Bifunctional activity and theoretical study of transition metal molybdates for hydrogen and oxygen evolution reaction

Effective, sturdy and cheap electrocatalysts are extremely desirable for water electrolysis. In this work, transition metal molybdates (MMoO4, M = Fe, Co, Ni) with extraordinary oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) in basic electrolyte solution was reported. β-Fe2(MoO4)3 catalyst exhibits better electrocatalytic performance and robustness for both HER and OER compared to NiMoO4 and CoMoO4. Theoretical study (DFT calculation) disclose that the Fe atoms increase the energy states near the Fermi level in β-Fe2(MoO4)3 which makes it more conductive leading to superior OER and HER activity. Compared to CoMoO4 and NiMoO4, β-Fe2(MoO4)3 have well defined multiple Mo 4d orbitals at the conduction band. These are empty states in conduction band, ready to receive the electrons. Further, the computed overpotential values for NiMoO4, CoMoO4, and β-Fe2(MoO4)3 surfaces follow the trend, β-Fe2(MoO4)3 < NiMoO4 < CoMoO4, corroborating with the experimental results.