Fabricating bimetallic cobalt-iron MOF nano/microcrystalline particles: strong bifunctional electrocatalytic activity and overall water splitting

Abstract

Cobalt/iron terephthalic acid (CoFeTPA) metal organic frameworks with nano/microcrystalline structures were synthesized and investigated their bifunctional electrocatalytic OER, HER and overall water splitting in alkaline medium. Co-TPA produced microcrystalline particles whereas FeTPA produced nano/microrods. Bimetallic CoFeTPA exhibited broken microrods/particles with varying the ratio of Co and Fe. FeTPA showed relatively stronger OER activity (220 mV overpotential for 10 mA/cm2) compared to CoTPA and bimetallic CoFeTPA. In contrast, bimetallic CoFeTPA displayed better HER activity (202 mV overvoltage for 10 mA/cm2) compared to CoTPA and FeTPA. The strong bifunctional activity of CoFeTPA was utilized for overall water splitting. Bimetallic CoFeTPA catalyst required 1.68 V and cell voltage to achieve 10 mA/cm2 current density. The bimetallic MOF was further utilized for sea water splitting. The current-time studies indicated good stability of the catalyst for over 12 hr. After catalysis analysis indicated that bimetallic CoFeTPA MOF produced catalytic active cobalt oxyhydroxide and iron oxyhydroxide during the catalysis. Thus, the present work suggests the opportunity to fabricate cost effective bifunctional electrocatalyst by integrating multiple metal ions in the MOFs.