Exposure of NiFe-LDH active sites by cation-exchange to promote photoelectrochemical water splitting performance

Abstract

NiFe -layered double hydroxides (LDH) are fast, responsive oxygen evolution co-catalysts (OECs) for photo-electrochemical (PEC) water splitting due to their extraordinary photo charge carrier transport properties, easy modulation of defect states, and low preparation cost. However, in NiFe-LDH, major catalytic active sites are situated at the edge sites, and the oxygen evolution active sites are impeded by the close-packed basal planes. Hence, activating these basal planes to participate in water oxidation is ideal for improving water splitting efficiency. In the present study, we synthesized NiFe-LDH by cation-exchange (NiFe-CE) and activated the basal planes for an efficient water oxidation reaction. After depositing NiFe-CE on BiVO4 nanostructures and measuring their maximum photocurrent density of 4.03 mA/cm(2) at 1.23 V vs. a reversible hydrogen electrode (RHE) under simulated solar light, the water oxidation efficiency was verified. Furthermore, their catalytic activity was compared with that of NiFe-LDH nanosheets synthesized through conventional techniques such as hydrothermal synthesis (NiFe-HT), solvothermal synthesis (NiFe-ST), and electrochemical deposition (NiFe-ED). The results demonstrated that NiFe-LDH derived through cation exchange exhibited higher catalytic activity than those that derived through other synthesis methods due to its abundance of catalytically active sites, high charge transport rate, and suitable water oxidation-reduction potentials. We hope that the present work provides a new way to activate catalytically active sites and facilitates the optimization of cost-effective, efficient, and durable oxygen evolution catalysts.