Hydrazine oxidation-assisted electrocatalytic water splitting with Prussian blue analog-derived V-doped CoFe-layered double hydroxide nanosheets†

Efficient and sustainable hydrogen production through electrocatalytic water splitting remains a critical challenge, hindered primarily by the sluggish oxygen evolution reaction (OER). In this regard, leveraging the hydrazine oxidation reaction (HzOR) as an anodic alternative significantly lowers the overall cell voltage, promoting energy-efficient hydrogen evolution. In this study, we report Prussian blue analog (PBA)-derived vanadium-doped cobalt-iron layered double hydroxide (V-CoFe-LDH) nanosheets as an efficient electrocatalyst for the HzOR in the alkaline medium. The PBA-derived V-CoFe-LDH offered a high surface area, large porosity, and coordination unsaturation, and produced 2D nanosheets. The introduction of mixed-valence V⁴⁺/V⁵⁺-species modulated the electronic structure and enhanced the active site density, offering facile access to the higher oxidation states of Co and Fe-ions to improve the catalytic performance. The V-CoFe-LDH exhibited superior HzOR activity, achieving a significant reduction in the potential requirement (0.70 V in 3-electrode and 0.42 V in 2-electrode systems) compared to the anodic OER. Moreover, the structural modification in PBA-derived V-CoFe-LDH led to an improved HzOR compared to the hydrothermally prepared V-CoFe-LDH-HT. The operando Raman studies elucidated the formation of the *NH₂ intermediate on the V-CoFe-LDH surface, and further confirmed the breaking of the N–N bond during the HzOR.