1. Introduction
2. Materials and Methods
2.1 Synthesis
2.2 Instrumentation
2.3 Modification of the electrode
3. Results and Discussion
3.1 Structural Properties
3.1.1 Crystal Structure Analysis
3.1.2 Thermodynamic Analysis
3.1.3 Microstructure Analysis by SEM
3.2 Thermal Properties
3.2.1 Thermogravimetric Analysis
3.2.2 Differential Scanning Calorimetry
4. Electrochemical Studies
4.1 Electrochemical response of (Be,Mg,Ca,Sr,Zn,Ni)3O4 HEOx on bare glassy GC electrode
4.2 Hydrazine hydrate oxidation
4.3 Water Oxidation
4.4. Comparison of Catalytic Potential in Water Oxidation and Hydrazine Hydrate Oxidation
5. Conclusions
Structural properties reconnoitered by XRD and SEM analyses gave insight into the crystal structure and microstructure of HEOx understudy respectively. XRD confirmed that the (Be,Mg,Ca,Sr,Zn,Ni)3O4 HEOx possesses a single-phase with Fd-3m spinel structure and the crystallite size in the nanometer regime. SEM results show that the HEOx exhibits irregular morphology and the agglomerations of nanoparticles. It is attributed to the fact that the air quenching locks the crystal structure and particle size of compounds at high temperatures. Hence, (Be,Mg, Ca,Sr,Zn,Ni)3O4 HEOx is, in fact, nanocrystalline.
Thermal properties of sintered and air quenched (Be,Mg,Ca,Sr,Zn,Ni)3O4 HEOx explored by TGA and DSC revealed that it possesses excellent thermal stability showing no major weight loss or weight gain in TGA curve up to the studied temperature of 1200°C. Moreover, the DSC curve shows the creation of oxygen vacancies around 470°C making it a potential candidate to be used as a catalyst especially in water oxidation, and hydrazine hydrate oxidation, etc.
Electrochemical applications of (Be,Mg,Ca, Sr,Zn,Ni)3O4 HEOx studied through CV gave an insight into its potential to catalyze both water and hydrazine hydrate oxidation. Among kinetic parameters, the values of Do (6.14 exp−5 cm2 s−1) and ko (1.26 exp−2 cm s−1) are higher for water oxidation as compared to hydrazine hydrate oxidation (Do = 6.72 exp−5 cm2 s−1, ko = 7.93 exp−3 cm s−1). Moreover, the comparative thermodynamic values for water oxidation (ΔG* = 13.67 kJ mol−1, ΔH* = 6.84 kJ mol−1) and hydrazine hydrate oxidation (ΔG* = 22.90 kJ mol−1, ΔH* = 11.49 kJ mol−1) also reflect that electrocatalysis of water oxidation is more facile at room temperature. Hence, both kinetic and thermodynamic values depict that the water oxidation is more facile on (Be,Mg,Ca,Sr,Zn,Ni)3O4 HEOx surface as compared to hydrazine hydrate oxidation.