In-situ surface reconstruction of silver-based MOCHAs via chalcogen depletion for durable CO₂-to-CO electrocatalysis

Abstract

Metal–organic chalcogenolate assemblies (MOCHAs) have emerged as promising hybrid electrocatalysts for CO₂ reduction, but their long-term stability and structure–activity relationships remain poorly understood. Here, we compare selenium- and sulfur-based MOCHAs, [AgSePh]<inf>∞</inf> and [AgSPh]<inf>∞</inf>, immobilized on carbon paper via an optimized dip-coating strategy that yields homogeneous, high-utilization catalyst layers. Under batch conditions at −1.0 V vs RHE in 0.5 M KHCO₃, [AgSePh]<inf>∞</inf> reaches a CO faradaic efficiency of ∼96% with j<inf>CO</inf> ≈ 8 mA cm⁻², representing a clear improvement over previous reports on this material. In a continuous-flow configuration, [AgSePh]<inf>∞</inf> sustains CO production rates up to ∼275 mmol h⁻¹ g⁻¹ over 72 h, whereas [AgSPh]<inf>∞</inf> exhibits a gradual loss of activity, indicating superior durability of the selenolate-derived MOCHA. Pre- and post-electrolysis characterization (p-XRD, SEM/EDX, XPS, TXRF) reveals chalcogen depletion, metallic silver formation, and morphological roughening under cathodic bias, showing that both MOCHAs act as precatalysts that reconstruct into Ag-rich active phases. Complementary DFT calculations, including explicit-solvent ab initio molecular dynamics on pristine MOCHA surfaces, indicate somewhat stronger CO₂ interaction and a lower *COOH formation barrier for [AgSePh]<inf>∞</inf> than for [AgSPh]<inf>∞</inf>, providing qualitative insight into the higher CO₂RR activity and stability of the selenolate analogue. Together, these results identify chalcogen migration and depletion as a self-stabilization pathway for MOCHA-derived Ag electrocatalysts and establish [AgSePh]<inf>∞</inf> as a comparatively efficient and stable silver-based chalcogenolate catalyst for CO₂-to-CO conversion in H-cell and flow setups.