Mesoporous curvature-induced proton coupled electron transfer for rapid photoredox of CO2 to CH4

Abstract

The photoreduction of CO 2 is usually terminated by two-electron processes resulting in predominantly products CO, the formulation of eight-electron products CH 4 still remains a great challenge limited by proton coupled electron transfer (PCET) abilities. Here, a novel type of two-dimensional (2-D) mesoporous TiO 2 (mTiO 2 ) has been synthesized based on the nanoscale titanium-oxo cluster units for rapid photoredox of CO 2 to CH 4 . In this unique 2-D structure, a mesoporous sheet with ~ 2.7 nm in thickness and several micrometers in size, can be stably formed into uniform hexagonal arrays. The size of the mesopores can be precisely controlled from 8.0 to 18.0 nm by utilizing the amphiphilic di-block copolymer poly(styrene- block -acrylic acid) (PS- b -PAA) micelles with tunable block lengths. With a curvature-governed Ti 3+ density, such mesoporous sheets demonstrate excellent photocatalytic CO 2 reduction capability by accelerating the PCET processes, achieving a record-high CH 4 production rate of 0.49 mmol g − 1 h − 1 with near-unique selectivity up to 99.6% under full-spectrum solar irradiation, without sacrificial reagents and co-catalysts, and the 2-D mTiO 2 can retain their photocatalytic activity after five consecutive cycles. An equivariant geometric deep learning model was constructed to simulate the spin density of mesoporous TiO 2 , with the objective of identifying exposed active sites. Synchrotron X-ray absorption spectroscopy combined with EELS characterizations unambiguously verify that curved mesoporous interfaces induce reduced Ti − O coordination, concentrated oxygen vacancies and abundant low-valent Ti 3+ sites while retaining the anatase crystalline phase. Density functional theory (DFT) calculations confirm that curvature-enriched Ti 3+ sites can accelerate Volmer step and promote preferential hydrogenation to the carbon atom rather than oxygen (0.73 eV vs. 2.05 eV) due to a bent configuration of the Ti − O−Ti linkage. This atomic-scale selectivity suppresses CO formation and drives the reaction exclusively toward CH 4 , establishing a direct link between mesoporous curvature and multi-electron and proton coupling pathways. This work demonstrates that efficient and selective photocatalytic process can be achived by constructing rich Ti 3+ 2-D mesoporous structure via nanocluster assembly.

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