Capture and recycling of toxic selenite anions by cobalt-based metal-organic-frameworks for electrocatalytic overall water splitting

A nanosheet-like cobalt-based metal-organic-framework (Co-MOF) is employed to uptake SeO32− anions, and the remove capacity of Co-MOF reaches a record of 280.0 mg g−1. After uptake SeO32− by Co-MOF, the recycling defect-rich CoSeO4 (R-CoSeO4) is used as an electrocatalyst for oxygen evolution reaction (OER), which displays an overpotential of 265 mV at 10 mA cm−2 in 1 M KOH. Furthermore, cobalt-cobalt selenide heterojunction nanoparticle (Co-Co0.85Se), a high-performance hydrogen evolution reaction (HER) electrocatalyst (overpotential of 97 mV at 10 mA cm−2 in 1 M KOH) is obtained by one-step calcining of R-CoSeO4. Series experiments and density functional theory calculations confirm the anion vacancy in R-CoSeO4 and heterojunction in Co-Co0.85Se can improve the OER and HER activity, respectively. Finally, two binder-free electrodes (R-CoSeO4/CC and Co-Co0.85Se/CC) are employed as anode and cathode, respectively, to construct a water electrolysis cell, which only needs 1.47 V to achieve 10 mA cm−2 in 1 M KOH.