ZnO@Cryptomelane‐Type MnO ₂ Heterostructures for High‐Efficiency Photocatalytic CO ₂ Reduction: Synergistic Charge Transfer and Reaction Pathway Elucidation

ABSTRACT The development of efficient photocatalysts for CO 2 reduction is pivotal to meet global energy demands and mitigate environmental degradation. In this study, we designed ZnO@cryptomelane‐type MnO 2 (ZnO@Cry) heterostructures via a facile in situ growth strategy, achieving remarkable visible‐light‐driven CO 2 ‐to‐CO conversion. The 0.3‐ZnO@Cry composite sample obtained by optimizing the ZnO loading demonstrated superior photocatalytic performance, achieving a CO production rate of 88.53 μmol·g −1 ·h −1 (3.9‐ and 19.5‐fold higher than pristine Cry and ZnO, respectively) with 96.8% selectivity and minor CH 4 formation (2.68 μmol·g −1 ·h −1 ). Structural and mechanistic analyses revealed that the integration of ZnO nanosheets into Cry nanowhiskers established an interfacial heterojunction, enhancing visible light absorption and charge separation efficiency. X‐ray photoelectron spectroscopy and CO 2 temperature‐programmed‐desorption studies confirmed that 0.3‐ZnO@Cry had the highest Mn 3+ /Mn 4+ ratio, which synergistically promoted CO 2 adsorption/activation and intermediate stabilization. Transient photocurrent and electrochemical impedance spectroscopy measurements further validated the accelerated electron transfer and suppressed recombination kinetics in the heterostructure. In situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) elucidated the reaction pathway, wherein CO 2 was sequentially reduced to and intermediates, ultimately desorbing CO, whereas minor CH 4 formation proceeded via hydrogenation. Remarkably, the catalyst retained more than 95% of its activity over five cycles, indicating robust stability. This study highlights the critical roles of heterojunction engineering and defect modulation in advancing solar‐driven CO 2 valorization, thereby offering a sustainable blueprint for carbon‐neutral technologies.