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

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 (Co_C/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 Co_C/SA-NC possesses stronger SO₂ adsorption and enhances proton diffusion into SO₂ for SO₂RR promotion. As expected, Co_C/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 Co_C/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.