Metal-organic framework membranes with single-atomic centers for photocatalytic CO2 and O2 reduction

Abstract

The demand for sustainable energy has motivated the development of artificial photosynthesis. Yet the catalyst and reaction interface designs for directly fixing permanent gases (e.g. CO2, O2, N2) into liquid fuels are still challenged by slow mass transfer and sluggish catalytic kinetics at the gas-liquid-solid boundary. Here, we report that gas-permeable metal-organic framework (MOF) membranes can modify the electronic structures and catalytic properties of metal single-atoms (SAs) to promote the diffusion, activation, and reduction of gas molecules (e.g. CO2, O2) and produce liquid fuels under visible light and mild conditions. With Ir SAs as active centers, the defect-engineered MOF (e.g. activated NH2-UiO-66) particles can reduce CO2 to HCOOH with an apparent quantum efficiency (AQE) of 2.51% at 420 nm on the gas-liquid-solid reaction interface. With promoted gas diffusion at the porous gas-solid interfaces, the gas-permeable SA/MOF membranes can directly convert humid CO2 gas into HCOOH with a near-unity selectivity and a significantly increased AQE of 15.76% at 420 nm. A similar strategy can be applied to the photocatalytic O2-to-H2O2 conversions, suggesting the wide applicability of our catalyst and reaction interface designs.

Insight on Reaction Pathways of Photocatalytic CO2 Conversion

“… 44 The benchmark system for CO 2 photoreduction to formic acid was based on a gas-permeable metal–organic framework (MOF) with an apparent quantum efficiency (AQE) of 15.76% at 420 nm, at the porous gas–solid interfaces with a near-unity selectivity. 68 Such a high quantum efficiency is also the highest among most systems for the C 1 products, suggesting that the metal–organic complexes play a significant role in CO 2 reduction. More examples of metal complex photocatalysts could be found in other reviews.…”

Rational Synthesis and Regulation of Hollow Structural Materials for Electrocatalytic Nitrogen Reduction Reaction

“…[ 189 , 190 ] Atom‐level exposure of SACs makes full use of individual atoms, not only improving quality and yield, but also effectively saving costs, especially for precious metals. At present, SACs have made considerable progress in the field of catalysis, such as oxygen reduction reaction, [ 191 ] carbon dioxide reduction reaction, [ 192 ] oxygen evolution reaction, [ 193 ] HER, [ 194 ] and NRR. [ 195 ] However, their surface energy is high due to the reduced size, making it necessary to find a suitable substrate to anchor them.…”

Support–Activity Relationship in Heterogeneous Catalysis for Biomass Valorization and Fine-Chemicals Production

“…The high surface area generates a very high density of catalytic sites, allowing greater possibilities of contact with substrates and producing catalysts with high activity and excellent steric selectivity, tunable by changing linkers shape and length in the synthesis steps [178]. The range of reactions that can be performed with MOF-based catalysts is almost as wide as their synthetic tunability: industrially relevant reactions involving commodities production (butenes syntheses for synthetic rubber production) [181]; environmental remediation reactions with greenhouse gases abatement (CO 2 reduction through thermal- [182,183] or photo-catalytic processes [184]); photocatalytic [184] and electrocatalytic [185] hemi-reactions for fuel cells processes; and reactions for fine chemicals production [186]. Apart from these cases, there are only a few (yet remarkable) examples of MOFs employed as supports for catalysts employed as biomass valorization processer finalized to the production of higher added-value molecules.…”