outperforming all previously reported photocatalysts. This work unlocks an efficient CO-to-CH pathway, largely reducing the number of reaction steps.