With the continued demand for sustainable alternative energy fuels to replace limited fossil fuels, it is essential to explore new material properties to attain a zero-carbon emission
economy. Porous metallic materials possess attractive properties for electrochemical storage and
energy conversion such as superior surface area, high conductivity and large open volume,
facilitating the mass transport of guest molecules.
Among the different electrochemical energy storage applications, lithium metal batteries
have been a competitive candidate for the next-generation of batteries. Despite its popularity,
stability issues of lithium metal anode in the liquid electrolyte and the formation of lithium
whiskers have kept it from practical use. Furthermore, finding scalable catalyst materials to
electrochemically reduce carbon dioxide (CO2R) to multi-carbon products such as ethylene and
ethanol is key for a promising pathway to a carbon-neutral economy.
The objective of this thesis is to utilize porous metallic copper for electrochemical
applications including (1) macroporous Cu as current collectors for Li metal batteries and (2)
mesoporous Cu as a catalyst for higher-reduced products for CO2 reduction.
The first part of this thesis proposes three-dimensional (3D) macroporous Cu current
collectors as an effective method to mitigate whisker growth during the Li deposition process in
a lithium metal battery (LMB). Three key parameters of the 3D current collectors, namely, the
surface area, the tortuosity factor, and the surface chemistry are quantitatively studied to
optimize the performance of these current collectors for LMB applications. Four types of porous
copper networks with different sizes of well-structured microchannels are synthesized and
electrochemically tested. It is found that a moderate surface area that can lower the current
density of Li deposition while minimizing the formation of SEI is ideal to suppress lithium
whisker growth and optimize performance. Furthermore, tortuosity should be kept at minimum
in order to facilitate Li diffusion and lead to a more uniform Li morphology. In considering these
parameters, it was determined that the 20Arc Cu sample (~14um average pore size) with a
balance of moderate surface area and reasonable pore size had the best performance of all Cu
samples tested. Lastly, a lithiophilic Zn layer is coated on the best and worst performing current
collectors (~14�m and ~30�m average pore sizes, respectively). It is shown that Zn coating can
improve the Li morphology and the coulombic efficiency from 99.16% to 99.56% for a low
surface area 3D current collector.
Chapter 3 is a follow-up study of Chapter 2 with a focus on strategies to increase the
lifetime cycling of the current collectors via asymmetric lithiophilic Ag coating. For this
purpose, 3D porous Cu frameworks of 10 �m (30-Cu) and 14 �m (20-Cu) average pore sizes
were used. Unfortunately, Li deposition on these structures is generally top-favored, increasing
the chances for dendrite formation. To overcome this issue, a lithiophilic Ag coating with
gradient composition, gradually decreasing from the bottom to the top of the framework, was
utilized on these 3D Cu structures to favor Li deposition at the bottom of the porous network.
By comparing the coulombic efficiency (CE), stability, and lifetime of these asymmetrically
against both uncoated and symmetrically coated samples, it was found that the lifetime and CE
of the current collectors can be increased. Particularly, the 20-Cu sample improved its lifetime by
30% and 10% at 2mA/cm2 (10mAh/cm2) and 4mA/cm2 (10mAh/cm2) current rates, respectively.
This was corroborated with post-cycling SEM images that showed a more ‘bottom-favored’
deposition and denser Li morphology on the asymmetrically coated samples.
The last part of the thesis focuses on the development of scalable mesoporous Cu catalyst
materials to electrochemically reduce carbon dioxide (CO2R) to multi-carbon products such as
ethylene and ethanol. This work utilizes a scalable method of making powdered mesoporous Cu
samples with dilute amounts of Al via dealloying of Cu-Al alloys with different compositions
(10-22 at. % Cu). Dealloying produced mesoporous-macroporous Cu powdered structures with
composition-dependent microstructure. These samples were electrochemically tested as catalysts
for CO2 reduction in a membrane electrode assembly. Tuning the catalyst pore size distribution
increased overall CO2R current density and C2+ selectivities. Tandem catalytic enhancement was
also observed through dilute amounts of secondary metal coating, with the presence of a silver
coating increasing C2+ reaction rates by up to 23.3%, and combined ethylene/ethanol production
by up to 14.8% at a 500mV lower potential.
Through the results in this work, we hope to contribute to the strategies for design and
optimization of porous materials for current collectors in lithium metal batteries as well as the
importance of synergistic optimization of catalyst pore architecture and chemical composition in
CO2R catalyst design to enhance the production valuable products.