Characterisation of novel electrode materials for renewable energy storage application

Increasing requirements for renewable energy supply have pushed forward the development of low-cost, high-performance energy storage systems. Supercapacitors are a promising alternative to traditional electrochemical battery power storage devices as they have high power and energy densities and long cycle lives. Binary transition metal oxides (BTMOs) have been investigated as promising materials to improve supercapacitors as they can harness both faradaic and non-faradaic mechanism for energy storage and may exhibit improved conductance compared to simple metal oxides. The combination of these parameters leads to materials that can deliver superior capacitance, long cycling life, and good rate performance. Energy storage mechanisms in electrochemical devices are primarily surface reactions and maximising the available surface area for electrode/electrolyte interaction should improve storage capacity. As such, being able to create a porous electrode material with a suitable pore size distribution should improve the electrochemical performance of supercapacitors. The main aim of this work was to use polymeric templates to synthesise porous binary transition metal oxides (BTMOs) as a way of improving the specific capacitance of materials that could be used to construct supercapacitor electrodes. Novel, porous BTMO materials (NiMoO4, NiCo2O4, CoMoO4 and NaNiVO4) were synthesised using Egg-Shell Membrane (ESM) and poly(methylmethacrylate) (PMMA) using simple, one-pot hydrothermal combustion techniques. The synthesised materials were physically and electrochemically characterized. Addition of a template to the synthesis procedure resulted in improved performance compared to non-templated material for NiMoO4, NiCo2O4, and CoMoO4. In particular, use of the ESM template resulted in significant improvements in performance of the molybdates. The ESM templated NiMoO4 had the best performance with a measured specific capacitance 259 F.g-1 (2-electrode system) with an energy density of 252.2 Whkg-1. The ESM template seemed to promote the formation of β-NiMoO4, a crystal structure that has superior electrochemical storage properties compared to other isomorphs. This was achieved with relatively mild synthesis conditions and resulted in a material that had a porous structure consisting of nanowire like particles. This open, fibrous structure increased available surface area and accessibility to the interior of the bulk material. Optimal choice of polymeric template may need to be tuned to the final product as the best specific capacitances for CoMoO4 (74.45 F.g-1) and NiCo2O4 (38.03 F.g-1) were achieved using different templates; ESM for the former and PMMA for the latter. Synthesis of a novel material, NaNiVO4, was attempted but the resulting material was not fully characterised due to poor performance during initial electrochemical testing

Polymer templated nickel cobaltate for energy storage

In order to take advantage of the increasing sophistication of technology for harnessing renewable energy resources, serious attention must be paid to how to store and re-access this energy. Electrochemical storage, in the guise of batteries, supercapacitors and pseudocapacitors, has attracted much attention as a viable option for enhanced energy storage applications. But in order for these technologies to be implemented successfully we need to find materials that perform better and are relatively easy to synthesise. Bimetallic transition metal oxides are materials that are readily synthesised and may be multifunctional, i.e. have a role at the electrochemical atomic level as well as the device level. In order for these materials to work efficiently in new generation systems based on sodium and lithium they also need to be mesoporous. This can be achieved by trying to find synthetic techniques that produce specific, highly regulated nanostructures or by adding a ‘templating’ agent during the bulk synthesis step. We have investigated the simple hydrothermal preparation of a number of nickel cobaltate (NiCo2O4) materials using polymer templates, eggshell membrane (ESM) and poly methyl methacrylate (PMMA), as potential electrode materials for supercapacitors. The ESM was expected to act as a fibrous, random polymeric template while the PMMA should produce a much more ordered material. Electrochemical testing showed that the different templates have led to changes in material morphology and these have resulted in a difference in electrochemical properties. Templated materials had an increased specific capacitance than non-templated and the choice of template could influence the capacitance by as much as 30 %

Do porosity templates improve the performance of supercapacitor electrode materials?

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Egg shell membrane template stabilises formation of β-NiMoO4 nanowires and enhances hybrid supercapacitor behaviour

Adding an eggshell membrane (ESM) template to the solution combustion synthesis of NiMoO4 resulted in the formation of β -NiMoO4 under mild conditions. It is postulated that the unique nature of the ESM template results in interactions that stabilise this difficult to synthesise form of NiMoO4.The ESM template led to β -NiMoO4 particles that were nano-wire like in shape and arranged in an open weave structure that significantly enhanced the mesoporosity and conductance of the material. The specific capacitance was measured as 259 F g-1 in a two electrode system with an energy density of 252.2 W h kg-1. The results indicate that the use of a fibrous like natural polymeric materials as templates stabilises materials in preferred crystal forms and shapes leading to much improved electrochemical performance

Egg shell membrane templated nickel molybdate for supercapacitor electrodes

Poster presentatio

Polymer templated nickel cobaltate for energy storage★

In order to take advantage of the increasing sophistication of technology for harnessing renewable energy resources, serious attention must be paid to how to store and re-access this energy. Electrochemical storage, in the guise of batteries, supercapacitors and pseudocapacitors, has attracted much attention as a viable option for enhanced energy storage applications. But in order for these technologies to be implemented successfully we need to find materials that perform better and are relatively easy to synthesise. Bimetallic transition metal oxides are materials that are readily synthesised and may be multifunctional, i.e. have a role at the electrochemical atomic level as well as the device level. In order for these materials to work efficiently in new generation systems based on sodium and lithium they also need to be mesoporous. This can be achieved by trying to find synthetic techniques that produce specific, highly regulated nanostructures or by adding a ‘templating’ agent during the bulk synthesis step. We have investigated the simple hydrothermal preparation of a number of nickel cobaltate (NiCo2O4) materials using polymer templates, eggshell membrane (ESM) and poly methyl methacrylate (PMMA), as potential electrode materials for supercapacitors. The ESM was expected to act as a fibrous, random polymeric template while the PMMA should produce a much more ordered material. Electrochemical testing showed that the different templates have led to changes in material morphology and these have resulted in a difference in electrochemical properties. Templated materials increased specific capacitance compared to non-templated and the choice of template could influence the capacitance by as much as 30%

Spray pyrolysis synthesis and characterization of Mg1-xSrxMoO4 heterostructure with white light emission

[EN] Molybdates are inorganic materials with great potential in white phosphors application, being an alternative to traditional lighting sources. In this study, we report the synthesis and characterization of Mg1-xSrxMoO4 (x = 0, 0.25, 0.50, 0.75, and 1) powders with white light-emitting properties. Using X-ray diffraction, the formation of the monoclinic beta-MgMoO4 phase was observed for x = 0 and the formation of the tetragonal scheelite phase of SrMoO4 was observed for x = 1. The formation of a heterostructure composed of both phases was found for compositions with x = 0.25, 0.50 and 0.75. Scanning and trasmission electron microscopy images showed that the Mg1-xSrxMoO4 particles exhibit a spherical morphology formed by several primary nanoparticles. Raman scattering spectroscopy enabled the accurate identification of the Raman modes for different compositions and their assignment to either the SrMoO4 or beta-MgMoO4 modes. The bandgap energies were determined to fluctuate between 4.25 eV and 4.44 eV, being influenced by the degree of structural disorder. The photoluminescence emission spectra of the nanoparticles showed neutral- and cool-white emission with high-quality white light (CRI > 80%). The samples synthesized with x <= 0.50 are potential materials for the application in LED lamps (6500 K) and pure white-light sources (5500 K).The authors thank the following Brazilian and Spanish research financing institutions for financial support: A.A.G. Santiago acknowledges financial support from the National Council for Scientific and Technological Development -CNPq, the Graduate Program in Materials Science and Engineering (PPGCEM-UFRN) and the Coordination for the Improvement of Higher Education Personnel (CAPES) -Brazil (CAPES) -Finance Code 001. F.J.M. and D.E. acknowledge financial support from the Spanish Ministerio de Ciencia, Innovacion y Universidades, the Spanish Agencia Estatal de Investigacion (AEI), and the Fondo Europeo de Desarrollo Regional (FEDER) under Grants No. MAT2016-75586-C4-1/2-P and from the Generalitat Valenciana under Grant Prometeo/2018/123 - EFIMAT.Santiago, AAG.; Tranquilin, RL.; Botella, P.; Manjón, F.; Errandonea, D.; Paskocimas, CA.; Motta, FV.... (2020). Spray pyrolysis synthesis and characterization of Mg1-xSrxMoO4 heterostructure with white light emission. Journal of Alloys and Compounds. 813:1-13. https://doi.org/10.1016/j.jallcom.2019.152235S113813Gao, Z., Sun, P., Zhong, Y., Yu, R., & Deng, B. (2019). Eu3+-doped highly thermal-stable barium yttrium aluminate as a red-emitting phosphor for UV based white LED. Optics & Laser Technology, 111, 163-168. doi:10.1016/j.optlastec.2018.09.026Zhong, J., Chen, X., Chen, D., Liu, M., Zhu, Y., Li, X., & Ji, Z. (2019). 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