bluuebunny/crossref_metadata_2025 huggingface dataset:
3D Structured Pt(Cu-Ni)/Ti Catalysts for the Oxidation of Sodium Borohydride
Authors: Balciunaite Aldona , Činčienė Žana , Tamasiunaite Loreta , Vaičiūnienė Jūratė , Norkus Eugenijus
Published: July 2022

Currently, one of the renewable energy sources is fuel cells, namely chemical energy is directly converted into electricity. Designing new or enhancing the existing fuel cells, much attention is devoted to the search of new effective catalysts, which would allow increasing the effectiveness of fuel cells and creating the background for designing new technologies for catalysts formation.

The aim of the work is to form efficient and inexpensive nanostructured catalysts by electroplating 3D structure metal copper-nickel (Cu-Ni) foams on titanium (Ti) surface and decorating them with low amounts of platinum nanoparticles (PtNP) for the electrooxidation of sodium borohydride (NaBH4). The Cu-Ni foam was prepared by electrochemical deposition (I
deposition=1.5 Acm-2, t
deposition= 3,6 and 9 min) on Ti surface. The electrolyte contained 0.5 M Ni2+ ions, and the concentrations of Cu2+ ions ranged from 0.01 to 0.02 M.

PtNP particles were deposited on Cu-Ni foam (noted (Pt(Cu-Ni)/Ti)) by immersion of Cu-Ni foam into 1 mM H2PtCl6 solution at 25 °C for 1 minute. The morphology and composition of the prepared catalysts were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and inductively coupled plasma optical emission spectroscopy (ICP-OES). The electrocatalytic activity of the 3D catalysts was evaluated towards the oxidation of borohydride by cyclic voltammetry method in 0.05 M NaBH4 solution in an alkaline media in the potential range from -1.2 to 0.6 V (vs. Ag/AgCl) and with an electrode potential scan rate of 10 mVs-1.

The study showed that the prepared 3D Cu-Ni foam and Pt(Cu-Ni)/Ti have good electrochemical stability in alkaline NaBH4 solution. It was also observed that immersion of Cu-Ni foam in a platinum-containing solution for 1 min increased the electrocatalytic activity of the prepared Pt(Cu-Ni)/Ti catalysts for NaBH4 oxidation compared to Cu-Ni foam.

Acknowledgment

This project has received funding from European Social Fund (project No 09.3.3-LMT-K-712-19-0138) under a grant agreement with the Research Council of Lithuania (LMTLT).
Transition Metal Doped Cannabis Catalysts for the Oxygen Reduction Reaction in Hydrogen Fuel Cells
Authors: Rana Zahra Imran , Feng Jingyu , Magliocca Emanuele , McAlernon Patricia , Miller Thomas Samuel , Titirici Magda , Brett Dan
Published: July 2022

The global climate crisis demands a rapid uptake of alternatives to fossil fuels to alleviate further damage to the planet. To this end, supercapacitors, batteries and fuel cells have been identified as critical enabling technologies to overhaul the current energy system. As the demand for these energy storage and conversion devices increases, so does the need to produce sustainable, low-cost and high-performing components for them.

Currently, platinum is used to catalyse the sluggish oxygen reduction reaction (ORR) in hydrogen fuel cells. It is generally deposited on a carbon support and forms an electrode that is vital in determining electrochemical performance (namely activity and durability); however, this presents a two-pronged challenge. Traditionally, the carbon used is synthesised via energy-intensive and time-consuming processes involving the incomplete combustion of heavy petroleum products or coal. Secondly, platinum scarcity lends to issues of high cost, which is often ascribed to being the largest hindrance in large-scale commercialisation of this technology. To mitigate these issues, an electrocatalyst based on transition metals and a biomass precursor can be effectively used instead.1

A very promising biomass precursor is hemp. Also known as industrial hemp, it is one of two strains of the cannabis plant. It is one of the oldest domesticated crops in the world, known for its sustainability, high yield and ability to grow on marginal land with low water and pesticide requirements. It is carbon-negative, low-cost and biodegradable - making it the ideal choice in the current climate crisis. Through thermal carbonisation and activation, it yields 3-dimensional hierarchical structures with high conductivity, surface area and porosity.2

Here we report on using nitrogen, iron and cobalt together with cannabis-derived carbon to produce a high functioning and low-cost electrocatalyst to replace Pt/C at the cathode, as shown by a suite of characterisation and electrochemical techniques. With a uniform mesoporous texture and good distribution of metal species, the material displays properties beneficial to catalysing the ORR with a much lower environmental and monetary cost than traditional Pt/C. This forms an excellent basis for further work in this field to achieve the overarching goals of high performance coupled with environmental sustainability.

Borghei M., Lehtonen J., Liu L. and Rojas O. J. 2018 Advanced Biomass-Derived Electrocatalysts for the Oxygen Reduction Reaction. Adv. Mater.
30 1703691

Rana Z. I., Shah A. R., Llewellyn A. V., Mazloomian K., McAlernon P., Miller T. S., Cullen P. L., Shearing P.R. and Brett D. J. L. B. 2022 A new high: Cannabis as a budding source of carbon-based materials for electrochemical power sources. Curr. Opin. Electrochem.
31 100860
(Invited) CdS/Pd Photocatalytic Bipolar Membrane for Selective Reduction and Oxidation Processes
Authors: Kamat Prashant V , Costantino Federica
Published: July 2022

A bipolar membrane with specific cation exchange and anion exchange properties between the two layers enables design of photocatalytically active membrane which also separate reaction compartments. The key advantage of such a membrane lies in the separation of oxidation and reduction processes while continue to engage in the photodriven reactions. The example of simultaneous oxidation of 4-chlorophenol and the reduction of 4-nitrophenol under visible light irradiation of the BPM-CdS/Pd shows its effectiveness in photocatalytic remediation of chemical contaminants. The CdS-Pd based bipolar membrane to carry out selective reduction and oxidation processes has also allowed us estimate the contribution of sacrificial donor oxidation in H2 production in water photoelectrolysis. The design and photocatalytic properties of this photocatalytic membrane will be discussed.
(Invited) Revisiting Functions of Gold Nanoparticles in Photocatalysis
Authors: Wu Nianqiang
Published: July 2022

This presentation revisits the functions of gold nanoparticles in photocatalysis. In photocatalyst, gold nanoparticles not only induce surface plasmon resonance but also have other functions. This talk will discuss how to separate different functions of gold nanoparticles in photocatalysis.
Large-Scale Synthesis of Photocatalytic TiO2 Nanotube Layers
Authors: Sopha Hanna , Baudys Michal , Krysa Josef , Macak Jan M.
Published: July 2022

Self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest over the past 15 years motivated for their wide range of applications including (photo-) catalysis, hydrogen generation and biomedical uses [1,2]. The synthesis of the 1D TiO2 nanotube layers is carried out by a conventional electrochemical anodization of valve Ti metal sheets in various electrolytes.

By now, the synthesis of TiO2 nanotube layers with different nanotube dimensions (diameter, length) and the application of these nanotube layers is well established on the laboratory scale. However, for real applications outside the laboratory scale, such as photocatalysis [3], TiO2 nanotube layers of much larger size are necessary. To date, just a few efforts were carried out to scale up the size of the nanotube layers to more than a few cm2 [3-7] due to the difficulty of controlling the parameters of the anodization process on a larger scale. The main challenge is the huge current received during the anodization of large substrates. This, in turn, leads to an increase in the electrolyte temperature that may result in dielectric breakdown of the growing nanotube layers.

In this presentation, the preparation of TiO2 nanotube layers on larger area titanium substrates (dozens of cm2) will be discussed, taking into account the control of the anodization parameters. The TiO2 nanotube layers with different thicknesses and nanotube diameters were employed for gas phase photocatalysis, following the ISO standards [3,8]. Experimental details and photocatalytic results will be presented and discussed.

References

[1] J.M. Macak, H. Tsuchiya, A. Ghicov, K. Yasuda, R. Hahn, S. Bauer, P. Schmuki, Curr. Opin. Solid State Mater., 11 (2007) 3.

[2] K. Lee, A. Mazare, P. Schmuki, Chem. Rev., 114 (2014) 9385.

[3] H. Sopha, M. Baudys, M. Krbal, R. Zazpe, J. Prikryl, J. Krysa, J.M. Macak, Electrochem. Commun., 97 (2018) 91.

[4] S. Franz, D. Perego, O. Marchese, M. Bestetti, J. Water Chem. Tech., 37 (2015) 108.

[5] H.-I. Kim, D. Kim, W. Kim, Y.-C. Ha, S.-J. Sim, S. Kim, W. Choi, Appl. Catal. A: Gen., 521 (2016) 174.

[6] J.P. Ghosh, G. Achari, C.H. Langford, Water Environ. Res., 88 (2016) 785.

[7] C. Xiang, L. Sun, Y. Wang, G. Wang, X. Zhao, S. Zhang, J. Phys. Chem. C 121 (2017) 15448.

[8] H.Sopha, M. Baudys, J. Krýsa, J. M. Macak, Ms in preparation.
Intrinsic Cu Nanoparticle Decoration of TiO2 Nanotubes: A Platform for Efficient Noble Metal Free Photocatalytic H2 Production
Authors: Hejazi Sina , Mohajernia Shiva , Kilian Manuela
Published: July 2022

The use of titanium dioxide (TiO2) for photocatalytic applications has been intensively investigated for years due to appropriate electronic properties, chemical and photocorrosion resistance, as well as the low cost of the material [1]. Although TiO2 has a suitable conduction band position for the photocatalytic H2 formation reaction, the hydrogen evolution reaction from water on a TiO2 surface is kinetically hampered. To tackle this problem, typically decoration with noble metals such as Pt, Pd, Au that act as a co-catalyst is employed. However, these noble metals are costly and a variety of pathways for replacing these elements have been explored. One of the promising substitutes for noble metals are copper and copper-compounds. The fabrication of copper co-catalyst loaded TiO2 nanotubes is conventionally carried out by chemical methods such as hydrothermal, impregnation, photo-deposition and electrochemical deposition [2]. However, a most straightforward and unique method to modify anodic TiO2 nanotube properties is employing, instead of pure Ti metallic substrate, a Ti‐X alloy in the anodization process, were X is another metal. During anodizing the second metal can be simultaneously oxidized and doped into the TiO2 lattice (in substitutional or interstitial position), giving the nanotubes a specific functionality [3–5]. A number of such intrinsically doped nanotube arrays have been reported, namely using Nb, Ta, Ru and etc., alloyed in Ti [3–5].

In this work, we grow intrinsically Cu doped TiO2 nanotubes (TiNTs) by self-organizing anodization of Ti-Cu binary alloys. We demonstrate that up to a copper concentration of 1.5 at.% in the alloy, self-ordered Cu2+-doped nanotubes can be grown. Under UV illumination the Cu2+ ion-doped oxide structures can be converted to nanotubes that carry metallic nanoparticles (NPs) uniformly decorated TiNTs. We investigate the formation of these metallic nanoparticles under UV illumination by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). The resulting intrinsic copper doped and decorated TiNTs provide a strongly enhanced photocatalytic activity for H2 evolution in comparison to pristine TiNTs. Key is the light induced conversion of the intrinsic Cu doping to metallic copper nanoparticles that act as a stable co-catalyst for H2 generation.

[1] K. Lee, A. Mazare, P. Schmuki, Chem. Rev.
2014, 114, 9385–9454.

[2] M. Janczarek, E. Kowalska, Catalysts.
2017,
7, 317-324.

[3] P. Roy, C. Das, K. Lee, R. Hahn, T. Ruff, M. Moll, P. Schmuki, J. Am. Chem. Soc.
2011,
133, 5629–5631.

[4] M. Altomare, K. Lee, M.S. Killian, E. Selli, P. Schmuki, Chem. - A Eur. J.
2013, 19, 5841–5844.

[5] C. Das, P. Roy, M. Yang, H. Jha, P. Schmuki, Nanoscale. 2011, 3, 3094–3096.

Figure 1
(Invited, Digital Presentation) Photo-Electrochemical Water and CO2 Reduction Devices Operating Under Concentrated Radiation
Authors: Haussener Sophia , Patel Mahendra , Boutin Etienne
Published: July 2022

Achieving high current densities while maintaining a high energy conversion efficiency is one of the main challenges for enhancing the economic competitiveness of solar fuel producing photo-electrochemical devices [1]. I will discuss two device implementations utilizing concentrated irradiation to achieve high current density operation. The water-splitting device is utilizing thermal integration to sustain high performance while dealing with high current density and the corresponding overpotentials [2]. I will quantify the theoretical increase in the maximum efficiencies at given current densities of photoelectrochemical devices resulting from thermal synergies. I will then discuss device implementation of such an approach and show how more realistic device models (multi-dimensional, multi-scale, multi-physics) can be used to support the device implementation and its operational understanding [3]. I will then show how the design principles developed for water splitting can be translated to CO2 reduction devices and discuss a corresponding device implementation.

[1] M. Dumortier, S. Tembhurne, S. Haussener, Energy Environmental Science, 8: 3614-3628, 2015.

[2] S. Tembhurne, F. Nandjou, S. Haussener, Nature Energy, 4: 399-407, 2019.

[3] S. Tembhurne, S. Haussener, Journal of The Electrochemical Society, 163: H1008-H1018, 2016.
Capping-Ligand Density on Cu Nanoparticles Determining Multi-Carbon Product Selectivity in Electrochemical CO2 Reduction
Authors: Oh Yusik , Byon Hye Ryung
Published: July 2022

Carbon dioxide (CO2) emission from the combustion of fossil fuel causes global warming and climate change. Much attention has been paid for recycling of CO2 gas, namely converting this greenhouse gas to high-value fuels such as multi-carbon products (ethylene, ethanol, propanol, etc.). In particular, electrochemical CO2 reduction reaction (CO2RR) is one of the promising methods operated at ambient pressure and room temperature. By using gold and silver catalysts, carbon monoxide (CO) is successfully yielded with >80% Faradaic efficiency. In contrast, it is still challenging to produce multi-carbon (i.e., C2+) products. Copper (Cu) is known as the sole catalyst to yield C2+ products by affording the suitable binding energy to the intermediate of *CO (the asterisk denotes the surface adsorption). Although various synthetic methods for the preparation of Cu nanoparticles (NPs) have been developed to increase the surface area and design of the preferred facets for the CO2 reduction, the highly sensitive Cu surface in air and from contaminants resulted in variable Faradaic efficiencies for C2+ production. In particular, the capping ligands, which coat the Cu surface to stabilize the designed nanostructures, should significantly influence the catalytic efficiency and stability. However, their effects have been little studied.

Here, we show the enhanced catalytic activity and stability of Cu NPs for the C2+ yield by eliminating the capping ligands.[1] The pristine Cu NPs with ~8 nm of diameter were prepared by using a capping ligand of tetradecylphosphonate (TDP). After UV-ozone treatment, the TDP ligands were eliminated in part; The phosphorous signal was attenuated, and the Cu surface was oxidized in X-ray photoelectron spectra. In addition, the carbonyl oxygen (O=C) emerged from the damaged TDP. In contrast, the carbon substrate and the surface roughness of the Cu were insignificantly changed. These UV-ozone-treated Cu NPs showed ~50% Faradaic efficiency of the C2+ conversion (FEC2+) at –0.98 V vs. RHE, which was twice as high as that of the pristine Cu NPs (~25%). In particular, the FEC2+ gradually increased as the remaining capping ligands were removed, indicating the increased catalytic sites for 3 h CO2RR. In sharp contrast, the FEC2+ from the pristine Cu NPs was consistently low despite the partial stripping of the capping ligands, suggesting the negligible formation of the C2+ active sites. For prolonged chronoamperometry tests for 20 h, these FEC2+ values were retained for both catalysts, while the size and shape of Cu catalysts were differently changed. The UV-ozone-treated ones proceeded little agglomeration and contained many grain boundaries. In contrast, the pristine Cu NPs were transformed to the cubic particles with ~100 nm size. The distinct alternations of Cu structures are closely related to the yield of the C2+ active sites, which I will discuss in this presentation.

[1] J. Mater. Chem. A, 9, 11210 (2021)

Figure 1
(Invited, Digital Presentation) Sub-Nanoscale Electrocatalyst Design for Enhanced CO2 Conversion
Authors: Kwon Youngkook
Published: July 2022

The majority of today’s research in electrochemical catalysis is centered in designing catalyst materials and processes that can surpass the current benchmarks of the classical catalysis. However, developments of the performance parameters of the important electrochemical reaction such as CO2 reduction reaction has been sluggish due to the intrinsic limitations such as adsorption energy scaling relations of the intermediate species.1 Recently, theoretical and experimental studies have revealed that the electrochemical reactions confined within a very small space with a wall separation under 1 nanometer outperforms the reactions without confinement.2-4 Theoretical models suggested that the enhancement from the nanoscopic confinement arises from the electronic interaction of the adsorbed species with multiple surfaces, which breaks the adsorption energy scaling relations of the important intermediate species.2

As a proof-of-concept, we synthesized novel copper oxide (CuOx) nanoparticles (NP) and tin oxide (SnOx) NP with highly controlled sub-nanoscale interplanar gaps of widths <1 nm via the lithium electrochemical tuning method. Transmission electron microscopy (TEM) and 3D tomo-scanning TEM (STEM) analysis confirm the presence of a distinct segmentation pattern and the newly engineered interparticle confined space in the designed catalysts. Atomic-gap controlled to 5-6 Å CuOx allows a current density exceeding that of unmodified CuOx nanoparticles by about 12 folds and a Faradaic efficiency of ≈80% to C2+.3 Separately, lithiated SnOx exhibits a significant increase in CO2RR vs. hydrogen evolution selectivity by a factor of ~5 with 20% higher formate selectivity relative to pristine SnO2 NPs at −1.2 VRHE.4 Density functional theory calculations indicate that the enhanced performance is attributable to a gap-stabilization of the rate-limiting *COOH and/or *OCHO intermediates. These results highlight the potential of controlled atomic spaces in directing electrochemical reaction selectivity and the design of highly optimized catalytic materials.

Keywords

: Electrocatalyst, CO2 reduction, Space Confinement, Sub-Nano Spacing

Kwon et al., ACS Energy Lett., 2020, 5, 2987-2994.

Lu and Cheng et al., J. Phys. Chem. Lett., 2020, 11, 1896-1902.

Kwon et al., Adv. Energy Mater., 2020, 19034423.

Kwon et al., Adv. Funct. Mater., 2021, 2107349.
(Digital Presentation) Electrochemical-Mechanical Coupling between Single-Ion Conducting Electrolytes and Metal Electrodes
Authors: Carmona Eric A , Song Yueming , Albertus Paul
Published: July 2022

Solid-state metal batteries provide increased gravimetric and volumetric energy density compared to conventional Li-ion batteries and their development is essential for meeting performance and cost targets for consumer applications. Conventional liquid electrolytes exhibit reactivity with pure Li and undergo significant dendrite formation, thus single-ion conducting solid electrolytes have been explored to prevent and mitigate dendrite formation as they possess high modulus, high room temperature ionic conductivity, and the potential to improve safety compared to organic liquid electrolytes. Unfortunately, ceramic single-ion conducting electrolytes such as LLZO have been demonstrated to form dendrites above critical current densities. Understanding the electrochemical-mechanical coupling between the electrolyte and electrode can help elucidate the mechanisms of dendrite formation and propagation in solid-state metal batteries as well as methods for prevention and mitigation. Mechanical stresses arise during battery operation due to external stack pressure, expansion and contraction of intercalation electrodes, and the deposition and stripping of metal electrodes. As we demonstrated in a previous work1, the thermodynamic state of the electrode is affected by its mechanical state, therefore, applied stresses alter the equilibrium potential of metal electrodes. Additionally, the mechanical state of the electrode can influence the metal electrode plating and stripping kinetics. Previous studies in the literature have examined the effect of mechanics on the current distribution; however, careful attention is required when coupling electrochemistry and mechanics as well as consideration as to the importance of the mechanical state of the electrolyte. This talk will focus on the effects of mechanical stresses on the current distribution at the metal electrode/single-ion conducting electrolyte interface and the implications on dendrite formation and mitigation.

References:

(1) Carmona, E. A.; Wang, M. J.; Song, Y.; Sakamoto, J.; Albertus, P. The Effect of Mechanical State on the Equilibrium Potential of Alkali Metal/Ceramic Single-Ion Conductor Systems. Advanced Energy Materials
2021, 11 (29), 2101355. https://doi.org/10.1002/AENM.202101355.
Investigation of the Hydrogen Mass Fraction Distribution in a Polymer Electrolyte Fuel Cell through Experimentally Validated Simulation
Authors: Bodner Merit , Penga Željko , Hacker Viktor
Published: July 2022

During the start-up of a fuel cell, but also during transient operation, the availability of hydrogen at any location of the active surface of the fuel cell anode is crucial for its safe and reliable operation. When neglecting water vapor, inlet hydrogen mass fractions below one may occur when inert gases or air are flushed out during start-up or as a result of nitrogen accumulation due to fuel recirculation in fuel-efficiency driven system operation [1], [2]. Therefore, in a combined experimental and simulation-based approach, the hydrogen mass fraction distribution over the active area of a 25 cm2 single cell was investigated and the impact of it on known degradation mechanisms such as the corrosion of carbon-based anode catalyst support was determined through off-gas analysis. With a new approach to time-resolved computational fluid dynamic simulation (based on an existing model by Penga et al. [3]) the progression of local conditions during current ramp up were visualized [4].

References

[1] B. Wang, H. Deng, and K. Jiao, “Purge strategy optimization of proton exchange membrane fuel cell with anode recirculation,” Appl. Energy, vol. 225, no. May, pp. 1–13, 2018, doi: 10.1016/j.apenergy.2018.04.058.

[2] K. Kocher, S. Kolar, W. Ladreiter, and V. Hacker, “Cold start behavior and freeze characteristics of a polymer electrolyte membrane fuel cell,” Fuel Cells, vol. 21, no. 4, pp. 363–372, 2021, doi: 10.1002/fuce.202000106.

[3] Ž. Penga, C. Bergbreiter, F. Barbir, and J. Scholta, “Numerical and experimental analysis of liquid water distribution in PEM fuel cells,” Energy Convers. Manag., vol. 189, pp. 167–183, Jun. 2019, doi: 10.1016/j.enconman.2019.03.082.

[4] M. Bodner, Ž. Penga, W. Ladreiter, M. Heidinger, and V. Hacker, “Simulation-Assisted Determination of the Start-Up Time of a Polymer Electrolyte Fuel Cell,” Energies, vol. 14, no. 23, p. 7929, Nov. 2021, doi: 10.3390/en14237929.
(Invited, Digital Presentation) Infiltrated Electrodes for High Temperature Energy Conversion, Electrolysis, and Chemical Synthesis
Authors: Tucker Mike C , Hu Boxun , Welander Martha M , Shen Fengyu , Lau Grace Y.
Published: July 2022

Solid oxide cell (SOC) infiltrated electrodes typically consist of a ceramic or cermet porous scaffold with the pore walls coated with catalyst particles. The pore size of the scaffold is 1 to 50 mm, whereas the catalyst particles are 10 to 300 nm. This scaffold provides a stable and durable mechanical structure, and the fine catalyst particles provide high surface area for electrochemical and heterogeneous reactions. The scaffold is sintered and bonded to the other layers of the complete cell. After this high temperature processing is finished, catalyst precursor solution is flooded into the scaffold and fired at moderate temperature to form the desired catalyst composition and phase. Because the scaffold is sintered in the absence of catalysts, re-optimization of the fabrication process, ink formulation, deposition process, and sintering protocol is not needed when a new catalyst is introduced to the cell design. Instead, a new precursor solution can be prepared from a stoichiometric mixture of metal salts, with minimal change in processing. This approach makes it straightforward to screen many catalyst compositions in a short period of time, and adapt an existing cell structure for a wide variety of applications.

The Lawrence Berkeley National Laboratory metal-supported solid oxide cell (MS-SOC) design has a thin electrode scaffold of zirconia ceramic co-sintered on a thick porous stainless steel support layer. Both layers are coated with infiltrated catalysts. The catalyst precursor solution is an aqueous mixture of metal nitrate salts. After the solution is flooded into the pores of the scaffold, it is dried and heated in air to convert the nitrate salts to mixed metal oxides. The oxides can then be reduced to metals by firing in reducing atmosphere, if desired. The drying rate, heating rate, conversion temperature, and other processing parameters can have a dramatic impact on the catalyst particle morphology and ultimately on the performance and durability of the electrochemical device.

Depending on the choice of catalyst composition, the MS-SOCs can be configured as fuel cells, electrolysis cells, or chemical conversion reactors. Several examples will be highlighted, including: fuel cell operation with hydrogen, ethanol, and natural gas; steam electrolysis for hydrogen production; and oxidative coupling of methane for valuable chemical synthesis. In each case, technical progress will be presented with a focus on catalyst development and device performance.

Figure 1
Modeling Solid Oxide Fuel Cells for Hybrid-Electric Turbo Generators in Aircraft Applications
Authors: Ashar Akhil , Braun Rob J , Jackson Greg
Published: July 2022

Air travel accounts for a significant portion of domestic and global greenhouse gas emissions. Decarbonized electric propulsion has the potential to be disruptive to replace conventional gas turbine based engines and could be an attractive solution to reduce aircraft emissions. This work aims to design a pressurized hybrid solid oxide fuel cell/gas turbine turbo generator using carbon neutral liquid fuels for narrow body commercial aircraft with high gravimetric power densities. Novel Ni/GDC based cell architectures are used to lower cell operating temperature and thereby, reduce both stack costs (e.g., interconnects and seals) and system balance-of-plant costs. There is currently limited understanding of the operating characteristics and optimum conditions for employing GDC based cells in these applications. Further, the mixed ion electronic conducting (MIEC) nature of GDC and its impact on cell voltage and electrochemical performance has yet to be quantified. This work presents a one-dimensional, down-the-channel stack model that captures physicochemical processes for an intermediate temperature Ni/GDC based fuel cell. The leakage current phenomena of MIEC anodes is captured by calculating open circuit voltage as a function of conductivity, temperature and pressure. Activation overpotentials are calculated based on published results in literature that fit exchange current densities and charge transfer coefficients based on experimental electrochemical impedance spectroscopy measurements [1,2]. Fickian diffusion for mass transport across the porous electrodes and rate mechanisms to evaluate reforming characteristics are used. The model predicts electrochemical performance for varying cell temperatures and flow rates. The distribution of overpotentials with cell temperature and current density is analyzed. Thermal management of power dense stack operating conditions is critical to understand. Thus, the stack model is also employed to within a subsystem where it is integrated with an autothermal reformer and anode gas recycle to parametrically assess operating conditions and performance, particularly towards minimizing cooling air flow requirements.

Figure 1
Heterostructured Functional Materials through Molten Salt Synthesis for Solid Oxide Fuel Cells and Electrolysis Cells
Authors: Gopalan Srikanth , Levitas Benjamin
Published: July 2022

La0.6Sr0.4Co0.2Fe0.8O3 (LSCF)−La0.8Sr0.2MnO3 (LSM) heterostructure crystalline materials have been synthesized in a simple, one-step via reaction-deposition process using a molten salt. Two-phase perovskite composites can be synthesized in times as short as 10 minutes in a molten salt solvent. X-ray diffraction and S/TEM energy dispersive X-ray spectroscopy have been utilized to confirm the formation of an LSM shell on LSCF cores in all samples when adjusting dwell time, core size, weight ratio between core and shell precursors, and weight ratio of powder to salt. Specifically, decreasing the LSCF core size increases core−shell yield. Smaller cores result in a greater density of facets on the crystal surface and provide more favorable sites for LSM heterogeneous nucleation. By decreasing the weight ratio of shell precursor to core decreases shell thickness, and reduces the number of homogeneously nucleated LSM nanoparticles, and thereby increases core−shell yield. Increasing the amount of molten salt solvent relative to precursors decreases supersaturation in the melt and results in less uniform, and isolated shell deposition on the cores. The synthesized heterostructred nanoparticles have been functionalized into electrodes for solid oxide fuel cells and electrolysis cells. Symmetrical cells fabricated from baseline LSCF electrodes are compared with symmetrical cells fabricated from the molten salt-synthesized heterostructred electrodes. The heterostructured electrodes are shown to have significantly lower polarization resistance compared to baseline LSCF electrodes, showing the promise of the molten salt process to achieve heterostructured electrodes with substantially reduced polarization resistance.
(Keynote) Making and Breaking Bipolar Membrane Protonic Diodes
Authors: Schulte Leanna , Phun Gabriel S. , McClarin Geoffrey R. , Heffernan Ethan J. , White William , Renna Lawrence A. , Ardo Shane
Published: July 2022

Bipolar membranes have been studied for >50 years for application in electrodialysis at moderate current densities (<100 mA/cm2). In the past decade bipolar membranes have experienced a renaissance due to interest in driving higher current density processes with intentional pH gradients between the anode and cathode, such as CO2/H2O electrolysis and electrochemical generation of acid and base for direct oceanic carbon capture, two applications that my group actively studies. My group’s main contribution to this field is that we recently showed that bipolar membranes are in fact high-quality protonic diodes, where water serves as a (protonic) semiconductor. Using Mott–Schottky analysis and Butler–Volmer analysis, we reported on the performance of said materials. Using this platform, we have demonstrated photovoltaic action from photoacid-dye-sensitized bipolar membranes. More recently, we have studied how intentional placement of proton-donating and proton-accepting groups in the space–charge region forms a recombination/generation junction, which are the non-tunneling variants of tunnel junctions that are important in tandem solar cells. This allows for rapid protonic conduction across originally rather insulating junctions, as desired for ionic conductors in most electrochemical devices. Collectively, our efforts form the foundational framework for new functions and resulting applications that benefit from protonic transfer and transport.
(Invited) Regulating Electronic Structure for Clean Energy Powered Water Electrolysis on Non-Precious Catalysts
Authors: Li Jiangtian , Chu Deryn , Baker David R. , Jiang Rongzhong
Published: July 2022

The need for clean energy, predominantly wind and sun, to replace fossil fuels is in high demand for the carbon neutrality. The intermittent nature of the renewable energy sources is one of the most important challenges. A potential solution is to store the extra electricity in the form of chemical fuels, and then reconvert on demand. Electrochemical water splitting to produce hydrogen and oxygen is an appealing and sustainable approach. The benchmark electrocatalysts for water electrolysis are noble metal Pt- and Ir/Ru-based materials. Nevertheless, the scarcity and the high cost of these precious catalysts severely hinder their widespread applications. Developing non-precious electrocatalysts has been one long-term target, but still remains a great challenge. In this presentation we will show our research efforts and design strategies by regulating the electronic structures on transition metal-based electrocatalysts for hydrogen evolution, oxygen evolution as well as constructing the water electrolyzer powered by solar energy.
Impacts of Manifold Geometry and Flow Configuration on Shunt Current, Current Distributions, and Crossover in an Alkaline Electrolysis Stack
Authors: Lopata Joseph Steven , Kang Sanggyu , Cho Hyun-Seok , Kim Chang-Hee , Shimpalee Sirivatch
Published: July 2022

Alkaline diaphragm water electrolysis (ADWE) devices have undergone widespread commercialization for about a century to date. Their high resistance relative to polymer electrolyte cells has motivated the employment of ion exchange membranes. However, recent advancements in the zero-gap configuration, in which porous electrodes are in contact with the porous ZrO2/polysulfone diaphragm, hold promise in extending the use of this inexpensive and durable technology by eliminating a portion of resistive losses.

Desired improvements to the technology include reductions in electrode void fraction, crossover, and shunt current. Lower void fractions increase current density by allowing aqueous ions to both migrate and react at a greater portion of the electrode surface. The geometry investigated utilizes a design in which electrolyte feed is injected from the manifolds directly into the porous electrode without an intermediary flow field, which promotes product gas expulsion 1. Crossover is of particular concern because it puts a lower constraint on the practical thickness of the porous separator. Different modes of operation are investigated in this work to understand what provokes gas crossover locally, as previously done 1. Shunt current arises whenever an electrolyte solution is fed to a stack containing multiple electrodes contacted in series, inducing potential gradients in the electrolyte and leading to ion migration. This can lead to local potential gradients in the manifolds that allow undesired corrosion of the current collectors to occur.

This three-dimensional (3-D) computational fluid dynamics model of an ADWE stack of five cells in series aims to gather details of the aforementioned problems, notably how they vary in 3-D space. Void fractions and crossover are compared between simulations of co- and counter-current operation. The locations of potential gradients that threaten the lifespan of the system are identified, and this information is used to suggest strategies to reduce or mitigate high void fraction, high local crossover, and high potential gradients in manifolds. Additionally, as this is a stack model, through-plane current distributions and notes on the fluid flow rates from cell to cell are provided.

References

J. S. Lopata, S-G. Kang, H-S. Cho, C-H. Kim, J. W. Weidner, S. Shimpalee, Electrochim. Acta, 390, 138802 (2021).

Figure 1
(Invited) Catalyst Layers for Fluorine-Free Hydrocarbon PEMFCs
Authors: Holdcroft Steven , Balogun Emmanuel , Mardle Peter , Breitwieser Matthias , Hguyen Hien
Published: July 2022

Electrochemical energy conversion devices such as fuel cells are crucial for the development of renewable, sustainable alternative energy vectors. The implementation of fuel cell technology is of particular interest in portable, transportation, and stationary energy conversion sectors. There are challenges that still impede fuel cell commercialization at scale: cost, performance, and durability of the membrane-electrode-assemblies (MEA)s that comprise fuel cell stacks. MEAs typically consist of catalyst layers (CL) coated on either side of a proton-exchange membrane (PEM), and gas diffusion layers (GDL) which control water management and reactant gas mass transport. The CL provides a path for proton, electron, and gas transport to (and from) the Pt catalyst surface. Commonly, a perfluorosulfonic acid (PFSA) ionomer, e.g., Nafion® is employed as both the proton exchange membrane (PEM) and ionomer. However, perfluorinated materials are not without challenges as their manufacture utilizes controlled substances and potentially environmentally hazardous chemical feedstocks, which add to their relatively high cost. In contrast, fluorine-free hydrocarbon-based analogues may be prepared from ubiquitous, readily available chemical feedstocks, and afford much-reduced gas permeability. In this presentation, highly performing (power densities of >1 W cm-2), sulfo-phenylated poly(phenylene)PPB-H+ solid polymer electrolyte will be reported as a complete substitute for incumbent PFSA materials in PEMFCs, serving both as the electrode catalyst binder, and membrane.
(Invited) Novel Nature-Inspired Concepts to Design Ionomeric Nanomaterials for Energy Conversion and Storage Devices
Authors: Dishari Shudipto K
Published: July 2022

Ion-conducting polymers (ionomers) are an integral part of renewable energy-driven technologies. Proton exchange membrane fuel cells (PEMFCs) have already been incorporated into low-duty vehicles and are now being adopted in heavy-duty vehicles. Therefore, we need more durable and efficient fuel cell materials than ever. A major technical challenge of PEMFCs is the ion transport limitation at the ionomer-catalyst interface which negatively impacts the efficiency of the cells. The current state-of-the-art fuel cell ionomers (both fluorocarbon- and hydrocarbon-based) conduct protons efficiently in bulk, several tens of micron thick, free-standing membranes, but poorly in sub-micron thick films. This needs attention as sub-micron thick ionomer layers are used as catalyst binders on electrodes of PEMFCs and other energy conversion and storage devices. However, the nanoscale behavior of these existing ionomers within complex hydration environment is not well-understood yet. More importantly, ionomers are rarely designed to improve the thin film ion conduction properties. To address and overcome these issues, we do not only design innovative nanoscale materials characterization techniques to explore the distribution of ion conduction environment across ionomer films/membrane, but also design novel classes of ionomers inspired by natural living systems to facilitate ion conduction in thin films. We experimentally measure the ion conductivity, morphology, and mechanical properties, and combine them with computational studies to elevate our understanding of ion conduction mechanism within 10-200 nm thick films of these newly designed ionomers. The results suggest the great promise of these new classes of ionomers as efficiently ion-transporting catalyst binders for fuel cells, electrolyzers, and batteries.
(Invited, Digital Presentation) Polybenzimidazole and Its Use in Energy Storage and Conversion
Authors: Henkensmeier Dirk
Published: July 2022

Polybenzimidazole (PBI) is a unique polymer. It has high mechanical strength and stability, and is not conductive. However, in contact with acids, the imidazole rings are protonated, and PBI becomes proton conductive. In contact with alkaline solutions, the amine groups are deprotonated, and PBI becomes hydroxide conductive. Control of the doping process allows to adjust the uptake and hence allows to control conductivity and permeability of PBI membranes. Therefore, PBI can be used in various ways for several applications.

Phosphoric acid doped PBI blends were tested in the HT PEMFC, and showed more than >2000 hours stable, high performance operation at very challenging high current density of 800 mA/cm2 (one of world-best results).[1]

Sulfuric acid doped PBI membranes were developed for use in the vanadium redox flow battery. We show that stable performances with an energy efficiency >91% and coulomb efficiency >99% @ 80 mA/cm2 can be achieved, which is one of the highest reported performances.[2, 3]

By using a newly developed membrane fabrication process, hydroxide conducting membranes with a conductivity of > 310 mS/cm2 were be obtained. Porous supports enhanced the mechanical stability of these membranes, and PEM-water electrolyser-like performance was achieved in an alkaline water electrolyser, which was successfully operated for 1000 hours without failure.[4]

A common way to increase the mechanical stability of membranes is reinforcement with a porous support. The drawback is that different swelling ratios of matrix and support can form voids, which results in unacceptably high gas crossover in electrolyzers and fuel cells. To tackle this issue, we pore filled an electrospun PBI fiber mat with a bomoalkylated polymer and reacted it with the imidazole groups available on the PBI fiber surface, thus forming a covalently bonded interface. In a final step, the remaining bromoalkyl groups were quaternized. The membrane was tested for 200 hours in an electrolyzer, and showed no signs of degradation. [5]

[1] N. Nambi Krishnan, N.M.H. Duong, A. Konovalova, J.H. Jang, H.S. Park, H.J. Kim, A. Roznowska, A. Michalak, D. Henkensmeier, Polybenzimidazole / tetrazole-modified poly(arylene ether) blend membranes for high temperature proton exchange membrane fuel cells, J. Membr. Sci., 2020, 614, 118494. https://doi.org/10.1016/j.memsci.2020.118494

[2] C. Noh, D. Serhiichuk, M. Najibah, Y. Kwon, D. Henkensmeier, Optimizing the performance of meta-polybenzimidazole membranes in vanadium redox flow batteries by adding an alkaline pre-swelling step, Chem. Eng, J., 405 (2021) 126574. https://doi.org/10.1016/j.cej.2020.126574

[3] unpublished results

[4] under review

[5] Malikah Najibah, E. Tsoy, H. Khalid, Y. Chen, Q. Li, C. Bae, J. Hnát, M. Plevová, K. Bouzek, J.H. Jang, H.S. Park, Dirk Henkensmeier, PBI nanofiber mat-reinforced anion exchange membranes with covalently linked interfaces for use in water electrolysers, J. Membr. Sci., 2021, 640, 119832. https://doi.org/10.1016/j.memsci.2021.119832
Comparison of Different Optimization Methods for the Microstructure of Proton Exchange Membrane Fuel Cells
Authors: Lamb James , Andrei Petru
Published: July 2022

Proton exchange membrane fuel cells (PEMFCs) have attracted much attention in the research and commercial sectors because they are environmental friendly and have relatively high power density compared to most other energy storage devices based on electrochemical processes. A significant part of the research on PEMFCs is related to decreasing the cost and improving the structure of PEMFCs by optimizing numerically the microstructure of these devices including the non-uniform porosity, carbon, nafion, and catalyst (i.e. platinum) distributions and the geometrical characteristics. The existing optimization techniques can generally be divided into heuristic and non-heuristic techniques. Heuristic techniques usually use stochastic approaches that search the optimization space using trial-and-error methods. Examples of such techniques include the genetic algorithm, particle swarm optimization, differential evolution, simulating annealing, harmony search, memetic algorithms, etc. These techniques can be applied to optimize a small number of design variables and often need to be used with simplified (often purely mathematic and not based on fundamental physics) models, such as compact, reduced-order models, or equivalent circuit models. On the other hand, non-heuristic techniques are deterministic and often require evaluating the gradient of the objective function. In general, these techniques have local convergence and their rate of convergence can be increased, using second-order derivatives such as the Hessian matrix, or taking advantage of the particular functional form of the objective function. Non-heuristic techniques usually require between a few tens of iterations to optimize the objective function compared to heuristic techniques which require at least tens of thousands of iterations.

In this presentation we will make a thorough critical review of the different optimization methods used in the literature for PEMFCs. In additional, we will present the results of our efforts to develop a full-cell optimization algorithm for PEMFCs using the adjoint method [1-3]. The advantages and disadvantages of different methods, including the adjoint method, will be discussed in detail and examples of sample simulations results will be presented.

References

1. Lamb and P. Andrei, “Optimization of 2-D Spatial Distributions of Pore Sizes, Platinum Content, and Nafion Amount in PEMFC”, ECS Meeting Abstracts, (2021).

Lamb and P. Andrei, ECS Transactions, 98, 67 (2020).

Lamb, G. Mixon and P. Andrei, J. Electrochem. Soc, 164, E3232 (2017).