Experimental and DFT study of the MoO2@Fe2O3 catalyst for overall water splitting in acidic and alkaline electrolytes

Abstract

Energy is an essential component of human life. Among the various forms of energy generation, water splitting using electricity is a non-polluting green method that produces both hydrogen and oxygen. This research presents a unique methodology involving the hydrothermal synthesis of MoO₂@Fe₂O₃ on a stainless steel (SS) substrate, aimed at facilitating overall water splitting in both acidic and alkaline environments. Various analytical techniques, including XRD, SEM, FE-SEM, FTIR, and UV-vis DRS, were utilized to characterize the structural, morphological, and optical properties of the synthesized materials. We also employed density functional theory (DFT) to calculate the work of adhesion and bulk modulus for MoO₂, Fe₂O₃ and MoO₂@Fe₂O₃. Comparative electrochemical analysis revealed that the MoO₂@Fe₂O₃ thin films exhibited reduced overpotential for overall water splitting in KOH compared to that in H₂SO₄ electrolytes. Specifically, in KOH and H₂SO₄ electrolytes, the films demonstrated cell voltages of 1.75 V vs. RHE and 1.80 V vs. RHE, respectively. Moreover, Tafel slopes were observed to be lower in acid electrolytes than in alkaline electrolytes. Regarding stability, the interfaced electrode displayed promising performance, with 14 hours and 8 hours of stability for the OER and HER, respectively, in the KOH electrolyte, and 12 hours and 6 hours of stability for the HER and OER, respectively, in the H₂SO₄ electrolyte. We determined the interfacial work of adhesion and bulk modulus using DFT, which suggested a stable interfacial structure for MoO₂@Fe₂O₃. This confirms the drifting of Mo atoms towards Fe atoms, resulting in the production of oxygen vacancies, which create a mid-band gap, suggesting good metallic range conductivity, which is also evident from the decreased band gap value for MoO₂@Fe₂O₃. DFT studies together with experimental results propose a new strategy offering great possibilities to tune the selectivity of photo-catalytically active metal oxide materials.