Manickam Minakshi Sundaram

This review investigates the potential of molybdate nanocomposites with the general formula ABO4 (A = Mg, Ca, Sr, or Ba; and B = Mo) as advanced electrode materials for aqueous energy storage systems. Electrochemical energy storage technologies, such as supercapacitors and batteries, offer distinct advantages over mechanical and thermal systems, including higher energy efficiency, faster response times, modular scalability, and integration with renewable energy sources.

Among the various electrochemical energy storage technologies, supercapacitors are distinguished by their high-power density, rapid charge–discharge rates, and long cycle life, positioning them as strong candidates for next-generation applications. Binary transition metal oxides (BTMOs) such as cobaltates, ferrates, manganates, vanadates, and molybdates have been extensively studied due to their superior electrochemical performance, owing to their multiple redox states, structural stability, and high electrical conductivity, largely attributed to the synergistic interactions between transition metal ions. In comparison, binary metal oxides (BMOs) with the general formula MMoO₄ (M = Mg, Ca, Sr, or Ba) represent a distinct class of oxides with distinguishing crystallographic features. Their crystal structures are influenced by the ionic radius of the divalent cation: wolframite-type structures form when A = Mg (<0.99 Å), while scheelite-type structures are observed for Ca, Sr, and Ba (>0.99 Å). Specifically, MgMoO₄ typically adopts the wolframite structure, characterized by octahedral coordination of Mo, whereas CaMoO₄, SrMoO₄, and BaMoO₄ generally crystallize in the scheelite structure, where Mo is tetrahedrally coordinated. Despite their structural versatility and inherent stability, BMOs with ABO₄-type composition remain underexplored compared to BTMOs. However, their tunable crystal chemistry and the combined properties of alkaline-earth and transition-metal elements make them promising materials for advanced supercapacitor electrode materials.

This review summarizes recent progress in doping and hybridization strategies aimed at enhancing the electrochemical performance of BaMoO4 and related molybdate-based materials. Doping can effectively alter charge carrier concentrations and tailor electronic properties, thereby improving energy storage capabilities. Although doping can significantly enhance charge transport and electrochemical activity, the synthesis of well-defined molybdate nanostructures remains a major challenge, limiting their scalability and practical deployment. A promising approach involves the hybridization of BaMoO₄ with ZnO, a semiconductor renowned for its excellent electrical conductivity and mechanical robustness. Combustion synthesis of BaMoO₄/ZnO nanocomposites has yielded materials with improved energy and power densities, demonstrating synergistic effects between the two components. These advancements underscore the growing potential of BaMoO₄/ZnO-based systems in the development of sustainable and high-performance energy storage technologies.

As part of 2025 International Open Access Week activities, Murdoch University Library hosted a panel discussion on the OA week theme of "Who owns our knowledge?"

Panellists shared their expertise and insights in areas prompted by the theme, including open access publishing, integrating Indigenous knowledges, social construction of knowledge, and creative commons licensing.

The resulting discussion was a fascinating exploration of the theme, highlighting the value of sharing perspectives across disciplines and collaboration with other University areas. The webinar recording allows further reflection on the creation and sharing of knowledge.

Copper is a promising alternative to conventional plasmonic materials, though its practical use is hindered by a strong tendency to oxidize. Through systematic analysis of its vibrational, optical, morphological, structural, and surface potential properties, we confirmed the stability of copper (Cu) particles and highlighted the role of functional groups in modulating their oxidation susceptibility. Oxidation kinetics at 150 °C, in the presence of antioxidants and capping agents, as well as long-term colloidal stability, appear closely tied to the degradation of these stabilizers, which correlates with particle aggregation. Notably, precursor chemistry significantly affects oxidation behavior. Varying concentrations of polyvinylpyrrolidone (PVP) demonstrate a positive correlation with particle size control and thermal stability, indicating that PVP enhances oxidation resistance under the tested conditions. Our findings underscore most importantly the metallic phase’s stability after exposure to air at a temperature of 150 °C, drawing attention to a possible precursor and capping agent combination that can result in oxidation-stable Cu particles, positioning them as cost-effective candidates for replacing more expensive plasmonic metals across diverse applications.

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Biomass-derived porous carbon electrodes have attracted significant attention for high-performance supercapacitor applications due to their sustainability, cost-effectiveness, and tunable porosity. To accelerate the design and evaluation of these materials, it is essential to develop accurate and efficient strategies for optimizing their physicochemical and electrochemical properties. Herein, a machine learning (ML) approach is employed to analyze experimental data from previously reported sources, enabling the prediction of specific capacitance (F g−1) based on various material characteristics and processing conditions. The trained ML model evaluates the influence of factors such as biomass type, electrolyte, activating agent, and key synthesis parameters, including activation and carbonization temperatures and durations, on supercapacitor performance. Despite growing interest, comprehensive studies that correlate these variables with performance metrics remain limited. This work addresses this gap by using ML algorithms to uncover the interrelationships between biomass-derived carbon properties, synthesis conditions, and specific capacitance. Herein, it is demonstrated that an optimal combination of a carbonized honeydew peel to H3PO4 ratio of 1:4 and an activation temperature of 500 °C yields a highly porous carbon material. When used in a symmetric device with 1 M H2SO4 electrolyte, this material, rich in oxygen and phosphorus species, achieves a high specific capacitance of 611 F g−1 at a current density of 1.3 A g−1. Correlation analysis reveals a strong synergy between surface area and pore volume (correlation coefficient = 0.8473), and the ML-predicted capacitance closely aligns with experimental results. This ML-assisted framework offers valuable insights into the critical physicochemical and electrochemical parameters that govern supercapacitor performance, providing a powerful tool for the rational design of next-generation energy storage materials.

Nano hexagon NiCeO2 is synthesized via a simple one-pot hydrothermal method and evaluated as a highly efficient electrocatalyst for the oxygen reduction reaction (ORR) in an Al-air battery (AAB). Structural analysis using X-ray diffraction reveals peak shifts and lattice contraction, confirming the successful incorporation of Ni into the CeO2 host matrix. Raman spectroscopy identified a characteristic peak associated with oxygen vacancies, indicating defect formation. Thermogravimetric analysis showed a 4.97% weight gain, likely due to the filling of oxygen vacancies at elevated temperatures. Transmission electron microscope revealed a nano hexagon morphology with an average particle size of 20 nm. X-ray Photoelectron Spectroscopy analysis confirmed the presence of both cerium and nickel elements. Electronic structure calculations, performed using density functional theory via Quantum ESPRESSO, indicated that Ni doping introduces new 3d states into the CeO2 band structure, resulting in bandgap narrowing and a lowered Fermi level. Electrochemical testing demonstrated that NiCeO2 exhibits superior ORR performance compared to commercial Pt/C catalysts. Kinetic analysis suggested a near four-electron transfer pathway. Durability is assessed using chronoamperometry, showing that NiCeO2 retained 90% of its initial current after 20 h of operation, outperforming Pt/C. Furthermore, an AAB is constructed using NiCeO2 as the cathode, which achieved an open circuit voltage of 1.65 V with a discharge capacity of 1070 mAh·g−1, delivering a notable power density of 77.64 mW·cm−2. The enhanced ORR activity is attributed to the synergistic interaction between CeO2 and Ni, which significantly improves the overall performance of the AAB These findings suggest that NiCeO2 is a promising cathode material for high-performance AABs.

Electrolysis of MnSO4 in H2SO4 with cationic surfactants (tetradecyltrimethylammonium bromide; TTAB and cetyltrimethylammonium bromide; CTAB) led to the formation of γ-MnO2 with surfactant intercalation in an amorphous matrix. Unlike conventional self-standing EMD electrodes, which limit scalability, this study presents bulk electrodeposition of EMD powder on a lead (Pb) anode. Surface morphology is significantly altered by surfactant presence, though X-ray diffraction and density functional theory analyzes confirms consistent γ-MnO2 crystallography across samples. Galvanostatic charge–discharge at 0.6 A g−1 reveals that TTAB-assisted EMD achieved a specific capacitance of 478.6 F g−1, double that of pristine EMD (232 F g−1), due to improved ion transport and surface area. In contrast, CTAB-assisted EMD shows reduced capacitance (124.6 F g−1), attributed to early micelle formation and immobilization within the MnO2 lattice, which promoted SO42− insertion over surfactant deintercalation. Surfactant critical micelle concentrations and surface activity are key to electrochemical behavior in 1 M Na2SO4. An asymmetric device using TTAB-EMD as the cathode and activated carbon as the anode delivered 106 F g−1 and 40 Wh kg−1, demonstrating practical viability. Band structure calculations support the experimental findings, indicating favorable electronic properties for charge storage.

The sodium cobalt pyrophosphate (Na2CoP2O7) forms a diphosphate (PO4–PO4) compound, which exhibits allotropic evolution from the rose phase of a triclinic structure to the blue phase of a tetragonal crystal structure. Enhanced electrochemical performance of the two allotropic forms arises from changes in the orientation of the surface oxide layer and morphology. The triclinic rose phase structure of Co6−4 and PO4−3, features a staggered conformation with tunnels. Sodium ions are housed in these tunnels for ion exchange. Ionic intercalation/deintercalation occurs between the oxide layers, facilitating reversible charge storage processes. In this work, we adopted this mechanism for energy storage hybrid devices with an asymmetric configuration. In the proposed hybrid device, the battery charge storage mechanism from the Na2CoP2O7 cathode is coupled with a capacitive-type activated carbon anode to enhance device performance. The hybrid electrochemical cell demonstrates an excellent energy density of 50.2 Wh kg−1 at a maximum power density of 662.8 W kg−1, with long cycle retention of up to 10,000 cycles for the rose allotropic form of sodium cobalt pyrophosphate. The key parameters obtained from the hybrid device have been used for simulation to understand the interplay between kinetics and electrochemistry in the electrodes. The electrode-electrolyte interfacial layers show a wide distribution of ions in the hybrid device.

Nano‐octahedron cobalt oxide decorated graphene nanocomposite is reported in this work for selective and simultaneous determination of dopamine (DA) and uric acid (UA). The composite is synthesized using a hydrothermal method and characterized to identify the crystal structure and its shapes. The Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) images indicate the silhouette image of the nanocube decorated over graphene oxide. The Gr‐Co₃O₄/glassy carbon electrode (GCE) is utilized for the electrochemical detection of dopamine (DA). Cyclic voltammetry (CV) studies revealed a significant breakthrough such as Gr‐Co₃O₄/GCE exhibited higher electrocatalytic activity for DA oxidation than the bare GCE. Differential pulse voltammetry (DPV) measurements demonstrated a detection limit of 0.09 µM for DA, with a linear response range from 1 to 500 µM. For uric acid (UA), the detection limit and linear range are estimated as 0.2 and 100 to 8000 µM, respectively. The sensor selectively detects DA in the presence of UA is confirmed, with a peak separation of 250 mV between DA and UA. The reliability of the sensor is validated through using human serum specimens, paving the way for exciting potential applications in biomedical research and clinical diagnostics.

Numerical computations through the finite element method (FEM) are used to determine the impact of doping on carrier concentration and recombination between charges in time for organic semiconductor diodes having low mobility. The Hall effect is used to determine the effects of doping on the performance and reliability of organic semiconductor devices by accurately modeling these processes. In this work, the number density of charge carriers and Hall voltages are computed for n-type doped semiconductors with two different recombination processes, such as non-Langevin and Langevin-type. The findings reveal that in the Langevin system with 𝛽′=1, the number density of charge carriers is almost five and four times lower compared with the non-Langevin system with 𝛽′=0.01 for increasing dopant concentrations of 𝑁𝑝𝑑 = 1 and 3, respectively. The Langevin system also had lower Hall voltages than the steady-state and non-Langevin systems for different magnetic fields with dopants, and the non-Langevin system had nearly identical Hall voltages as the steady-state case. The outcome of the current work provides insights into charge transportation mechanisms in low-mobility doped organic semiconductors with Hall effect measurements to improve device efficiency.

In this work we developed a hydrothermal method for synthesizing amorphous Ni−Co hydroxide (NC(OH)) and in the subsequent step crystalline NiCo2O4 (NCO) has been produced using water as the solvent. For nickel-zinc batteries, NC(OH) was found to have superior performance to its NCO prepared by two-step process. The thermal stability analysis exhibited the optimum temperature to obtain the NC(OH), and NCO electrode materials. The XRD pattern showed mixed phases containing both Ni and Co hydroxides (during the initial step) and in the subsequent step (calcined) the formation of cubic spinel structure was noticed. For NC(OH), aggregated particles with irregular morphology were observed while clustered nanorod-like shapes were noticed for NCO samples. To be noted, that the nanorod morphology was obtained through a facile approach without employing any structure-directing agent. Both NC(OH) and NCO were employed as cathodes for Ni−Zn battery studies against Zn foil anode with a polyamide-based separator soaked in 6 M KOH saturated with ZnO additive was used as electrolyte. The Ni−Zn cell was fabricated in CR2032 coin cell configuration. The electrochemical studies such as cyclic voltammetry (CV) showed the characteristic redox peaks for NC(OH) sample exhibiting high peak current compared to its NCO counterpart. The NC(OH) had a capacity of 268 mAh g−1 against 120 mAh g−1 for NCO at a current density of 1 Ag−1. The cell was able to retain 85 % of the capacity at the end of 500 cycles and showed remarkable rate capability. The Ni−Zn battery presents energy and power densities of 428.8 Wh Kg−1 and 2.68 kW Kg−1, respectively surpassing the normal values reported for aqueous rechargeable batteries. Owing to the presence of Ni and Co in hydroxide form (reduced crystallinity) the NC(OH) sample showed improved electrochemical activity. This work provides a facile approach and effective strategy for developing bimetallic hydroxides for optimal energy storage performance.