Nano-architectures with hierarchical porosity manufactured by colloidal techniques for application in ceramic semiconductor-based supercapacitors

Mención Internacional en el título de doctorEsta tesis contiene artículos de investigación en anexoAll the scientific contributions presented in this thesis have a main goal: to achieve science and technology challenges in the manufacture of energy storage devices based on a ceramic semiconductor employing colloidal processing strategies. Needs of the renewable energy systems and portable devices have revolutionized research on energy storage systems. Development of more powerful devices able to store large amounts of energy is now the challenge. In this field, the research in supercapacitors (SC) based on ceramic semiconductors has been tackled as a relevant issue to improve the electrochemical response of the electrodes inducing better reactant–catalyst contacts through the design of complex structures with large surface-to-volume ratio. The structuring and electrochemical activity of the pseudocapacitors (PCs) electrodes can be controlled by tuning the physical properties of the electroactive material (particle size, crystalline phase, preferred orientation) but also, shaping and consolidating the ceramic microstructure (publication 1). As a promising electroactive material (and non-strategic raw material), the NiO presents an elevated theoretical capacitance, high thermal and chemical stability and easy availability (publication 1). For these reasons, in this research work, he ultrasound aided synthesis of Ni(OH)2 and NiO nanoplatelets was standardized, and the manufacture of tridimensional (3D) and bidimensional (2D) NiO-based electrodes for PCs was tackled throughout different colloidal processing strategies. The Electrophoretic Deposition (EPD) and inkjet printing (IJP) technologies have been employed as shaping techniques for the manufacturing of these electrodes. While EPD allows us to fully and homogeneously coating collectors with complex shapes, as 3D Ni foams, the IJP enables the miniaturization of 2D electrodes for their use in energy-storage microdevices (publication 5). Both techniques are based on the dispersion and stabilization of Ni(OH)2 and NiO nanoplatelets in colloidal water-based suspensions, which were optimized for each application, leading to PC electrodes with specific capacitances of 250 and 160 F/g with retentions of 71 and 100%, respectively, where the remarkable low charge transfer resistance (Rct = 0.23Ω) of NiO patterns (IJP) has to be highlighted. Moreover, the assembly of synthesized NiO nanoplatelets has been also addressed resulting in a cohort of semiconductor microarchitectures that improves the electrochemical response of PC electrodes shaped by EPD. EPD is a well-known colloidal technique with remarkable performance in the coating of electrodes with complex shapes. However, for PC electrodes shaping, the nature and shape of the substrate have to be considered since collector has a relevant influence on electron transfer phenomena as well as the ion diffusion at the electrode/electrolyte interface (publication 4 & 7). The deposition and consolidation of the electroactive nanoplatelets through a mild heat treatment (sintering) connects the particles by the formation of sintering necks reducing Rct of these 3D electrodes to 1.71Ω. (publication 2 & 7). To cover Ni-3D collectors improving electrochemical performance, one of the employed colloidal strategies in this thesis was the surface modification of NiO nanoplatelets by layer-by-layer deposition of polyelectrolytes, leading to the formation of organic/inorganic core-shell structures which strongly modified the NiO nanoplatelets assembly by EPD (publication 3). The resulting hierarchical nanostructure presents high Rct values (3.65 Ω), while the capacitive response (CPE-p = 0.90) step up due to the enhancement of electrolyte wetting and faster ion diffusion. This fully ceramic porous nanostructure shows a specific capacitance of 982 F/g, with 60% retention after 1000 cycles, and relaxation times in the rage of carbonaceous SC electrodes (τ0 = 18 s), demonstrating that the capacitance is strongly related to the surface exposure of the semiconductor to the electrolyte, in spite of a relative high Rct. This is because of the increase in resistance is compensated by a better capacitive behavior as well as a better rate capability (publication 7). Finally, we also demonstrate that Rct can be reduced by the inclusion of materials capable of sharing their free electrons within the semiconductor microstructure such as metallic Ni or reduced graphene Oxide (RGO) (publication 2, 6 & 7), without deteriorating the capacitive response. In this way, NiO/Ni electrodes with specific capacitances of 755 F/gr and a retention of 71% was shaped by EPD in Ni foams, leading to Rct values of 1.55Ω and relaxation times of 11 s; while RGO/NiO hybrid supercapacitors (HSC) were prepared also by EPD, exhibiting specific capacitances of 920 F/g at a current density of 2 A/g with a retention of 71% and a Rct as low as 1.13Ω and a relaxation time of 4 s.Programa de Doctorado en Ciencia e Ingeniería de Materiales por la Universidad Carlos III de MadridPresidente: María Eugenia Rabanal Jiménez.- Secretario: Jadra Mosa Ruiz.- Vocal: Sandra Cabañas Pol

In Situ Synthesis and Electrophoretic Deposition of NiO/Ni Core-Shell Nanoparticles and Its Application as Pseudocapacitor

A simple, low cost and transferable colloidal processing method and the subsequent heat treatmenthasbeenoptimizedtopreparebinder-freeelectrodesfortheirapplicationinsupercapacitors. NiO/Ni core–shell hybrid nanostructures have been synthetized by heterogeneous precipitation of metallic Ni nanospheres onto NiO nanoplatelets as seed surfaces. The electrophoretic deposition (EPD) has been used to shape the electroactive material onto 3D substrates such as Ni foams. The method has allowed us to control the growth and the homogeneity of the NiO/Ni coatings. The presence of metallic Nickel in the microstructure and the optimization of the thermal treatment have brought several improvements in the electrochemical response due to the connectivity of the final microstructure. The highest specific capacitance value has been obtained using a thermal treatment of 325◦C during 1 h in Argon. At this temperature, necks formed among ceramic-metallic nanoparticles preserve the structural integrity of the microstructure avoiding the employment of binders to enhance their connectivity. Thus, a compromise between porosity and connectivity should be established to improve electrochemical performance

Nano-architectures with hierarchical porosity fabricated by colloidal techniques for their application in supercapacitors based on ceramic semiconductors

[EN] All the scientific contributions presented in this thesis have a main goal: to achieve science and technology challenges in the manufacture of energy storage devices based on a ceramic semiconductor employing colloidal processing strategies. Needs of the renewable energy systems and portable devices have revolutionized research on energy storage systems. Development of more powerful devices able to store large amounts of energy is now the challenge. In this field, the research in supercapacitors (SC) based on ceramic semiconductors has been tackled as a relevant issue to improve the electrochemical response of the electrodes inducing better reactant–catalyst contacts through the design of complex structures with large surface-to-volume ratio. [...]Esta tesis contiene artículos de investigación en anexo: http://doi.org/10.3390/coatings7110193; http://doi.org/10.1016/j.electacta.2017.07.043; http://doi.org/10.1149/08201.0097ecst; https://doi.org/10.1016/j.jeurceramsoc.2019.03.020; https://doi.org/10.1016/j.electacta.2019.04.053; http://doi.org/10.1149/2.0341905jesPeer reviewe

Understanding the effects of different microstructural contributions in the electrochemical response of Nickel-based semiconductor electrodes with 3D hierarchical networks shapes

[EN] It is well known that exposed surface area, nanoparticles connectivity and its consolidation level in a nanostructure are key points in the enhancement of the electrochemical performance in energy storage devices. The design and optimization of different electrodes with specific microarchitectures (based on the arrangement manipulation of NiO nanoplatelets, used as building blocks), has allowed distinguishing the effects of each microstructural contribution in their final electrochemical responses, overpassing thermal and mechanical mismatches between the semiconductor ceramic structure and the metallic collector. In all cases, the same electroactive material and the same coating technique were used, preventing the interference of secondary phenomena in the EIS studies, and allowing argue over the contribution of the microstructural features incorporated to the electrode (nature and shape of the collector, degree of sintering and consolidation of the ceramic microstructure, incorporation of non-noble metallic nanoparticles and the macro/meso/microposity effect) in the effective profiting of the Faradaic phenomena observed during their cycling. The modification of the Ni-based electrodes allows understanding how microstructural features infer the electron transport and the ion diffusion through the consolidated structure. The EIS analysis proves that the design of the porous hierarchical network of our semiconductors electrodes resulted in a good rate capability (with capacitance values of 1000 F g¿1 or 500 C g¿1), exhibiting a relaxation time constant (¿0 = 18 ms), while a slight increase of the charge-transfer resistance (Rct = 3.65¿) is negligible if the exposed surface is high enough to maintain a high ion transport. The inclusion of non-noble nanoparticles, such as Ni NPs, in the NiO semiconductor microstructure and the optimum deposited mass and sintering treatment create a metal-ceramic electrode that enhances both the charge transfer resistance (1.55 ¿) showing relaxation time in the range (¿0 = 11 ms) and maintaining an excellent capacitive behavior (750 F g¿1 or 375C g¿1) at quick charge/discharge rate.2018/NMT-4411(Comunidad de Madrid, Spain) and MAT2015-70780-C4-1(MINECO/FEDER, Spain). J. Yus acknowledges the Comunidad de Madrid for the support from the Youth Employment Initiative,CAMPD17_ICV_002. Z. Gonzalez acknowledges the Postdoctoral Fellowship: IJCI-2016-28538 (MINECO, Spain

Flavonols in skins of wild grapes (

Flavonols are a group of grape phenolics that play an important role in young red wines, as they are involved in copigmentation of the flavylium form of anthocyanins. A study on the flavonol composition of grape skins in several wild grapevine genotypes from different Iberian natural populations, preserved at El Encin Germoplasm Bank, has been carried out in 2012. Flavonol glycosides contained in grape skins were determined by HPLC-DAD and HPLC-MS, through a previous phase of purification, using ion exchange chromatographic columns to retain anthocyanins and other phenolic compounds, so that flavonols do not suffer co-elution with other components, improving HPLC analysis. Thus, it was possible to separate 12 flavonol glycosides, and eight of them were successfully identified. The major flavonols were quercetin-3-O-glucoside, quercetin-3-O-glucoronide and myricetin-3-O-glucoside. The diversity and number of flavonols differed for each genotype. The total content of flavonols ranged from 25 to 350 mg/kg grapes; the richest genotype was three times richer than Tempranillo grapes, used as a reference. The most significant difference between wild genotypes and reference cultivars was that, in many cases, myricetin-3-O-glucoside or quercetin-3-O-glucuronide predominated in wild genotypes

Exploitation of Lignocellulose Fiber-Based Biotemplates to Improve the Performance of an Immobilized TiO2 Photocatalyst

The performance of an immobilized photocatalyst has been successfully improved by colloidal processing of a heterostructure composed by TiO2 nanoparticles and lignocellulose nanofibers (LCNFs) obtained from biomass residues. The incorporation of 4 wt.% of biotemplate to the formulation increased the degradation rate and reduced the operating time to remove the 100% of methyl orange of a liquid solution. The reaction rate constant (k = 0.29–0.45 h−1) of the prepared photocatalytic coatings (using commercial particles and templates obtained from natural-derived resources) are competitive with other pure TiO2 materials (no composites), which were prepared through more complex methodologies. The optimization stages of deposition and sintering processes allowed us to obtain homogeneous and crack-free microstructures with controlled thickness and mass values ranging from 3 to 12 µm and 0.9 to 5.6 mg, respectively. The variation of the microstructures was achieved by varying the amount of LCNF in the formulated suspensions. The versatility of the proposed methodology would allow for implementation over the internal surface of photocatalytic reactors or as a photocatalytic layer of their membranes. In addition, the processing strategy could be applied to immobilize other synthetized semiconductors with higher intrinsic photocatalysis properties.This research was supported by the projects S2018/NMT-4411 (Comunidad de Madrid) and PID2019-106631GB-C42 (MINECO/FEDER). Z. Gonzalez acknowledges the Spanish Ministry of Economy and Competitiveness for the Postdoctoral Fellowship: IJCI-2016-28538.This work was supported by FCT-Fundação para a Ciência e a Tecnologia (project PEst-OE/QUI/UI0674/2019, CQM, Portuguese government funds), through the Madeira 14–20 Program, project PROEQUIPRAM Reforço do Investimento em Equipamentos e Infraestruturas Científicas na RAM (M1420-01-0145-FEDER-000008) by ARDITI-Agência Regional para o Desenvolvimento da Investigação Tecnologia e Inovação, through project M1420-01-0145-FEDER-000005—Centro de Química da Madeira CQM + (Madeira 14–20). SM was supported by the postdoctoral fellowship granted by ARDITI CQM + project (ARDITI-CQM/2017/008-PDG). RP was supported by an FCT postdoctoral grant (SFRH/BPD/97387/2013).Peer reviewedPeer reviewe

Electrophoretic deposition of RGO-NiO core-shell nanostructures driven by heterocoagulation method with high electrochemical performance

A heterocoagulation route is proposed to prepare Reduced Graphene Oxide-Nickel Oxide (RGO/NiO) hybrid structures for their application as supercapacitor electrodes. The RGO intercalation among the NiO nanoplatelets was carried out by electrostatic interactions of the synthetized particles which were previously dispersed and stabilized in aqueous media to improve the assembly between both materials forming core-shell structures. The electrophoretic deposition (EPD) was used to shape the composite onto 3D collector (Ni foams) controlling their growth and homogeneity. Electrodes were thermal treated at 325 °C during 1 h to improve the electrochemical response since the formation of ceramic necks among NiO semiconductor nanoparticles preserves the microstructural integrity to enhance their connectivity avoiding the employment of binders, while RGO contributes with the electrochemical double layer effect to step up the specific capacitance by reducing the charge transfer resistance. FESEM results confirmed that RGO nanosheets were full-covered by the NiO nanoplatelets and suggested that ∼1 mg of the electroactive composite homogeneously covers the Ni foam and it is the optimum among of electroactive material to avoid microstructural defects that produce ohmic drops limiting the capacitance. The electrochemical characterization of the resulting binder-free RGO/NiO electrodes was compared with the bare-NiO electrode. The hybrid composite exhibited excellent performance with a high specific capacitance of 940 FThe authors thank the support to the projects S2018/NMT-4411 (Comunidad de Madrid) and MAT2015-70780-C4-1 (MINECO/FEDER). J. Yus acknowledges the Comunidad de Madrid for the support from the Youth Employment Initiative, CAMPD17_ICV_002. Z. Gonzalez acknowledges the Postdoctoral Fellowship: IJCI-2016-28538.Peer Reviewe

Colloidal processing and sintering of WC-based ceramics with low Ni content as sintering aid

To soften the extreme sintering conditions of Tungsten Carbide (WC), a 3 wt.% of metallic nickel (Ni) was added to the starting powders. To ensure a fair distribution of the second phase and an intimate mixture of the phases, the colloidal process was adopted. A commercial Ni and a in-house synthesised nanosized nickel were used as sintering aids. Rheological studies allowed a high dispersion of the nickel in the final composite powders. Sintering studies by Hot-Pressing route (HP) proved the great benefices of Ni as a sintering aid, decreasing the maximum temperature necessary to achieve full densification, from 1900 to 1450 °C and dwell times from 20 to 7 min. Among all the materials obtained, the best results in terms of density, microstructure and properties were obtained for WC-nNi, which achieved hardness of 14.8 GPa and toughness comparable to conventional cermets with much higher content of metallic phase.This work has been supported by the Spanish Government under contracts PID2019-106631GB-C42 and C44 (MICINN/FEDER, UE) and Madrid Regional Government under contract P2018/NMT-4411 (Comunidad de Madrid/FEDER, UE). Mrs. García-Ayala thanks MINECO/FEDER, UE by grant BES-2016-079038 and JECS Trust for a mobility grant (ref: 2018170) for three months to ISTEC. Authors thank A. Sangiorgi for advice and support running the HP cycles

Electrochemical performance of pseudo-capacitor electrodes fabricated by Electrophoretic Deposition inducing Ni(OH)2 nanoplatelets agglomeration by Layer-by-Layer

The electrochemical behaviour of ceramic semiconductors not only depends on the characteristics of the electroactive material but also on the processing method, the nanoparticles arrangement and the consolidation degree of the formed microstructure. In this sense, the use of nanoparticles with plane morphologies (disc, platelets, etc.) results interesting due to the formation of conduction pathways produced as a consequence of their laminar structures. Electrophoretic Deposition (EPD) is a shaping methodology which allows achieving high degrees in nanoplatelets packing by controlling their alignment during the coating process specifically over 3D substrates. In this work, we have studied the effect of a moderate nanoplatelets agglomeration, by tuning their surfaces with a polyelectrolyte multilayer following a Layer-by-Layer (LbL) methodology and fixing the electric conditions of the EPD process. Overcoming the destructive effects of the full agglomeration of nanoplatelets, NiO films with a stable and extremely open macroporous structure were processed to coat Ni foams, improving the capacitive performance of pseudocapacitors leading to values of specific capacitances of 650 F/g. Results collected in this work also evidence that an efficient ordering and orientation of nanoplatelets in EPD mainly depends on tuning the suspension parameters (solid contents, conductivity, electrophoretic mobility, etc.) to avoid the massive flux and interactions among interparticles and electro-hydrodynamic forces, as well as the interference of collateral electrode phenomena.The authors acknowledge the support of the project S2013/MIT-2862 and MAT2015-70780-C4-1 and Dr. Z Gonzalez acknowledges to JECS-TRUST fund contract 201481.Peer Reviewe

3D Printing of Photocatalytic Filters Using a Biopolymer to Immobilize TiO2 Nanoparticles

Titanium oxide-based photocatalytic filters were produced by Fused Deposition Modelling (FDM) using biopolymers obtained from renewable biomass resources. The thermoplastic route allows shaping composites through the immobilization of photoactive TiO2 nanoparticles in an environmentally friendly bioplastic such as the polylactic acid (PLA). Composites with an inorganic charge of 30 wt% of TiO2 nanoparticles (NPs) exhibit a 100% methyl orange (MO) degradation after 24 h of light exposition due to the extremely uniform dispersion of the nanophase within the polymer matrix in the FDM feedstock. Surface modification of TiO2 NPs allows the optimization of the colloidal dispersion and stabilization of the inorganic charge in a PLA solution and hence, the optimal distribution of nano-photoactive points in the TiO2/PLA filaments and scaffolds. The proposed new route of processing improves the dispersion of nano-charges comparing with the traditional thermo-pressing routes used for mixing thermoplastics based composites, avoiding the thermal degradation of the polymer and providing a customised product. In this manuscript the evolution of photodegradation with the increase of TiO2 content in the composite and the variation of the filter geometry was evaluated.Authors acknowledge the support to the projects S2018/NMT-4411 (Comunidad de Madrid) and MAT2015-70780-C4-1 (MINECO/FEDER). Z. Gonzalez acknowledges the Spanish Ministry of Economy and Competitiveness for the Postdoctoral Fellowship: IJCI-2016-28538. J. Yus acknowledges to the Comunidad de Madrid the support from the Youth Employment Initiative, CAMPD17_ICV_002. The authors thank ECERS for funding on Mobility Project JECS Trust Contract number: 2017294.Peer Reviewe