Facile Synthesis of Metal Oxides Sulphides and Phosphides for Enhanced Energy Applications (original) (raw)

Access to a reliable, sustainable, eco-friendly, and cost-effective energy supply is being challenged by the global increase in population and rapid technological advancement. Sophisticated systems, machinery, and various devices being innovated require a steady energy supply for their operations and applicability. To have this reliable energy, much research is being conducted through various approaches across the world. In this work, a facile approach in investigating and tuning the materials' properties was employed to improve the energy properties of metal oxides. Nanostructured NiFe oxide and CoFe oxide were synthesized using a facile coprecipitation method. It was revealed that nanostructured materials have favorable structures which promote their electrochemical efficiency. The structural and electrochemical properties of oxides were studied. To further investigate their properties, they were sulfurized and phosphorized using a hydrothermal and thermal process, respectively. The sulfides and phosphides showed impressive property improvement as compared to their respective oxides. NiFeoxide showed impressive oxygen evolution reaction and hydrogen evolution reactions with 298 mV and 54 mV overpotentials, respectively. After sulfurization, their results were further improved, except NiFe-oxide nanocubes (NiFe-NCs), whose HER overpotential was increased from 54 to 177 mV; while the rest of the samples showed v improvement of OER and HER overpotentials; from 298 for NiFe-NCs to 241 mV for NiFeS-NCs in OER, 258 for NiFe-oxide nanoparticles (NiFe-NPs) to 216 mV for NiFeS-NPs in OER; and 187 for NiFe-NPs to 152 mV for NiFeS-NPs in HER. Likewise, the materials' specific capacitance increased from 69 to 605 F/g for sulfurized NiFe-NCs and 186 to 515 F/g for sulfurized NiFe-NPs. The energy density of materials increased from 2 to 20 Wh/kg for NiFe-NCs and NiFeS-NCs, and from 6 to 17 Wh/kg for NiFe-NPs and NiFeS-NPs respectively, at 1 A/g. CoFe oxide samples showed good electrocatalytic and storage behavior. Their overpotentials decreased from 113 for CoFe-NCs to 52 mV for CoFeS-NCs and from 161 for CoFe-NPs to 122 mV for CoFeS-NPs. Their specific capacitance was also increased: specific capacitance of CoFe-NCs increased from 123 to 484 F/g for CoFeS-NCs and 161 of CoFe-NPs to 244 F/g for CoFeS-NPs. The energy density of CoFe-NCs increased from 4 to 17 Wh/kg after sulfurization, whereas for CoFe-NPs; the energy density increased from 5 to 8 Wh/kg, at 1 A/g. Upon phosphorization, the overpotentials values of 300, 330, 340, and 360 mV for phosphorized NiFe-nanoparticles (NiFeP-NPs), phosphorized CoFe-nanocubes (CoFeP-NCs), phosphorized NiFe-nanocubes (NiFeP-NCs) and phosphorized CoFe-nanoparticles (CoFeP-NPs) respectively, were observed, with some deviations from their unphosphorized counterparts which showed 256, 300, 298, and 300 mV overpotentials, respectively. The overpotentials for HER seemed to decrease when compared to their unphosphorized counterparts; 135, 121, 118, and 84 mV were determined for NiFeP-NPs, NiFeP-NCs, CoFeP-NPs, and CoFeP-NCs as compared to their unphosphorized samples vi overpotentials of 187, 54, 161, and 113 mV respectively. Specific capacitances of phosphorized samples were significantly improved; for CoFe-NCs, it increased from 123 to 248 F/g, 161 to 464 F/g for CoFe-NPs, 69 to 424 F/g for NiFe-NCs, and 186 to 214 F/g for NiFe-NPs. At the same time, the energy densities increased after phosphorization as shown in the following order; from 4 Wh/kg for CoFe-NCs to 9 Wh/kg for CoFeP-NCs, from 5 Wh/kg for CoFe-NCs to 16 Wh/kg for CoFeP-NPs, from 2 Wh/kg for NiFe-NCs to 15 Wh/kg for NiFeP-NCs, and from 6 Wh/kg for NiFe-NPs to 7 Wh/kg for NiFeP-NPs. The results of this study suggest that facile sulfurization and phosphorization of nanostructured NiFe oxides and CoFe oxides could significantly improve their electrocatalytic and capacitive behavior. vii