bluuebunny/crossref_metadata_2025 huggingface dataset:
Groovy Electrodes Enable Facile O2 and H+ Transport in PEMFCs
Authors: Lee ChungHyuk , Komini Babu Siddharth , Mukundan Rangachary , Borup Rod L. , Spendelow Jacob S.
Published: July 2022

Polymer electrolyte membrane fuel cells (PEMFCs) are promising alternative to internal combustion engines, owing to their capability to produce on-demand power with zero local carbon emissions. However, PEMFCs suffer from limitations related to performance, particularly for heavy-duty vehicle applications [1]. A major contributor to the performance loss is the cathode electrode; uncontrolled conventional electrode structures lead to non-ideal transport pathways of O2 and H+ [2], subsequently leading to performance loss. Here, we report an alternative electrode structure termed groovy electrodes, fabricated via patterned Si templates. Si templates with desired patterns are fabricated through photolithography and deep-reactive ion etching techniques (Fig. 1a), and an electrode layer is coated onto the template and subsequently transferred to the membrane or the gas diffusion layer. The resulting electrode features ordered grooves with consistent depth and width (Fig. 1b-c). We will present how this alternative structure enables improved H+ transport (enabled by higher ionomer content) with grooves facilitating effective O2 transport to reaction sites. We will also demonstrate the benefits of a groovy electrode for the durability of PEMFCs.

Reference

Cullen et al., Nat. Energy, 6, 462 (2021).

Ramaswamy et al., J. Electrochem. Soc., 167, 064515 (2020).

Figure 1
Understanding Key Factors during Dod Inkjet Printing Towards Precise Fabrication of Micro Energy Systems
Authors: Huang Hong , Hill Theresa
Published: July 2022

There is an ever-increasing need for micro energy systems that can power miniature, unmanned, or remotely-located devices. Drop-on-Demand (DOD) inkjet fabrication is uniquely positioned for this demand due to its low-cost processing with microscale resolution, high throughput, reproducibility, and ease in shape design. This study seeks to capitalize on the advantages of DOD inkjet printing for application to manufacturing micro energy conversion/storage systems, by defining the fundamental jet kinematics and key factors underpinning the inkjet printing process.

The ink used in this study was a dilute colloidal ink suspension composed of a common solid oxide fuel cell (SOFC) cathode material [La0.6Sr0.4Fe0.8Co0.2O3 (LSFC)] and organic solvent α-terpineol. The results were evaluated systematically in terms os final deposition quality, resolution, and microstructure. Favorable fluid kinematics were identified that attained uniform, well-shaped, circular 0-D dots about 0.1 µm thick and 60 µm in diameter. To increases the microfeature thickness and x/y plane dimensions , multiple and/or sequential ink passes were employed. For printing 1-D lines, the spacing between droplets was imperative to fabricating quality micro features. Using appropriate conditions, 1-D lines with x/y dimensions < 100 µm and controllable z axis dimensions at 0.1 µm per printing pass with dense, open or networked microstructures were demonstrated. 2-D planes at the dimensions as small as 100 µm by 100 µm were also achieved with smooth surface and continuous intra-planar ceramic coverage. In the course of post-processing the inkjetted cathodes, it was observed that the submicron cathode films printed at optimal conditions, after being sintered at controlled conditions, were uniform, smooth and free of cracks or delamination.

This research demonstrated through fundamental understanding and control of the inkjet fabrication process, cathode features can be printed with controlled dimension and quality towards producing a functioning micro SOFC operable at low temperatures. The knowledge gained from this research will be appliable to other micro energy conversion and storage systems.
Spatially Resolved Deconvolution of Loss Processes in PEM Fuel Cells
Authors: Oppek Philipp , Geörg Mischa , Goosmann Tobias , Reshetenko Tatyana V. , Weber Andre , Krewer Ulrike
Published: July 2022

The complex operating behaviour of PEM Fuel Cells is heavily influenced by different non-linear loss processes, which limit the cell performance. Depending on the operating conditions, the different losses change in magnitude and characteristic time constants [1]. During technical operation of large-sized PEM Fuel Cells, gradients in operating conditions occur along the gas channels, resulting in an inhomogeneous current density distribution. This is caused by the locally varying electrochemical activity due to in-plane gradients in concentrations of reactants and reaction products, gas pressure and temperature. Consequently, each loss process occurs locally distributed to a varying degree. Therefore, a profound knowledge about the spatial distribution of losses is essential for optimizing the operating strategy as well as the cell and stack components.

The commonly measured I/V characteristics provide only integral information about the overall performance. Thus, the data obtained represent merely the sum of all loss processes averaged over the entire cell area and do not allow detailed conclusions about the respective spatial distribution along the channel.

Inevitably, in order to deconvolute the loss processes in the entire area of large sized cells, an approach is required that provides deeper insight in the processes and their interdependencies. For this purpose, an impedance-based methodology is developed that enables a spatially resolved deconvolution of loss processes. It is based on electrochemical impedance spectroscopy (EIS) and an impedance data analysis by the distribution of relaxation times (DRT) [2,3] that is applied to a segmented cell [4] with almost gradient-free segments. By systematically varying operating conditions the different loss processes are identified, quantified and separated with respect to their characteristic frequencies.

In this contribution the design of the test bench and the segmented cell will be presented. Furthermore, first results regarding the electrochemical characterization and the impedance-based deconvolution of loss processes in a segmented cell will be discussed.

M. Heinzmann et al., J. Power Sources 402, pp. 24-33 (2018).

H. Schichlein et al., J. Appl. Electrochem. 32, pp. 875-882 (2002).

E. Ivers-Tiffée et al., J. Ceram. Soc. Japan 125, pp. 193-201 (2017).

T. Reshetenko et al., J. Electrochem. Soc. 163, pp. F1100-F1106 (2016)
Oxygen Reduction Reaction Catalyzed By Silicon and Nitrogen Co-Doped Carbon
Authors: Kruusenberg Ivar , Kaare Kätlin , Palgrave Robert , Tsujimoto Masahiko , Kuzmin Anton , Shainyan Bagrat
Published: July 2022

Finding an alternative catalysts for the oxygen reduction reaction (ORR) has been a key issue in modern

electrocatalysis. Traditional platinum-based catalysts are not viable in the long term and thus much effort

has been focused on non-precious metal catalysts. Heteroatom doped and metal-heteroatom co-doped

carbon materials have emerged as the main candidate for replacing the platinum-based catalysts.

Different MN4 macrocycles, such as metal phthalocyanines and porphyrins, have been studied as

promising materials to prepare electrocatalysts for ORR in alkaline media [1]. While the development of

non-precious metal and non-metal carbon catalysts has gained a lot of attention recently, non-metal

phthalocyanines are a less studied topic [2].

In this work a novel catalyst material including multi-walled carbon nanotubes (MWCNT) and silicon

phthalocyanine dichloride (SiPcCl2) was synthesized and the electrochemical activity towards the oxygen

reduction reaction (ORR) in alkaline media was studied. Different ratios of phthalocyanine-to-nanotubes

were pyrolyzed at 800 °C. After optimizing the ratio of phthalocyanine-to-nanotubes, the pyrolysis process

was also carried out at different temperatures, but the results showed that the best temperature for

pyrolysis is still 800 °C. ORR activity on SiPc/MWCNT catalyst was studied in 0.1 M KOH by employing

rotating disc electrode method. Physical characterization was carried out with X-ray photoelectron

spectroscopy and transmission electron microscopy. The results showed successful incorporation of

silicon and nitrogen into the carbon framework. We show that doping MWCNTs with a non-metal

phthalocyanine creates a highly active ORR catalyst rivaling the activity of metal-based catalysts in

alkaline conditions. This work clearly demonstrates that non-metal macrocyclic compound modified

carbons, similar to the the SiPc/MWCNT can be used as alternative cathode catalysts for the metal-air

batteries and alkaline membrane fuel cells.

[1] Y. Liu, X. Yue, K. Li, J. Qiao, D.P. Wilkinson, J. Zhang, PEM fuel cell electrocatalysts based on

transition metal macrocyclic compounds, Coord Chem Rev. 315 (2016) 153-177.

[2] K.-K. Türk, K. Kaare, I. Kruusenberg, M. Merisalu, U. Joost, L. Matisen, V. Sammelselg, J.H. Zagal, K.

Tammeveski, Oxygen electroreduction on zinc and dilithium phthalocyanine modified multiwalled carbon

nanotubes in alkaline media, J. Electrochem. Soc. 164 (2017) H338-H344.
Synthesis of Platinum-Rare Earth Metal Alloy Catalysts for Proton Exchange Membrane Fuel Cells
Authors: Zhou Quan , Hu Yang , Brandes Benedikt Axel , Cleemann Lars , Jensen Jens Oluf , Li Qingfeng
Published: July 2022

Electrocatalysts for low temperature fuel cells are based on noble metals and can be promoted by development of alloys of platinum with e.g. late transition metals such as Ni and Co.[1,2] It has been reported that Pt alloys with rare earth (RE) metals exhibit remarkable activity and high stability towards the oxygen reduction reaction.[3] Due to the very low standard reduction potentials and high oxophilicity of rare earth metals, preparation platinum alloys in form of nanoparticles meets great challenges for chemical routes of co-reduction. A one-step method is recently developed to prepare Pt−RE nanoalloys from a mixture of solid state precursors consisting of metal halides in their hydrate forms, a suitable nitrogen-rich compound and a carbon support.[4,5] The synthesis involves in situ formation of a carbon-nitrogen network, onto which the two metals are atomically dispersed. The coordination with nitrogen sites stabilizes the metals, which, upon thermal decomposition under a mild reducing atmosphere, leads to the formation of Pt-RE nanoalloys. The carbon support is introduced either as carbon blacks or carbon supported platinum powder. The pre-formed, either in or ex situ, platinum nanoparticles, facilitates the reduction of rare earth metals thermodynamically driven by the negative alloying free energy. A series of pure crystal phases such as Pt5RE (e.g. La, Ce, Nd), and Pt3RE (e.g. Y, Gd, Tb) have been synthesized in form of carbon supported nanoparticles with tunable metal loadings and alloy particle sizes. One of the typical catalysts is the Pt5Ce/C in a metal to carbon ratio of 30 wt% and an average alloy particle size of ca. 5.5 nm which exhibits an area specific activity of 3.7 times and a mass activity of 1.9 times higher than those of the Pt/C analogue. Further understanding and improvement of the process are in progress and the updated results will be presented in this talk.

[1]. J. K. Norskov et al., Nature Chemistry 1, 37-46 (2009)

[2]. X. Q. Huang et al., Science 348, 1230-1234 (2015)

[3]. M. Escudero-Escribano et al., Science 352, 73-76 (2016)

[4]. Y. Hu et al., J. Am. Chem. Soc. 142, 953–961 (2020)

[5]. Y. Hu et al., Chem. Mater. 33, 2, 535–546 (2021)
Sacrificial Template-Assisted Mechanochemical Production of Highly Active Bifunctional Fe-N-C Catalysts
Authors: Alimbekova Amina , Kosimov Akmal , Yusibova Gulnara , Aruväli Jaan , Käärik Maike , Leis Jaan , Kongi Nadezda
Published: July 2022

Bifunctional catalyst materials development for energy storage and conversion technologies is notoriously demanding in terms of electrochemistry (low stability, sluggish kinetics and high total overpotential (∆E)) and logistics (environmental safety, production methodologies and cost).

Noble metal electrocatalysts are proven to be good bifunctional catalysts and as a result are being used as benchmark catalysts. However, the environmental and economic sustainability is severely compromised due to the scarcity of these metals. The alternative option is based on first-row transition metal heteroatom-doped carbon materials. Low cost, high availability, great electrocatalytic activity and stability promise to be a suitable noble metal free catalyst for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR).

This work showcases a high performance Fe-N-C type material with sustainable synthesis and efficient activity towards ORR and OER. Unlike various classical methods for electrocatalyst synthesis, the developed methodology combines mechanochemistry and application of sacrificial template, which yields materials with superior bifunctional oxygen electrocatalytic performance.
(Digital Presentation) Temperature-Dependent Study for Hydrogen Permeability of a Polymer Electrolyte Membrane Used in a PEFC
Authors: Celi Manuel , Santana Jordy , Espinoza Andaluz Mayken , Andersson Martin
Published: July 2022

Great efforts are currently underway to improve the performance of Polymer Electrolyte Fuel Cells (PEFCs) since they are potential devices to move on towards a carbon-free future. The Polymer Electrolyte Membrane (PEM) is crucial for the PEFC. It is the site where the exchange of protons between the anode and the cathode occurs to complete the energy conversion process. Also, operation temperature is one of the most critical parameters that significantly affect the internal reactions and thus the performance too. For this reason, it is essential to evaluate its performance at different temperatures. One useful technique is the linear sweep voltammetry (LSV) test. This technique allows knowing the hydrogen crossover that passes through the PEM and the existence of a short circuit. The determination of the hydrogen crossover is of great relevance since the conduction of electrons through the PEM causes a decrease in the fuel cell efficiency. Linear sweep voltammetry is an electrochemical method where the voltage is varied linearly as a function of time, and a current response is measured by a potentiostat. The analyzed single fuel cell features an effective area of 25 cm2, a polymer electrolyte membrane of Nafion® 112. The temperature was varied from 30 to 80 °C to cover the most common temperatures during operation, with a settled relative humidity at 100%. Hydrogen was used on the anode side and nitrogen on the cathode, with 0.1 L / min flow. The results show a proportional relationship between the crossover and the cell's operating temperature; with the data set, correlations were obtained using the fitting tool of Matlab, reaching an R-squared close to one. The correlations obtained can predict the crossover through the membrane as a function of the operating temperature. Furthermore, it was determined that the short-circuit value also increases as the temperature increases. Based on this, an optimal temperature range is identified to guarantee the membrane degradation and losing efficiency as slower as possible.

Figure 1
Highly Stable Pt-Zn Intermetallic Oxygen Reduction Catalysts Supported on MOF-Derived Carbon for Proton Exchange Membrane Fuel Cells
Authors: Lee KwangHo , Bak Junu , Lee SangJae , Roh JeongHan , Cho EunAe
Published: July 2022

Commercialization of polymer electrolyte membrane fuel cells (PEMFCs) requires a dramatic reduction in the price of catalysts, which account for a significant portion of the total cost. Therefore, since most catalysts in PEMFCs are present in the cathode where the oxygen reduction reaction (ORR) occurs, it is necessary to ensure sufficient durability after the reaction and activity of the catalysts for the ORR. In this work, using metal-organic framework (MOF)-based carbon supports, platinum (Pt) catalysts were converted into platinum-zinc (Pt-Zn) intermetallic catalysts to enhance the durability of the catalysts, moreover, the additional interaction was introduced between nanoparticles and supports, improving the stability of the catalyst. High-magnification transmission electron microscopy and X-ray diffraction analysis confirmed the ordered structure of intermetallic Pt-Zn nanoparticles. In the half-cell test, the mass activity and the specific activity of the L10-PtZn/Zn-NC catalyst were 3.8 and 5.7 times as great as that of commercial Pt/C, respectively. Furthermore, to evaluate the stability of the catalysts while the ORR condition, we conducted the durability cycles from 0.6 V to 1.0 V versus RHE. After the durability cycles of 30k, the electrochemically active surface areas (ECSAs) of the L10-PtZn/Zn-NC(103.1% of the initial ECSA) showed significantly enhanced stability compared to that of the commercial Pt/C(66.2% of the initial ECSA). This work provides us a new strategy to obtain the high stability of the intermetallic catalysts as well as the enhanced activity using MOF-derived carbon support.
Catalyst Layers Prepared By Mixing Ionomer Dispersions with Different Equivalent Weights in Proton Exchange Membrane Fuel Cells
Authors: Park Jong Hyeok , Kim Beom-Seok , Park Jin Soo
Published: July 2022

Recently, hydrogen-based energy conversion devices are stand out in the world for decarbonization. Fuel cells are common devices for hydrogen utilization, membrane electrode assembly (MEA) has the most important role in all components for fuel cell performance. MEA is consist of membrane and both side of catalyst layer, the catalyst layers were made of electrocatalyst and ionomer by evaporating all solvents in the catalyst inks. The ionomer increases the catalyst utilization by covering the electrocatalyst in the catalyst layer and increases the gas penetration by forming pore in the catalyst layer. Each ionomer dispersion has a different EW, and there are two types of side chains: Long side chain (LSC) and short side chain (SSC). Each ionomer has advantages and disadvantages. The structure of catalyst layer is formed differently according to type of ionomer, which could be make difference performance of catalyst layer. By mixing the ionomer, the advantages can be optimized to obtain a beneficial effect. Many properties of the components to consist of catalyst layers substantially influence their performance and durability due to the different interaction of electrocatalysts and ionomer. In this study, EW conducted an experiment to find out the difference in the properties of the catalyst layer using the same commercial ionomer and the ionomer made by mixing different dispersions. Three types of ionomers were used: i) long-side chain (LSC) ionomer, ii) short-side chain (SSC) and iii) Mixture of dispersions with different EW ionomer. Use an IEC automatic titrator to verify that ionomer dispersions made by mixing different ionomer dispersions have target EW values. Prepared catalyst layers prepared by the ionomers with different side chains were characterized by electrochemical evaluation such as I-V polarization, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and by physical and microscopic characterization such as porosimetry and water uptake.

Acknowledgments

This research was supported in part by the Hydrogen Energy Innovation Technology Development Program of the National Research Foundation (NRF) funded by the Ministry of Science, ICT ＆ Future Planning (NRF-2019M3E6A1063677) and by 2021 Green Convergence Professional Manpower Training Program of the Korea Environmental Industry and Technology Institute funded by the Ministry of Environment.
(Digital Presentation) ORR/OER Activity and Rechargeable Zinc-Air Battery Performance of B Site Doped Double Perovskite NdBaCoXO5+δ (X= Fe, Ni, Mn)
Authors: Özgür Çağla , Toparli Cigdem
Published: July 2022

Renewable energy systems and designing economically viable electrochemical energy storage systems is essential to decrease environmental pollution concerns while meeting the growing energy demand. Among the various energy storage devices, rechargeable zinc-air batteries (RZAB) have attracted great attention due to their relatively high specific energy (1218 W.h/kg), and volumetric energy density (6136 W.h/L) cost-effectiveness, and environmental friendliness, comparable to that of lithium–air batteries [1]. However, the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during the discharge and recharge process of the air cathode on RZAB prevents large-scale application. So far noble metals (Pt, Ru, Ir) and their alloys (Pt-Ru/C) are used as bifuctional oxygen electrocatalysts in commercial rechargeable RZAB, yet they are too expensive to be viable for large-scale commercial applications. Therefore, designing robust and cost-effective bifunctional oxygen electrocatalysts is prime of importance for RZAB to be commercialized [2]. One of the most promising oxygen bifunctional catalyst are perovskite oxides due to their structural and compositional flexibility [3]. Moreover, the electronic structure of perovskite oxides can be tuned by varying the transition metals at the B site and thus their electrocatalytic performance [4-5].

In this work, first we will demonstrate phase pure fabrication of double perovskite oxide series of NdBaCoXO5+δ (X= Fe, Ni, Mn). Second, OER and ORR performances of the series of NdBaCoXO5+δ (X= Fe, Ni, Mn) will be explained in relation with their electronic structure and work function. Here, we applied NdBaCoMnO6 on a home-made RZAB as air cathode, according to its bifunctional index. Therefore, we will finally present charge-discharge performance of RZAB with NdBaCoMnO6 as air cathode.

J. Fu, Z. P. Cano, M.G. Park, A. Yu, M. Fowler, Z. Chen, Advanced Materials, 29, 1604685 (2016).

Y. Tong, J. Wu, P. Chen, H. Liu, W. Chu, C. Wu, Y. Xie, Journal of the American Chemical Society, 140, 11165-11169 (2018).

W. Yin, B. Weng, J. Ge, Q. Sun, Z. Li, Y. Yan, Energy & Environmental Science, 12, 442-462 (2019).

J. Ahmed, N. Alhokbany, M. Ubaidullah, S. Mutehri, M. M. Khan, S. M. Alshehri, Ceramics International, 46, 20038-20044 (2020).

A. Mulder, N. Benedek, J. Rondinelli and C. Fennie, Advanced Functional Materials, n/a-n/a (2013).
(Digital Presentation) The Optimization of Polypyrrole Concentration to Synthesize Hollow Fe, Co, and Nitrogen Doped Carbon Spheres with Improved Oxygen Reduction Reaction Performance
Authors: Quoc Hao Nguyen , Kim Jinsoo
Published: July 2022

Transition metal and nitrogen co-doped carbon materials (M-N-C, M=Fe, Co, Ni, etc.) have recently emerged as front runners to replace commercial Pt/C for the oxygen reduction reaction (ORR) due to their natural availability and excellent electrocatalytic activity. The development of M-N-C materials with optimized active sites using a secondary nitrogen source has attracted a lot of attention as ORR catalysts for their high activity and excellent durability. Polypyrrole (PPy) has become an attractive secondary nitrogen source for increased nitrogen doping and metal dispersion. Herein, we developed hollow Fe, Co, and nitrogen-doped carbon (H-FeCo-NC) spheres using the composites of metal-organic frameworks (MOFs) materials and PPy. Based on X-ray absorption fine spectroscopy analysis, X-ray photoelectron spectroscopy, and transmission electron microscopy, the active centers and the role of PPy for ORR catalytic performance are explored. The H-FeCo-NC not only displayed remarkable ORR performance in alkaline media, with a half-wave potential of 0.903 V, but also showed excellent stability and durability. The results outperformed the commercial Pt/C catalyst, demonstrating the potential of utilizing PPy for improved ORR performance.
3D Printed Carbon Aerogels for Polymer-Electrolyte Fuel Cells
Authors: Santamaria Anthony D. , Chandrasekaran Swetha , Philbrick Oliver , Worsley Marcus Andre
Published: July 2022

Carbon aerogels (CA) are known for ultra-low density, very high surface area, fine porous structure, and excellent electrical conductivity. Recent advances in high resolution 3D printing at LLNL enable the manufacturing of complex CA structures which have been demonstrated for electrolysis, flow battery, and supercapacitor applications. Polymer-electrolyte fuel cells (PEFC) may be an excellent candidate for these materials/methods as designers seek to optimize membrane-electrode assemblies to achieve higher power densities. A major challenge to PEFC design is two-phase flow due to water production which causes pore flooding and leads to cell instability. To mitigate these effects, groups have investigated the creation of liquid specific pathways in the porous layers to alleviate liquid buildup and enhance gas diffusion. Methods employed include the addition of small holes to the gas-diffusion layer (GDL) for liquid drainage as well as porosity gradients to exploit capillary effects. While some progress has been made, traditionally manufactured GDLs, which consist of randomly distributed carbon fibers, are limiting. 3D printed CAs are a promising solution as complex macroporous electrode structures can be manufactured out of microporous filaments with a high level of control. Additionally, the process may allow for the consolidation of multiple layers (MPL, GDL, & flow channels) into a single printed architecture. In this work various CA lattice structures were printed using a direct ink write (DIW) method and breakthrough pressures were measured to demonstrate the ability to tune the liquid pathways to achieve specific pressure thresholds. A discussion of the prospects for printed CA electrodes in PEFC will focus on material properties, synthesis techniques, and current challenges.

*anthony.santamaria@wne.edu
Influence of the Electrode-Electrolyte Interface on the Product Distribution of the HMF Electroreduction
Authors: Kloth Ricarda , Vasilyev Dmitry V. , Mayrhofer Karl J. J. , Katsounaros Ioannis
Published: July 2022

The electrochemical reduction of 5-hydroxymethylfurfural (HMF), a biomass-based platform chemical, is a promising route towards the defossilization of the transportation sector. It yields fuels, such as 2,5-dimethylfuran (DMF), and fuel precursors, such as 2,5-dihydroxymethylfuran (DHMF) and 5,5’-bis(hydroxylmethyl)hydrofuroin (BHH), while requiring only renewable resources. In order to control the selectivity of this reaction and to optimize the yield of the desired target compound, it is important to understand the reaction mechanisms towards the individual products and the influence of various system parameters. We utilize two complementary methods, namely electrochemical real-time mass spectrometry (EC-RTMS) and quantitative batch electrolysis in a flow reactor, to obtain further insights into the electrochemical HMF reduction mechanisms and the interplay between the electrode and electrolyte. While EC-RTMS is a fast screening technique, which allows for the analysis of transient processes, the batch electrolysis in the flow reactor enables product quantification by high-performance liquid chromatography (HPLC) and gas chromatography (GC) and the calculation of reaction selectivities and faradaic efficiencies. With these techniques, we were able to investigate the influence of various system parameters, such as the electrode material, the applied potential and the composition of the electrolyte, on the product distribution and propose reaction mechanisms towards the individual products.[1]

References

[1] R. Kloth, D. V. Vasilyev, K. J. J. Mayrhofer, I. Katsounaros, Electroreductive 5-Hydroxymethylfurfural Dimerization on Carbon Electrodes ChemSusChem
2021, 14, 5245.

Figure 1
(Invited) Optimization of Z-Scheme Photocatalytic Reactors for Solar Water Splitting
Authors: Chen Zejie , Keene Sam , Gaieck William , Phun Gabriel S. , Stinson Robert , Stinson William D. H. , Wang Yinxian , Barrera Luisa , Chen Zijie , Mayer Mike , Watanabe Kenta , Kim Tea Yon , Zutter Brian , Lapp Aliya S. , Xu Mingjie , Acevedo Yaset , Huya-Kouadio Jennie , James Brian , Kudo Akihiko , Pan Xiaoqing , Hurst Katherine , Talin Alec Alec , Esposito Daniel V. , Bala Chandran Rohini , Ardo Shane
Published: July 2022

The U.S. Department of Energy recently announced its first Energy Earthshot on Clean Hydrogen, with a cost target of $1/kg-H2 by 2031. Assuming future utility-scale grid electricity prices from photovoltaics ($0.02/kWh), 80% of the cost of H2 would come from performing low-temperature water electrolysis at its thermoneutral voltage, with zero additional overpotential. This fact motivates alternative, less-expensive means of using light to generate mobile charge carriers than photovoltaics, and reactor designs with exceedingly low capital costs, which we recently invented. Systems that use low capital cost reactors benefit from low-voltage operation, which represents a paradigm shift from current state-of-the-art electrolyzers that aim to operate at high current densities. Analytical models predict that solar photocatalytic water splitting inherently exhibits such low-voltage operation through use of an ensemble of optically thin photoabsorbers, which results in larger overall solar-to-hydrogen conversion efficiencies in comparison to optically thick designs. In efforts to attain these predicted higher efficiencies, we are performing detailed studies on the properties of state-of-the-art doped SrTiO3 photocatalyst particles. During my talk, I will share our recent efforts in atomic-layer deposited ultrathin oxide coatings to impart redox selectivity and materials stability, single-photocatalyst-particle current–potential behavior and mobile charge carrier properties, and atomic-level information on dopant distributions and materials interfaces obtained from electron microscopies and X-ray spectroscopies. Collectively our discoveries provide new design guidelines and additional research pathways for the development of effective composite materials to serve as active components in techno-economically viable artificial photosynthetic devices.
(Invited) A Novel Co-Doping Strategy for Efficient Solar Water Splitting
Authors: Jang Ji-Hyun
Published: July 2022

In general, doping of hematite increases photoelectrochemical (PEC) water splitting activity by enhancing the bulk conductivity of the photoanode. In this presentation, I report the negative interaction of the two dopants (Sn and heteroatom) in co-doped hematite that was neglected before. We developed an easy heteroatom-doping method that suppressed Sn doping from the FTO substrate. The co-doped hematite converted the incident photons to EHPs with much reduced recombination and exhibited an excellent photocurrent density greater than 4 mA cm-2 at 1.23VRHE and an outstanding low turn-on voltage, which is closer to the theoretical efficiency of hematite. Our co-doping strategy provides a straightforward way to addressing the chronic short-hole diffusion length issue that causes a high electron hole recombination rate, to potentially improve the performance of PEC devices.
(Invited) Bulk Heterojunction Organic Semiconductor Photoelectrodes and Photocatalysts for Solar-Driven Water Splitting
Authors: Sivula Kevin
Published: July 2022

The bulk heterojunction (BHJ) concept, which has been successfully developed for organic semiconductor-based photovoltaic devices, offers a promising route to high-performance and inexpensive photocatalyst nanoparticles for solar hydrogen production. However, the suitability organic semiconductors (OSs) towards robust and high efficiency photocatalytic water splitting remains an open question. Herein, efforts to understand the stability of OS-based BHJ photoelectrodes for both solar driven water reduction [1] and oxidation [2] are discussed. The integration of a BHJ photoanode and photocathode into a bias-free solar-driven water splitting device is also reported. Finally, the important aspects needed for translating these systems into nanoparticle photocatalysts are examined.

______________

References:

[1]L. Yao, N. Guijarro, F. Boudoire, Y. Liu, A. Rahmanudin, R. A. Wells, A. Sekar, H.-H. Cho, J.-H. Yum, F. Le Formal, K. Sivula, J. Am. Chem. Soc.
2020, 142, 7795.

[2] H.-H. Cho, L. Yao, J.-H. Yum, Y. Liu, F. Boudoire, R. A. Wells, N. Guijarro, A. Sekar, K. Sivula, Nat. Catal.
2021, 4, 431.
Non-Adiabatic Dynamics Simulation of Plasmon-Mediated Chemistry
Authors: Zhang Yu
Published: July 2022

Localized surface plasmon resonances (LSPRs) have attracted much recent attention for their potential in promoting chemical reactions with light. However, the mechanism of LSPR-induced chemical reactions is still not clear and suffers from many controversies. This presentation will discuss the atomic-scale mechanism of plasmonic hot-carrier mediated chemical reaction exampled by H2 dissociation by employing time-dependent density functional calculations theory and non-adiabatic molecular dynamics. The key observation is that there are nested excited states corresponding to both hot-electron excitation and charge transfer [1]. These nested states cross, facilitating the transitions depicted in the desorption induced by the electronic transitions model and the surface hopping model. I believe this is the first time that such a connection has been made based on a first-principles calculation. Diabatization of these states shows that the charge transfer states are responsible for H2 dissociation, while the hot electron states do not. Previous works only identified the hot electron states, thus were unable to explain the dissociation in a convincing way. Moreover, we also found chemical reaction is tunable if the molecule is placed in the center of the plasmonic dimer [2]. The reaction rate can be either suppressed or enhanced depending on the geometry.

[1] Q. Wu, L. Zhou, G. C. Schatz, Y. Zhang*, H. Guo*, J. Am. Chem. Soc. 2020, 142, 13090–13101.

[2] Y. Zhang*, T. Nelson, S. Tretiak, H. Guo, G. C. Schatz. ACS Nano,
2018, 12, 8415-8422.
Recent Advancements in Morphologies of TiO2 Nanotube Layers and Their Photocatalytic Performance
Authors: Sepúlveda Sepúlveda Lina Marcela , Saldan Ivan , Sopha Hanna , Macak Jan M.
Published: July 2022

Self-organized TiO2 nanotubes arrays, formed by electrochemical anodization of Ti, have attracted tremendous scientific and technological attention, due to their remarkable properties such as the tunability of dimensions, their directionality, high surface area, low density, and ability to absorb significant amount of incident light [1,2].

The most widely used electrolyte for the synthesis of TiO2 nanotube layers is based on ethylene glycol containing small amounts of water and fluoride ions. However, nanotubes prepared in these electrolytes present a double-walled structure, with the outer wall consisting of almost pure TiO2 and the inner wall consisting of TiO2 contaminated with carbon and fluoride species [3,4]. In the recent years, the selective etching of the inner nanotube wall on Ti layer enabled synthesis of single-wall nanotubes that showed a superior photo-electrochemical performance compared to their double-walled counterparts [5]. An extensive etching enabled also the synthesis of single tube powders, which could be effectively decorated with Fe3O4 nanoparticles to act as magnetically guidable photocatalyst [6,7].

The presentation will focus on the influence of all these nanotube morphologies on the photocatalytic degradation in the liquid phase. In particular, we will discuss, how the annealing temperature of single nanotubes influences their photocatalytic performance [7] and how the wall thickness of the single wall nanotubes can be optimized for the best performance [8]. Experimental details and photocatalytic results will be presented and discussed.

References:

[1] J. M. Macak et al., Curr.
Opin. Solid State Mater.
Sci.,
2007, 1-2, 3.

[2] K. Lee et al., Chem. Rev
.,
2014, 114, 9385.

[3] S.P Albu et al., Adv. Mater.
2008, 20, 4135.

[4] A. Dronov et al., Appl. Surf. Sci.,
2018, 434, 148.

[5] M. Motola et al., Electrochem. Commun
.,
2018, 97, 1.

[6] D. Beketova et al., ACS Appl. Nano Mater
.,
2020
, 3, 155.

[7] M. Sepuvelda et al., Ms in preparation.

[8] M. Motola et al., Appl. Surf. Sci.,
2021, 549, 149306.
NiO Modified CN Film As Photoanodes for Photoelectrochemical Water Oxidation
Authors: LIU Chang , Liu Jian , Godin Robert
Published: July 2022

The utilization of solar energy, by far the most promising renewable energy resource, remains one of the hottest topics in the 21st century. Metal-free carbon nitride (CN) material emerged as a promising water splitting photocatalyst in 2009 due to its appropriate visible light absorption, suitable optical band gap energy (2.7 eV), and facile synthesis. Though CN is one of the leading materials for solar energy conversion, this material is limited by light absorption, rapid charge recombination, and low charge carrier mobility. Metal oxide are thus investigated for counterbalancing CN’s inherent drawbacks. Interfacial CN/metal oxide heterostructures facilitate charge transportation, resulting in improved sunlight-driven water splitting process. In this work, low-cost NiO transition-metal oxide material was applied to speed up the sluggish kinetics of the oxygen evolution reaction (OER). Typically, CN modification is achieved by traditional hydrothermal approach, while its disadvantages such as uneven coating particle size and heterogenous distribution are becoming increasingly apparent. Aiming at a conformal morphology, atomic layer deposition (ALD) is developed as the state-of-the-art technique. It has boosted the depositing accuracy by achieving precisely depositing thickness and extremely homogenous surface. In our process, a uniform CN film was deposited on FTO substrates using a dipping-drying technique with a hot saturated thiourea aqueous solution followed by a thermal treatment. Then plasma-enhanced atomic layer deposition (PEALD) was used to modify the CN film with a thin layer of NiO. PEALD controls the NiO modification on a fine-scale, allowing to with deposit a nanoscale NiO layer on the CN surface while exposing adequate CN photoreactive sites. According to our results, the modified NiO/CN heterostructure has the potential to improve photoelectrochemical water oxidation as a photoanode in alkaline solution. From the morphology side, the NiO loaded flake-like CN creates relatively high specific area for OER. Then we investigated the photo-process kinetic using a series of optical and spectroelectrochemcial techniques. Optical absorption is enhanced, showing stronger visible light absorption up to 700 nm. Fast charge separation is suggested in photoluminescence (PL) characterization. Superior (photo)electrochemical (PEC) activity is foreseen through PEC and EC measurements. To conclude, this is the first time we succeed to modify the CN film with the ALD technique for solar-driven water oxidation, and has the highly possibility of reaching the photo(electro)chemical performance new level.
(Invited) Engineering Challenges in Scaling-up Solar Water Splitting Devices
Authors: Abdi Fatwa
Published: July 2022

The last decade has witnessed significant progress in the development of solar water splitting devices, with solar-to-hydrogen (STH) efficiency as high as 30% already demonstrated. However, two major challenges remain. First, the high-efficiencies (> 15%) have only been achieved using devices based on expensive and non-scalable III-V semiconductors. On the other hand, low-cost metal-oxide based devices, mainly using BiVO4 as the absorber, have only achieved STH efficiency of < 10%. Due to stability limitations, many of these metal-oxide based devices are operated in near-neutral pH electrolytes, which presents an additional mass transport challenge. Second, the majority of the demonstrated devices are still at the laboratory scale. Reports on large-area devices start to emerge, but they typically show much lower efficiencies. This is best illustrated in a recent review:[1] even when III-V semiconductor-based devices are considered, there is no report of devices with a semiconductor absorber area larger than 10 cm2 and STH efficiency > 10%.

In this talk, we will discuss the scale-up of our photoelectrochemical water splitting devices based on a complex metal oxide photoabsorber. Factors other than the semiconductor photoabsorber itself are found to be responsible for a total voltage loss of > 500 mV and therefore limit the overall performance of the large-area device.[2] To properly address this limitation, we quantify and break down the different loss mechanisms associated with the device scale-up and the practical operational conditions.[3] Concentration overpotential due to pH gradient is found to be a major contributor to the performance loss, and we show using multiphase multiphysics simulations and in-situ fluorescence measurements that careful control of natural and forced convection can overcome this limitation.[3-5] In addition, we also explore the possibility to achieve efficient product separation in devices with and without separators. The product crossover, optical and Ohmic losses are quantified using a combination of experiments and simulations, and the optimization of the device working parameters and/or separator properties to achieve the minimum overall loss will be discussed.[6,7]

References

J. H. Kim et al., Chem. Soc. Rev. 48, 2019, 1908

I. Y. Ahmet et al., Sust. Energy Fuels 3, 2019, 2366

F. F. Abdi et al. Sust. Energy Fuels 4, 2020, 2734

K. Obata et al. Energy Environ. Sci. 13, 2020, 5104

K. Obata & F. F. Abdi, Sust. Energy Fuels, 5, 2021, 3791

K. Obata et al. Cell Rep. Phys. Sci. 2, 2021, 100358

C. Özen et al. in revision
(Invited) Tailored Electrochemical Interfaces for the Production of Renewable Fuels
Authors: Escudero-Escribano Maria
Published: July 2022

Tailoring the structure of the electrochemical interface at the atomic level is key to design new electrocatalysts for renewable energy conversion and storage. This talk will focus on novel catalyst materials and engineered interfaces for electrochemical energy conversion. In particular, I will discuss structure sensitivity and electrolyte effects for oxygen and carbon dioxide/carbon monoxide electrocatalysis.

First, I will present our work toward understanding the structure-activity-stability relations on high surface area nanostructured Ir-based materials for oxygen evolution. Then, I will highlight the importance of carrying out model studies on Cu-based surfaces to understand the structure-properties relations for CO2 and CO reduction. We have investigated the effect of pH, specific anion adsorption and potential dependence for CO reduction on Cu single-crystalline electrodes. We show how well defined studies are essential to design efficient electrocatalysts for the production of renewable fuels.
Tuning CO2 to CO Conversion on Metal-Doped Carbon Catalysts
Authors: Sarma Saurav Chandra , Barrio Jesus , Titirici Magda , Stephens Ifan Erfyl Lester
Published: July 2022

One of the significant challenges faced during electrochemical CO2 reduction (ECO2RR) is the low selectivity of the products obtained. The best example is polycrystalline Cu, which can electrochemically produce hydrocarbons and alcohols but with poor selectivity.1, 2 To date, high selectivity has been achieved only towards CO and formate on Au and Sn surface, respectively but scalability and commercialization are limited owing to their cost and stability. Metal-nitrogen-carbon (MNC) materials are comparable to Au or Ag catalysts, albeit with their lower overpotentials, higher mass activity and high selectivity toward CO.3
,
4 During the pyrolysis of N-containing carbon molecules, different chemical functionalities such as pyridinic, pyrrolic and graphitic N atoms can be formed, each behaving as a product-specific active site. 5 It is still debatable whether pyrdinic or pyrrolic N is responsible for CO2RR activity; thus, it remains unclear how to favor CO2 reduction over hydrogen evolution.

In this work, we aimed to synthesize C2N-like covalent organic frameworks, with 8-10 Å pore size, tailored to host dual atoms coordinated to nitrogen. Such sites are expected to favor C-C coupling and produce multi-carbon products during ECO2RR. A step-by-step synthetic approach was employed to optimize the CO2RR:HER ratio through:

Tuning carbon:nitrogen ratio using two different synthetic approaches.

Reducing nitrogen in the carbon matrix through pyrolyzing at different temperatures (700, 800 and 900 oC),

Doping phosphorus and nitrogen into the carbon matrix

Tuning CO2RR product distribution through different metals (Fe and Ni) doping.

EXAFS and STEM studies revealed the presence of a mixture of single and dual atomic sites. XPS and ICP results showed that Fe and Ni loadings <2 wt% could be obtained in the C2N materials. Higher hydrogen evolution, owing to the higher N-content, was observed at a lower pyrolysis temperature which decreased at a pyrolysis temperature of 900 oC. Both Fe-NC and Ni-NC selectively produced CO, thus suppressing FE
H2 to <5%. Fe-NC also exhibited lower overpotential for CO production compared to its Ni-NC counterpart. A small percentage of ethanol and 2-propanol (FE<5%) was observed indicating the favoured C-C coupling on the dual-atomic sites. Further optimization of the metal-N coordination environment may allow for an improved selectivity for >C2 products.

References

K. P. Kuhl, E. R. Cave, D. N. Abram and T. F. Jaramillo, Energy Environ. Sci., 5, 7050 (2012).

S. Nitopi, E. Bertheussen, S. B. Scott, X. Liu, A. K. Engstfeld, S. Horch, B. Seger, I. E. L. Stephens, K. Chan, C. Hahn, J. K. Nørskov, T. F. Jaramillo and I. Chorkendorff, Chem. Rev., 119, 7610 (2019).

A. S. Varela, N. Ranjbar Sahraie, J. Steinberg, W. Ju, H.-S. Oh and P. Strasser, Angew. Chem. Int. Edit., 54, 10758 (2015).

A. S. Varela, W. Ju, A. Bagger, P. Franco, J. Rossmeisl and P. Strasser, ACS Catal., 9, 7270 (2019).

Y. Lum and J. W. Ager, Nat. Catal., 2, 86 (2019).