Engineering Proton-Deficient Micro-Environments on Co-cluster/atom Ensembles for Efficient Cyclooctasulfur Electrosynthesis From Sulfur Dioxide.

Electrochemical cyclooctasulfur synthesis (S8) from SO2 in an acidic media is a promising strategy for mitigating SO2 emissions and enabling sustainable sulfur recycling. However, achieving high S8 selectivity is challenging due to the competing hydrogen evolution reaction (HER). Here, Co-cluster/atom ensembles (CoC/SA-NC) were designed and attempted for the first time to achieve highly selective electrocatalytic conversion of SO2 to S8. Theoretical calculations have predicted that CoC/SA-NC possesses stronger SO2 adsorption and enhances proton diffusion into SO2 for SO2RR promotion. As expected, CoC/SA-NC experimentally facilitated SO2-to-S8 conversion through efficient hydrogenation and polymerisation, and created a local proton-deficient micro-environment to suppress HER. Consequently, the CoC/SA-NC ensembles attained a high Faradaic efficiency of 87% and a remarkable S8 yield of 2802.6 µmol mg-1 h-1. This performance considerably exceeds that of both commercial Pt@C (62%, 2007.2 µmol mg-1 h-1) and control NC (54%, 898.3 µmol mg-1 h-1) catalysts. Furthermore, the CoN4 atomic sites and Co clusters collaboratively reduce the affinity for S8 and produce a desulfurization interface that mitigates electrode passivation and improves catalyst stability, resulting in a potential retention of 80.5% after 7-cycles. This study provides valuable insight into tailoring the interfacial microenvironment using atom/cluster ensembles for efficient electrocatalytic S8 synthesis from SO2.