In situ generated layered NiFe-LDH/MOF heterostructure nanosheet arrays with abundant defects for efficient alkaline and seawater oxidation

As the main limiting step of overall water splitting, oxygen evolution reaction (OER) is urgent to be enhanced by developing efficient catalysts to promote the process of electrolytic water. Based on theoretical analysis, the Ni-metal-organic framework (Ni-MOF) and NiFe-layered double hydroxide (NiFe-LDH) (NiFe-LDH/MOF) heterostructure can optimize the energy barrier of the OER process and decrease the adsorption energy of oxygen-containing intermediates, effectively accelerating the OER kinetics. Accordingly, layered NiFe-LDH/MOF heterostructures are in situ constructed through a facile two-step reaction process, with substantial oxygen defects and lattice defects that further improve the catalytic performance. As a result, only 208 and 275 mV OER overpotentials are needed for NiFe-LDH/MOF to drive the current densities of 20 and 100 mA·cm⁻² in 1 M KOH solutions, and even maintain catalytic stability of 100 h at 20 mA·cm⁻². When applied to seawater oxidation, only 235 and 307 mV OER overpotentials are required to achieve the current densities of 20 and 100 mA·cm⁻², respectively, with almost no attenuation for 100 h stability test at 20 mA·cm⁻², all better than commercial RuO₂. This work provides the theoretical and experimental basis and a new idea for efficiently driving fresh water and seawater cracking by heterostructure and defect coupling design toward catalysts.