Understanding the Affinity Effect of C/O-Correlative Intermediates for the Selective Electrosynthesis of HCOOH

The linear scaling relationship among correlative adsorbents brings great challenges in adjusting the selectivity for competing products. In this work, we discovered an exception for regulating product selectivity while obeying a linear scaling relationship. Typically, metallic Sn nanoparticles with compressive strain (denoted as compressed Sn NPs) were employed as model catalysts for the case study toward CO₂ electroreduction. When the applied current density (j) was set from −400 to −1200 mA cm^–2, all of the selectivity for HCOO^– among carbon products over compressed Sn NPs was higher than that over pristine Sn NPs in the flow cell. Notably, compressed Sn NPs achieved a selectivity for HCOO^– of 99.9% among carbon products at an applied j of −1200 mA cm^–2. The performance of compressed Sn NPs outperformed all of those of the previously reported metallic Sn-based catalysts in recent years. In situ spectroscopy measurements and density functional theory calculations revealed that Sn (200) with high O-affinity exhibited strong adsorption for *OCHO, making *OCHO protonation the potential-limiting step (PLS) for the formation of HCOOH. Nevertheless, the PLS for the formation of CO was CO₂ protonation due to the weak adsorption of *COOH. The introduction of compressive strain in Sn (200) diminished the barrier for the PLS of HCOOH production whereas raised that of CO production by reducing the adsorption of both *OCHO and *COOH, thereby promoting the selectivity for HCOOH.