Breaking the inactivity of MXenes to drive Ampere-level selective oxygen evolution reaction in seawater

Abstract

The limited activity and stability of conventional anodes in seawater have posed a significant obstacle to sustainable green hydrogen production directly from seawater via electrolysis. To address these challenges, we engineered Ti 3 C 2 Tx-MXene by incorporating iron and boron into its matrix (tagged FBT) for selective oxygen evolution reaction (OER). Positioning B underneath the top layer induces charge disparity on the Fe-sites, which influences the subsequent growth of the ZIF-67 metal-organic framework (MOF) on the MXene surface through Fe-O-Co ionic bonds. DFT calculations reveal a favorable binding energy of −2.30 eV at the heterointerface for ZIF-67 adsorption to the surface of FBT via O-Co bond, a shortened bond length of 1.94 Å, confirming the formation of ionic bonds. These ionic bonds tune the active sites for an enhanced and selective OER over chlorine evolution reaction (CER), preventing active Fe species' leaching and ensuring stability at >1.56 A cm −2 in 6 M alkaline seawater over 370 hours. Further, FBT and ZIF-67/FBT require low overpotentials of 521.2 and 508 mV, respectively, to deliver 1 A cm −2 in 6 M alkaline seawater. Our findings demonstrate a robust strategy to significantly expand the potential of MXenes from simple conductive substrates to efficient OER catalysts for seawater splitting and beyond. We tune the composition of Ti 3 C 2 T x -Mxene by incorporating B and Fe into its matrix (FBT) to drive Ampere-level oxygen evolution reaction activity in seawater. With Fe acting as the active species, B underneath the top layer induces charge disparity that aids ionic bonding formation at the heterointerface when growing ZIF-67 on the FBT to produce a 2D/2D heterostructure. The ionic bonded heterostructure acts as a single unit, stable for over 370 hours at >1.56 A cm −2 current density and selective towards oxygen evolution reaction against chlorine evolution reaction in seawater. • Fe and B were successfully incorporated into the matrix of Ti 3 C 2 T x MXene (tagged FBT) while preserving the 2D morphology. • B underneath the top layer induces charge disparity on the Fe-sites, which aided the growth of ZIF-67 MOF on the FBT surface. • FBT and ZIF-67 are connected at the heterointerface through Fe-O-Co ionic bonds. • With Fe acting as the main active site, both FBT and ZIF-67/FBT exhibit ampere level OER activity in seawater. • The ionic bonding at the heterointerface ensures long-term stability and tune the active sites for selective OER over CER