Trade-Off of Metal Sites in Fe-Ni Bimetal Metal-Organic Frameworks for Efficient CO 2 Photoreduction with Nearly 100% CO Selectivity.

This work disclosed the trade-off effect of two metal sites, which display distinct, key functionalities in naturally occurring and artificial catalysts for developing an advanced CO 2 reduction system. To exploit the metal-organic frameworks (MOFs) as advanced catalysts, we prepared a series of Prussian blue analogues (FeNi x PBAs) of tunable Ni/Fe molar ratio without changing the oxidation state of Fe and Ni for use as a photocatalyst in the CO 2 reduction reaction (CRR). The FeNi 0.66 PBA gives a superior CO yield rate (14.28 mmol·g -1 ·h -1 ) with nearly 100% CO selectivity, but the PBA would be basically CRR-inactive without either Ni or Fe. Experimental and calculation studies demonstrate that Fe and Ni display distinct functionalities. Specifically, Fe is an efficient mediator that boosts the electron transfer both from the photosensitizer to FeNi x PBA and from FeNi x PBA to CO 2 , and Ni serves as the active site for CO 2 adsorption and reduction. Intriguingly, when there is already sufficient Ni in the catalyst, further increase of the Ni content gives marginal gains in the CO 2 adsorption affinity that cannot offset the weakened electron transfer due to the Ni excess. The findings can help advance the design of bimetallic MOF catalysts that mimic naturally occurring bimetallic catalysts.