Synthesis and characterization of NiO, MoO3, and NiMoO4 nanostructures through a green, facile method and their potential use as electrocatalysts for water splitting

NiO, MoO3, and NiMoO4 nanostructures were synthesized using a solution combustion method, employing agar as an organic fuel. TGA/DSC and BET analyses showed that the synthesis of NiO and NiMoO4 involved an intense exothermic combustion reaction that resulted in high surface area nanomaterials, with large pore volume and small pore size. XRD confirmed the phase composition and crystallite size of the synthesized materials. The particle size range was 20-40 nm for NiMoO4 and NiO, and 200-350 nm for MoO3. Band gap values of 3.44, 3.13, and 3.18 eV were determined for NiO, MoO3, and NiMoO4, respectively. Raman spectroscopy provided structural information about the synthesized materials, while FTIR results revealed that agar acts as both a metalion chelating agent and fuel. XPS confirmed the valence states of the produced materials and purported their purity, while the zeta potential measurements underpinned the stability of the samples in aqueous media. The synthesized materials were tested as potential electrocatalysts in water electrolysis for the oxygen (OER) and the hydrogen evolution reactions (HER) in an alkaline medium. The results demonstrated that NiMoO4 exhibits an excellent electrocatalytic activity in both OER and HER.