Unveiling the impact of oxygen vacancies in engineered bimetallic oxides for enhanced oxygen evolution reaction: insights from experimental and theoretical approaches

Abstract

In this study, we presented hollow bimetallic mixed oxides of molybdenum and nickel, prepared through a facile polymer-assisted solution process. Our focus was on addressing the influence of polymer concentration on the formation of hollow nanoparticles (HNPs) of the bimetallic mixed oxides, a critical aspect explored through XRD, Raman, and TEM analyses. Raman study indicated that as the PAA concentration increases, the oxygen vacancies become more dominant with a decrease in the O/Mo ratio. The formation process of the hollow structure in the MoO₃/NiMoO₄ nanostructure was confirmed using FESEM and TEM. The influence of oxygen vacancies over the surface of the mixed oxides and their concentration was examined by XPS analysis. The resulting MoO₃/NiMoO₄ HNPs serve as catalysts for the oxygen evolution reaction (OER), and their performance was systematically investigated using ECSA, EIS, CV, and LSV analyses. The superior electrochemical performance of the optimized mixed oxide composite is attributed to the increased number of oxygen vacancies, electrical conductivity, and a reduced Tafel slope. Notably, the best composite exhibits a 3-fold increase in electrochemical surface area and a lower overpotential. Specifically, the reduction in the Tafel slope from 142.2 to 97.5 mV dec⁻¹ and the overpotential from 402 to 330 mV for HNPs prepared with PAA 0.10 g/10 mL and PAA 0.15 g/10 mL, respectively, underscores the efficacy of the developed catalyst. DFT calculations of the OER were found to be uphill in energy which makes the *O to *OOH step the PDS for defective metal oxide with a ΔG of 3.00 eV. This research contributes valuable insights that open new avenues for the application of molybdenum oxides and their derivatives in water-splitting processes. The findings not only address the challenges in OER kinetics but also hold promise for advancing the field of green hydrogen production through enhanced electrocatalytic materials.