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

Cobalt/iron terephthalic acid (CoFeTPA) based metal–organic frameworks (MOFs) with nano/microcrystalline structures were synthesized and their bifunctional electrocatalytic OER, HER and overall water splitting in alkaline medium were investigated. CoTPA produced microcrystalline particles whereas FeTPA produced nano/microrods. Bimetallic CoFeTPA exhibited broken microrods/particles with varying ratios of Co to Fe. FeTPA showed relatively stronger OER activity (220 mV overpotential for 10 mA cm⁻²) compared to CoTPA and bimetallic CoFeTPA. In contrast, bimetallic CoFeTPA11 displayed better HER activity (202 mV overvoltage for 10 mA cm⁻²) compared to CoTPA and FeTPA. The strong bifunctional activity of CoFeTPA was utilized for overall water splitting. The bimetallic CoFeTPA11 catalyst required 1.68 V cell voltage to achieve 10 mA cm⁻² current density. The bimetallic MOF was further utilized for seawater splitting. The current–time studies indicated good stability of the catalyst for over 12 h. XPS analysis performed after catalysis indicated that bimetallic CoFeTPA11 produced catalytically active cobalt oxyhydroxide and iron oxyhydroxide during the catalysis. Thus, the present work suggests the opportunity to fabricate cost-effective bifunctional electrocatalysts by integrating additional metal ions in the MOFs.