High‐rate CO2‐to‐CH4 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‐VO nanosheets as an example, synchrotron‐radiation X‐ray absorption fine structure spectroscopy discloses the Pd nanoclusters are anchored on the ZnO‐VO 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‐VO 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.