Structure and magnetic properties of an amine-templated one-dimensional cobalt-fluoro-sulfate containing Co4F4 cubane and hydrogen evolution reaction (HER) performance of its derived carbon-wrapped CoSe2 nanorods

Abstract

Amine-templated 1D cobalt fluoro sulfate of the composition [(CH₃)₂NH₂]₂[Co₄F₄(SO₄)₃(C₃N₂H₄)₄], consisting of Co₄F₄ cubane-type secondary building unit, has been synthesized under solvothermal condition. The magnetic properties of the Co₄F₄ cubane chain exhibited a low-temperature magnetic ordering below 17 K (T_c) attributed to intra-cluster ferromagnetic coupling and did not show spin-glass freezing. The selenylation of the Co₄F₄ cubane chain leads to the formation of sphere-like CoSe₂ in the hydrothermal route (CoSe₂@HT). At the same time, nanorods of CoSe₂ encapsulated with carbon matrix were obtained in a sealed tube method (CoSe₂@ST). Moreover, CoSe₂@ST exhibited a higher hydrogen evolution reaction (HER) activity than CoSe₂@HT in an acidic medium with 177 mV overpotential to achieve the benchmark current density of 10 mA cm⁻². The promising HER performance of derived CoSe₂@ST could be attributed to an increase in the geometrical and specific activity due to the encapsulation of N-doped carbon matrix over the CoSe₂ nanorods that facilitate faster charge transfer at the electrode–electrolyte interface and higher electrochemical conductivity than the derived CoSe₂@HT. This work demonstrates a low-temperature, solvent- and reducing agent-free new synthetic approach for synthesizing framework-derived materials.