MOF-Derived Co(Fe)OOH Slab and Co/MoN Nanosheet-Covered Hollow-Slab for Efficient Overall Water Splitting

The development of economical, efficient, and stable nonprecious metal electrocatalysts presents a crucial approach to achieving alkaline overall water splitting and generating renewable hydrogen. This work presents a simple method for the synthesis of transition metal oxyhydroxides and nitrides derived from the MOF template with different morphological structures for efficient overall water splitting. Co(Fe)OOH slab array is obtained by the electro-activation of Fe-doped Co-MOF precursor, which is usually regarded as the real active substance in the alkaline OER process. Doping the Co(Fe)OOH with Fe alters the local electronic structure of the Co sites, leading to a notable improvement in OER performance, which shows an overpotential of 209 mV at 10 mA cm^-2 and demonstrates excellent stability. On the other hand, Co/MoN nanosheet-covered hollow-slab heterostructure is prepared by the nitrogenization of Na₂MoO₄-etched Co-MOF template, which displays superior HER performance due to its abundant electrochemical active sites and rapid interfacial electron transfer, achieving an overpotential of 37 mV at 10 mA cm^-2 while sustaining good stability. Notably, utilizing Co(Fe)OOH as the anode and Co/MoN as the cathode in the alkaline electrolyzer results in a cell voltage of 1.49 V at 10 mA cm^-2, while demonstrating a remarkable long-term stability of 100 h. This work provides a facile way to construct an efficient alkaline electrolyzer for overall water splitting by controlling the structures of MOF derivatives.