Electrospun cobalt-ZIF micro-fibers for efficient water oxidation under unique pH conditions

Abstract

One dimensional (1D) materials are highly desirable in current platforms of materials chemistry owing to their unique physico-chemical properties. Herein, we report an effective way to synthesize 1D Co-ZIF microfibers using an electrospinning method, where a zeolitic imidazole framework (ZIF) with CoCl₂·6H₂O was prepared as the precursor for electrospinning. The synthesized microfibers were labeled after their post-spinning processing temperature as Co-ZIF-RT (without annealing), Co-ZIF-350 (annealed at 350 °C in air and a N₂ atmosphere) and Co-ZIF-550 (annealed at 550 °C in air and a N₂ atmosphere). All five microfibers were evaluated for the first time in electrocatalytic oxygen evolution reaction (OER) studies both in 0.5 M H₂SO₄ and 1 M KOH electrolytes. For the OER in 0.5 M H₂SO₄, Co-ZIF-550-N₂ delivered a superior activity and required an overpotential of 405 mV at a current density of 10 mA cm⁻² with a Tafel slope value of 281 mV dec⁻¹. For the OER in 1 M KOH, Co-ZIF-350-air gave better activity and required an overpotential of 370 mV and a lower Tafel slope value of 55 mV dec⁻¹. Fabricated materials showing promising activity for the OER both in acid and alkali implied that they can be adapted as a cost-efficient, cheaper alternative to commercially available IrO₂/C electrocatalysts. Moreover, in the future, the same synthetic protocol can be easily extended to the fabrication of other active metals incorporating ZIFs and the zeolite derived networks can also be utilized for other energy related applications.