Electronic Feature Modification of Ni and Co Free Metal–Organic Framework Nanoparticles by Vanadium Introduction for Water Oxidation

Abstract

Electrocatalytic water splitting has emerged as an innovative technique for producing green hydrogen fuel. In this regard, a series of electrocatalysts based on Ni and Co have been investigated for improved oxygen evolution activity. However, the reliance on Ni and Co constraints the development of cost-effective electrocatalysts and presents challenges for advancing innovation in this field. In this work, we developed Ni- and Co-free VFe-MOF nanoparticles exhibiting remarkable electrocatalytic performance for electrocatalytic water oxidation. Spectroscopic analysis revealed that the V-introduction induced easier access to high valent Fe³⁺ due to its electronic withdrawing nature altering the electronic features of the Fe-MOF. Easier access of Fe³⁺ led to the accessible O–O bond formation, boosting the catalytic reactivity. Consequently, VFe-MOF nanoparticles achieved superior oxygen evolution reaction (OER) activity, surpassing the performance of CoFe- and NiFe-MOF counterparts. It demonstrated a notably low overpotential of 220 mV at a current density of 10 mA cm^–2, outperforming Fe-MOF, CoFe-MOF, and NiFe-MOF. The incorporation of high-valent vanadium significantly enhanced the electronic properties of the Fe-MOF, accelerating OER kinetics and increasing the number of reactive sites and surface area, which collectively boosted catalytic performance. Additionally, the VFe-MOF achieved a high faradaic efficiency (FE) of 97.6% for OER, reflecting its intrinsic catalytic efficacy. Postcatalytic analysis indicated that VFe-MOF undergoes electrochemical reconstruction into an active Fe(O)OH phase, which serves as the true active species for OER.