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

Abstract Photoreduction of CO 2 into CH 4 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 2 ‐to‐CH 4 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 CO 2 undergoes stepwise dual‐proton hydrogenation routes, gradually transforming into *HCOOH, *HCHO, *CH 3 OH, and CH 4 , different from the traditional CO 2 ‐COOH‐CH 4 processes. Thus, the Pd/ZnO‐ V O nanosheets exhibit superior CH 4 evolution rate of 257.6 µmol g −1 h −1 , outperforming all previously reported photocatalysts. This work unlocks an efficient CO 2 ‐to‐CH 4 pathway, largely reducing the number of reaction steps.