Surface/Interface Design And Mechanism Studies Of Two-Dimensional Materials Supported Bimetallic Cocatalysts In CO₂ Reduction

Photocatalytic reduction of CO₂ into renewable fuels provides opportunities for long-term energy storage and environmental protection.However,the lack of highly active and selective catalysts impedes the application of this reaction.Rational design of cocatalysts holds promise to address this grand challenge.In the development of photocatalysts,the surface and interface states of the photocatalytic materials are actually the key to restrict the photocatalytic performance.Therefore,it is very important to design the surface and interface of photocatalytic materials reasonably.Nowadays,two-dimensional materials supported bimetallic cocatalysts have attracted widespread attention from researchers due to their excellent photocatalytic performance.In this paper,we have prepared excellent photocatalysts by means of the orderly engineering of bimetallic cocatalysts,constructing heterojunctions and designing metal-to-metal interfaces,controlling surface strain and interface polarization,and studied their potential photocatalytic mechanism.The main research contents are as follows:1.With PdCu alloy nanoparticles as model cocatalysts,via the transformation from a random A1 alloy phase to an ordered B2 intermetallic phase,order engineering is performed on PdCu cocatalysts to realize enhanced photocatalytic activity and selectivity in reduction of CO₂ with H₂O to CH₄.Based on the experimental results of PdCu cocatalysts with different ordered degrees of atomic arrangement obtained through tuning the annealing temperatures and Pd/Cu molar ratios,two effects are proposed to contribute to this enhancement:（1）the strong electronic interaction between Pd and Cu atoms in the periodic structure increases the electron trapping ability of ordered PdCu cocatalysts;（2）the periodic structure increases the number of isolated Cu atoms in the ordered PdCu cocatalysts,which act as highly active catalytic sites in the reduction of CO₂ to CH₄.This work represents a step toward the design of high-performance photocatalysts through lattice engineering of the cocatalysts with atomic precision.2.With Janus Pd-Au heterojunctions as model cocatalysts,we demonstrate that the exposed Pd-Au interfaces act as highly reactive sites in conversion of CO₂ into CH₄.The experimental results indicate that the interfaces between Pd and Au play multiple roles in the enhancement of CO₂-to-CH₄ conversion:（1）Au atoms around the interface provide the sites for the reduction of CO₂ to*CO intermediates and then to CH₄;（2）*H intermediates are produced on adjacent Pd atoms on the other side of the interface,which further accelerate the rate-limiting process in conversion of*CO to CH₄;（3）charge re-distribution through the Pd-Au interface leads to substantial suppression of H₂ and CO evolution on electron-deficient Pd and electron-rich Au,respectively.This work provides fresh insights into the rational interface design of high-performance bimetallic cocatalysts for selective CO₂ photoreduction.3.With Pd@Au core-shell nanostructures with tunable Au thickness as model cocatalysts,we demonstrate the synergism of surface strain and interfacial polarization for enhanced photoreduction of CO₂ to CO.According to our experimental analysis and theoretical simulation,resulting from the mismatch in lattice parameters between the Pd core and the Au shell,compressive strain on the Au surface elevates the d-band center and improves the adsorption of key intermediate COOH*.Meanwhile,charge polarization,driven by the difference in electronegativity between Pd and Au,accelerates the interfacial charge transfer and increases the electron density on the Au surface.It is found that both effects are dependent on the thickness of the Au shell.As a result,a three-atom-thick Au shell dramatically boosts the overall efficiency in CO₂-to-CO conversion with an impressive activity of 166.3μmol g^-1_cat h^-1 and selectivity of 90.6%.This study can be viewed as a means of designing photocatalysts via the simultaneous control of surface catalytic reactivity and interfacial charge transfer in cocatalysts.