FeCoSe 2 Nanoparticles Embedded in g-C 3 N 4 : A Highly Active and Stable bifunctional electrocatalyst for overall water splitting.

To investigate cost affordable and robust HER and OER catalysts with significant low overpotentials, we have successfully embedded FeCoSe ₂ spheres on smooth surfaces of graphitic carbon nitride that demonstrated high stability and electrocatalytic activity for H ₂ production. We systematically analyzed the composition and morphology of Fe _x Co _1-x Se ₂ /g-C ₃ N ₄ and attributed the remarkable electrochemical performance of the catalyst to its unique structure. Fe _0.2 Co _0.8 Se ₂ /g-C ₃ N ₄ showed a superior HER activity, with quite low overpotential value (83 mV at -20 mA cm ^-2 in 0.5 M H ₂ SO ₄ ) and a current density of -3.24, -7.84, -14.80, -30.12 mA cm ^-2 at 0 V (vs RHE) in Dulbecco's Phosphate-Buffered Saline (DPBS), artificial sea water (ASW), 0.5 M H ₂ SO ₄ and 1 M KOH, respectively. To the best of our knowledge, these are the highest reported current densities at this low potential value, showing intrinsic catalytic activity of the synthesized material. Also, the catalyst was found to deliver a high and stable current density of -1000 mA cm ^-2 at an overpotential of just 317 mV. Moreover, the synthesized catalyst delivered a constant current density of -30 mA cm ^-2 for 24 h without any noticeable change in potential at -0.2 V. These attributes confer our synthesized catalyst to be used for renewable fuel production and applications.