A surface reconstructing phenomenon is discovered on a defect-rich ultrathin Pd nanosheet catalyst for aqueous CO 2 electroreduction. The pristine nanosheets with dominant (111) facet sites are transformed into crumpled sheet-like structures prevalent in electrocatalytically active (100) sites. The reconstruction increases the density of active sites and reduces the CO binding strength on Pd surfaces, remarkably promoting the CO 2 reduction to CO. A high CO Faradaic efficiency of 93 % is achieved with a site-specific activity of 6.6 mA cm À2 at a moderate overpotential of 590 mV on the reconstructed 50 nm Pd nanosheets. Experimental and theoretical studies suggest the CO intermediate as a key factor driving the structural transformation during CO 2 reduction. This study highlights the dynamic nature of defective metal nanosheets under reaction conditions and suggests new opportunities in surface engineering of 2D metal nanostructures to tune their electrocatalytic performance.

The cover image is based on the Overview Two dimensional ferroelectrics: Candidate for controllable physical and chemical applications by Jing Shang, Xiao Tang, and Liangzhi Kou., https://doi.org/10.1002/wcms.1496.

The NO reduction reaction (NORR) toward NH3 is simultaneously emerging for both detrimental NO elimination and valuable NH3 synthesis. An efficient NORR generally requires a high degree of activation of the NO gas molecule from the catalyst, which calls for a powerful chemisorption. In this work, by means of first-principles calculations, we discovered that the NO gas molecule over the Janus WSSe monolayer might undergo a physical-to-chemical adsorption transition when Se vacancy is introduced. If the Se vacancy is able to work as the optimum adsorption site, then the interface’s transferred electron amounts are considerably increased, resulting in a clear electronic orbital hybridization between the adsorbate and substrate, promising excellent activity and selectivity for NORR. Additionally, the NN bond coupling and *N diffusion of NO molecules can be effectively suppressed by the confined space of Se vacancy defects, which enables the active site to have the superior NORR selectivity in the NH3 synthesis. Moreover, the photocatalytic NO-to-NH3 reaction is able to occur spontaneously under the potentials solely supplied by the photo-generated electrons. Our findings uncover a promising approach to derive high-efficiency photocatalysts for NO-to-NH3 conversion.