Intercalation Chemistry Awakens Transition Metal Hydroxide for Boosted and Sustained Electrocatalytic Sulfion...

Electrocatalytic sulfion oxidation reaction (SOR) is a sustainable approach to treat sulfion-rich sewage for S recovery. Transition metal hydroxide (TMOH), utilized in various electrocatalysis, yet is clumsy in SOR due to overstrong adsorption toward S-containing intermediates from unsuitable electronic structure. Herein we report, for the first time, that the SOR performance of TMOH can be awakened by intercalation chemistry. Take Co(OH)₂ as a proof-of-concept demonstration, MoO₄ ^2- intercalated Co(OH)₂ 2D nanosheet array is engineered, and presents remarkably enhanced SOR behavior with an ultralow potential of 0.29 V versus RHE to attain 100 mA cm^-2, a record Tafel slope of 27.7 mV dec^-1, and stable operation for 192 h without appreciable deterioration. The experimental and theoretical studies unveil that MoO₄ ^2--intercalated nanoarray is advantageous for active site exposure, and boosting mass transport with enhanced sulfion enrichment and superhydrophilicity. Impressively, MoO₄ ^2- intercalation can manipulate electronic structure of Co(OH)₂ with downshift of d-band center, thereby weakening binding strength with HS^- and S₈, and decreasing the |ΔG_s*|, eventually enhancing both activity and stability. Notably, such intercalation wake-up strategy for the SOR is general and can be extended to other oxometallate intercalated TMOH systems. This contribution provides a new paradigm to evoke TMOH for SOR electrocatalysis via elegant intercalation tactic.