Publication: Nano-architectures with hierarchical porosity manufactured by colloidal techniques for application in ceramic semiconductor-based supercapacitors
Loading...
Identifiers
Publication date
2019-07
Defense date
2019-09-16
Authors
Tutors
Journal Title
Journal ISSN
Volume Title
Publisher
Impact
Export
Abstract
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. 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.
Description
Mención Internacional en el título de doctor
Esta tesis contiene artículos de investigación en anexo
Esta tesis contiene artículos de investigación en anexo
Keywords
Supercapacitors, Ceramic semiconductors, Energy-efficient storage devices, Colloidal techniques, Nanotechnology