Divergent Activity Shifts of Sn-Based Catalysts for Electrochemical CO2 Reduction: pH-Dependent Behavior of Single-Atom vs. Polyatomic Structures

Tin (Sn)-based catalysts have been widely studied for electrochemical CO2 reduction reaction (CO2RR) to produce formic acid, but the intricate influence of the structural sensitivity in single-atom Sn (e.g., Sn-N-C) and polyatomic Sn (e.g., SnOx and SnSx; x=1,2) on their pH-dependent performance remains enigmatic. Herein, we integrate large-scale data mining (with >2,300 CO2RR catalysts from available experimental literature during the past decade), ab initio computations, machine learning force field accelerated molecular dynamic simulations, and pH-field coupled microkinetic modelling to unravel their pH dependence. We reveal a fascinating contrast: the electric field response of the binding strength of *OCHO on Sn-N4-C and polyatomic Sn exhibits opposite behaviors due to their differing dipole moment changes upon *OCHO formation. Such response leads to an intriguing opposite pH-dependent volcano evolution for Sn-N4-C and polyatomic Sn. Subsequent experimental validations of turnover frequency and current density under both neutral and alkaline conditions well aligned with our theoretical predictions. Most importantly, our analysis suggests the necessity of distinct optimization strategies for *OCHO binding energy on different types of Sn-based catalysts.