Atomic Bi substitution stabilized AgBi single-atom alloy with 4H/fcc heterophase interfaces for efficient CO2 reduction

Abstract

The pressing need to address global energy demand and climate change has positioned electrochemical CO₂ reduction into high-value chemicals as a crucial technology for carbon cycling and sustainable energy storage. However, precise control over the interfacial structure of active sites in single-atom alloy (SAA) remains a considerable challenge, significantly restricting their catalytic performance. In this study, we propose an atomic-level substitution strategy, integrating large atomic radius of Bi atoms into the Ag lattice to trigger and stabilize a 4H/fcc-Ag heterophase interfaces. Theoretical and experimental analyses reveal that the induced lattice strain stabilizes the metastable 4H phase and optimizes the geometric/electronic configuration of active sites, thereby enhancing the orbital overlap between Ag-3d and C-2p orbitals and lowering the energy barrier for *COOH formation. The optimal 4H/fcc Ag₄₉Bi₁ SAA catalyst, comprising approximately 3% 4H-Ag and 97% fcc-Ag, achieves CO Faraday efficiency (FE_CO) of 99.5%, single-pass conversion efficiency of 70%, CO yield of 45.6 mmol h⁻¹ cm⁻² and superior durability over 330 h under 200 mA cm⁻² in an alkaline flow cell. A membrane electrode assembly electrolyzer incorporating the catalyst reached a peak FE_CO of 98.6% at 150 mA cm⁻² and maintaining FE_CO >80% for 70 h under 100 mA cm⁻² without decay. When applied in a customized Zn-CO₂ battery, it delivered a peak power density of 0.86 mW cm⁻², along with 140 h cycling stability at 2 mA cm⁻². This work underscores the potential of atomic-level substitution for precise interface engineering, providing a novel strain-engineering strategy for designing high-performance SAA catalysts.