Dual Enhancement of *CO Binding and *H Supply by Photothermal Heterojunction Nanosheets toward High-Efficiency CO ₂ Methanation

Abstract

Photocatalytic CO 2 methanation presents a sustainable route to mitigate greenhouse effect and advance carbon neutrality. However, the pivotal *CO protonation step to *CHO, essential for CH 4 formation, is kinetically and thermodynamically disfavored over *CO desorption, limiting the overall efficiency. To overcome this limitation, we engineer photothermal-coupled Bi 2 S 3 –SnS 2 heterojunction nanosheets that concurrently enhance *CO binding and *H supply, enabling efficient reduction of CO 2 to CH 4 . Comprehensive characterizations via femtosecond transient absorption spectroscopy, in situ X-ray photoelectron spectroscopy, and theoretical calculations confirm a direct Z-scheme charge transfer mechanism. This mechanism promotes charge accumulation at catalytic sites, strengthening *CO binding and thermodynamically switching the dominant pathway from *CO desorption (+1.00 eV) to *CO protonation (−0.88 eV). Additionally, the favorable valence band alignment in the heterojunction facilitates H 2 O dissociation to produce *H. Crucially, H/D kinetic isotopic effect measurements and in situ Fourier-transform infrared spectroscopy reveal a pronounced photothermal effect within the heterojunction, where light-induced heat accelerates H 2 O dissociation and *H transfer kinetics, thereby enhancing the *H supply for *CO protonation. Consequently, the Bi 2 S 3 –SnS 2 heterojunction nanosheets achieve a remarkable CH 4 production rate of 341.4 μmol g –1 h –1, representing a 23.1-fold enhancement over pristine SnS 2 nanosheets and surpassing reported state-of-the-art photocatalysts. This work establishes a paradigm for utilizing photothermal coupling to regulate reaction pathways and boost the catalytic activity in CO 2 conversion.

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