High‐Rate CO 2 ‐to‐CH 4 Photoreduction by Dual‐Proton Hydrogenation Pathway Over Pd‐Anchored Oxygen‐Deficient ZnO Nanosheets

Photoreduction of CO₂ into CH₄ usually comprises upto eight proton-coupled electron transfer steps, greatly reducing the conversion performance. Here, we report a new dual-proton hydrogenation pathway for CO₂-to-CH₄ 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_O nanosheets as an example, synchrotron-radiation X-ray absorption fine structure spectroscopy discloses the Pd nanoclusters are anchored on the ZnO-V_O 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 CO₂ undergoes stepwise dual-proton hydrogenation routes, gradually transforming into *HCOOH, *HCHO, *CH₃OH, and CH₄, different from the traditional CO₂-COOH-CH₄ processes. Thus, the Pd/ZnO-V_O nanosheets exhibit superior CH₄ evolution rate of 257.6 µmol g^-1 h^-1, outperforming all previously reported photocatalysts. This work unlocks an efficient CO₂-to-CH₄ pathway, largely reducing the number of reaction steps.