Electrochemical reduction of Hg2+ on Ti4O7@Ti: Integrating direct electron transfer with active hydrogen assistance

An N 2 -sintered Ti 4 O 7 @Ti cathode achieved >74% Hg 2+ removal in 5 h. • The Ti 4 O 7 @Ti cathode showed preliminary reuse performance in 10%H 2 SO 4 . • Ti 3+ /oxygen vacancies facilitate electron transfer and surface ·H formation. •Direct electron transfer dominated Hg 2+ removal, ·H played a secondary role. Highly toxic and bio-accumulative Hg 2+ can be electrochemically reduced to recoverable Hg 0 . However, preserving electrode integrity and corrosion resistance in strongly acidic media remains challenging. Magnéli-phase Ti 4 O 7 -coated electrodes were fabricated on Ti substrates. The optimized Ti 4 O 7 @Ti cathode, prepared by N 2 -protected sintering, preserved Ti 3+ species and oxygen vacancies, exhibiting a low charge-transfer resistance of 24.25 Ω and a high hydrogen evolution over-potential of −0.94 V vs. RHE. Under optimal conditions (3 V, 25 mm electrode spacing, 300 r·min −1 stirring), the cathode achieved >74.0% Hg 2+ removal within 5 h. Mechanistic analysis suggested that direct electron transfer was the primary Hg 2+ reduction pathway, with active hydrogen species as a secondary contributor. Detected Ti 3+ /oxygen vacancies may enhance interfacial electron transfer and surface active hydrogen generation. The electrode retains 68.0% removal after five cycles in 10%H 2 SO 4 . This work provides a stable Ti 4 O 7 -based cathode design for electrochemical Hg 2+ removal in strongly acidic media. Download: Download high-res image (294KB) Download: Download full-size image