bluuebunny/crossref_metadata_2025 huggingface dataset:
The Positive Effects of Carbon-Coating Layers on Protecting the Nanoparticle Towards Poisoning Ions or Gases
Authors: Doan Huong , Sgarbi Ricardo , Labarde Quentin , Chatenet Marian
Published: February 2024

Recently, the research that explores the positive effects of carbon-coating nanoparticles to fight the severe oxidation/corrosion in Alkaline fuel cell (AFC), Proton-exchange membrane fuel cell (PEMFC) or water electrolyzer is well-recognized, since the carbon layers can extend the catalyst’s durability towards hydrogen oxidation/evolution reactions (HOR, HER) and oxygen evolution/reduction reactions (OER, ORR). Especially for the reactions in alkaline pH, with the graphite coating, the Ni nanoparticles in both HOR and HER can resist passivation and hydride poisoning. [1,2] Similarly, in the same alkaline conditions, the amorphous carbon coating slows down the degradation of Pd catalysts.[3] Moreover, the coating can block big ions such as halide, thus benefiting Pt group metals from resisting halide adsorption, that eventually prevents the dissolution of metal.[4,5]

In this work, we examined the gas poisoning effects on coated catalysts. For example, we synthesized carbon-coated Pd-Ni nanoparticles, supported on Vulcan carbon and studied its electrochemical response in 0.1M KOH at room temperature and its tolerance towards CO gas. As a result, Pd-Ni coated had better resistance to passivation compared to the non-coated Pd-Ni catalyst. It also showed that the thickness of the carbon coating layers was sufficient to block the CO absorption in RDE condition initially (Figure 1, black solid line). Only after 150 cycles of accelerated stress test in Ar (AST-Ar, using potential stepping between 0.1 and 1.23 V vs. RHE with a pulse of 3 s at each potential in Ar-saturated electrolyte, 6s/cycles), the passivation that occurred at high potential could cause a small portion of Pd to be “exposed” and adsorb CO (Figure 1, red solid line). After another 150 cycles of AST-Ar (AST 300), more Pd was exposed to CO adsorption but not fully. This proves the carbon-coating layers can protect the nanoparticles from poison contaminant gas such as NOx, SOx, CO, or the COx-like species. Both AFC and PEMFC systems can benefit from this type of catalyst to operate extensively without losing catalytic activity to passivation or pollution issues.

References

[1] Gao, Y. et al. ACS Appl. Mater. Interfaces
2020, 12 (28), 31575–31581.

[2] Doan, H. et al.
J. Electrochem. Soc. 2021 168 084501

[3]Sgarbi, R., Doan, H. et al.
Electrocatalysis
2022.

[4] Lin, G. et al.
J. Electrochem. Soc. 2016, 163 (1), A5049–A5056.

[5] Mukerjee, S., Doan ,H. et al. - US Patent 10,784,518, 2020

Figure 1
Anion Exchange Membrane Using Fused Expanded Pyridinium As Their Cationic Unit
Authors: Fujigaya Tsuyohiko , Motoishi Yuki , Kim Chaerin , Tanaka Naoki
Published: February 2024

Ion conductivity is expressed as a function of the Faraday constant, ion concentration, and mobility. Thus, an increase in both ion concentration and mobility is crucial for increasing the ion conductivity. Ion mobility reflects ionic motion in the restricted area of ion conduction channels. The general approach to expand ion conduction channels in AEM is to introduce a large number of ionic groups, i.e., to increase ion-exchange capacity (IEC). Because the increase of IEC also increase ion concentration, increase of IEC have been major strategy for increasing ion conductivity. However, this approach causes softening of the AEM because high IEC involves large amount of water uptake (WU).

On the other hand, the ion concentration in AEM is also affected by the dissociation constant of the ionic groups. However, conventional ionic groups in AEMs, such as ammonium cations, suffer from a low dissociation constant that leads to low ion conduction in AEM. Previously, we found that a fused expanded pyridinium cation (FEP) having a delocalized positive charge showed high dissociation of OH– owing to the weak interaction between the soft acid (FEP) and the hard base (OH–) which can be explained based on the Pearson Hard Soft Acid Base (HSAB) principle. As the result, AEM with FEP unit exhibited excellent ion conductivity of 123.4 ±13.3 mS cm–1 at 80 °C with very low IEC (0.77 mmol g-1).

Recently, we synthesized alkylated fused expanded pyridinium (CxFEP) with alkyl chain lengths (x) of 0, 6, 12, and 18 and introduced into polymers as side chains for AEM applications. FEP is characterized by a large π cation that offers weak electrostatic interactions with anions such as hydroxide (OH–) ions and therefore leads to high OH– conductivity in AEM. CxFEP shows synergetic effect between the π-π interactions of FEP and van der Waals interactions of the alkyl chains and forms a strong assembly, particularly for C6FEP. On the other hand, when CxFEP was introduced into the polymers, C12FEP formed an ordered stacking assembly in the films, whereas the other polymers with shorter (C0 and C6) and longer (C18) alkyl chains exhibited no such ordered structure. For the AEM, all the polymers showed higher ion conductivities than that of commercial ammonium-based AEM, even with their low ion exchange capacities (IEC), probably because of their characteristic weak interactions between the FEP cation and OH–. In particular, the AEM with C12FEP showed the highest ion conductivity of 143.3 ± 27.3 mS cm-1 even with a very low IEC of 0.41 mmol g-1. In addition to the high ion dissociation of FEP, the molecular assembly of FEP provides ionic conduction paths. This study demonstrates the importance of high ion dissociation and formation of a conduction pathway for AEM with high conductivity.
Unveiling the Impact of Carbon Corrosion on the Degradation of Fe-N-C Catalyst Layers in Alkaline Media
Authors: Ku YuPing , Kumar Kavita , Khalakhan Ivan , Hutzler Andreas , Götz Carina , Lloret Segura Vicent , Ehelebe Konrad , Mayrhofer Karl J. J. , Thiele Simon , Boehm Thomas , Cherevko Serhiy
Published: February 2024

One of the most promising candidates to replace platinum group metal catalysts for oxygen reduction reaction (ORR) in fuel cells (FCs) is the sub-class of iron-nitrogen-carbon (Fe-N-C) catalysts. However, Fe-N-C materials considerably suffer from varied degradation mechanisms. [1-2] Compared to FC operating conditions, start/stop events where the cathodes experience anodic potential may be more damaging due to the carbon corrosion phenomenon. [3] The correlation between carbon corrosion and Fe dissolution rates has been reported in aqueous model systems in acidic media. [3] However, different carbon corrosion mechanisms are reported for acidic and alkaline media. [4] While anion-exchange membrane FCs (AEMFCs) have gained increased attention, studies on the effects of carbon corrosion on realistic AEMFC Fe-N-C catalyst layers are still missing.

In this work, using a gas diffusion electrode (GDE) half-cell coupled with inductively coupled plasma mass spectrometry (ICP-MS), [5] we observed that the rate of Fe loss significantly accelerates with rising potential (E > 1.0 VRHE), commonly experienced during the start/stop events. Increased temperature intensifies the rate of Fe leaching during carbon corrosion (see Figure 1), while the gas atmosphere (Ar or O2) shows a negligible influence. On the contrary, the subsequent Fe deposition and the drop of ORR activity depend on the presence of O2 and the varied temperature. Combining in situ and post-mortem analyses, we report how carbon corrosion in alkaline media degrades Fe-N-C catalyst layers in various atmospheres and at different temperatures. These insights can contribute to rational designs of AEMFCs' start/stop protocol and more robust Fe-N-C materials.

Figure 1. Fe-N-C demetallation during anodic potential holds (1.0 - 1.5 VRHE) in O2-saturated alkaline (0.1 M NaOH) environment at 22 ± 2 and 62 ± 2 ℃. (A) Potential profile. (B) The Fe dissolution rate normalized to catalyst loading.

References:

[1] Adabi, Horie, et al. Nat. Energy., 2021, 6.8: 834-843.

[2] Speck, Florian D., et al. JACS Au, 2021, 1.8: 1086-1100.

[3] Choi, Chang Hyuck, et al. Angew.
Chem. Int. Ed., 2015, 54.43: 12753-12757.

[4] Yi, Youngmi, et al. Catal. Today, 2017, 295: 32-40.

[5] Ku, Yu-Ping, et al. J. Am. Chem. Soc., 2022, 144.22: 9753-9763.

Figure 1
Manganese and Nitrogen Doped Biomass-Based Activated Carbons As Electrocatalysts for Oxygen Reduction and Water Splitting
Authors: Tamasauskaite-Tamasiunaite Loreta , Upskuviene Daina , Balciunaite Aldona , Simkunaite Dijana , Jasulaitiene Vitalija , Niaura Gediminas , Drabavicius Audrius , Vaičiūnienė Jūratė , Volperts Aleksandrs , Plavniece Ance , Dobele Galina , Zhurinsh Aivars , Colmenares-Rausseo Luis Cesar , Kvello Jannicke , Kaare Kätlin , Kruusenberg Ivar
Published: February 2024

In this study, an efficient manganese (Mn) and nitrogen (N) co-doped carbon materials were prepared using the three raw materials, namely alder charcoal (Mn-N-CAC), hydrothermally carbonised birch wood (Mn-N-CW), and black liquor (Mn-N-CBL). At first, biomass-based activated carbon materials were synthesized. Mn and N were co-doped in one step using the reaction mixture containing Mn2+ ions source, activated carbon material, and dicyandiamide (DCDA) in dimethylformamide (DMF). DMF was evaporated and the mixture was treated for 60 min at a temperature of 800 ºC. The specific surface area, morphology, structure, and composition of Mn-N-C were determined using BET, TEM, XPS, Raman, XRD, and ICP-OES. Activity of resulted Mn-N-C materials was evaluated for oxygen reduction (ORR) as well as for hydrogen and oxygen evolution (HER and OER) using linear-sweep voltammetry (LSV) with a rotating disk electrode (RDE) in alkaline media.

It was found that all Mn-N-C materials had a high specific surface area in the range of approximately of 1800 to 2200 m2 g-1 but the Mn-N-CBL presented a higher contribution of the mesopores in comaparison to Mn-N-CAC and Mn-N-CW which are similar. All synthesized Mn-N-C materials exhibit excellent electrocatalytic activity for ORR with the onset and half-wave potentials of approximately 0.88‒0.90 and 0.80‒0.84 V, respectively, showing the 4e‒ electrons transfer path in 0.1 M KOH solution. The Mn-N-C materials also show enhanced activity for HER and OER in alkaline media.

Acknowledgment

The “Sustainably Produced Carbon Nanomaterials for Energy Applications (SuNaMa)” benefits from a 988000 € grant from Iceland, Liechtenstein, and Norway through the EEA Grants. The aim of the project is to develop innovative, high-performance, highly conductive, electrocatalytically active, durable, cost-effective, and high surface area nanocarbon materials. Project contract with the Research Council of Lithuania (LMTLT) No. is S-BMT-21-12 (LT08-2-LMT-K-01-055).
Kinetic Insights into the Mechanism of Oxygen Reduction Reaction on Fe2O3 /C Composites
Authors: S. Arya Gopal , Anuroop E.P. , Muthukrishnan Azhagumuthu
Published: February 2024

Electrochemical energy storage and conversion systems are the appealing replacement for nonrenewable resources to provide clean and sustainable energy. Of particular interest are fuel cells and metal-air batteries, both of which rely on the oxygen reduction reaction (ORR) for their operation. Fe-N-C catalyst has been widely used as a prominent catalyst towards ORR, but there is still some ambiguity regarding its active sites. This study describes the role of Fe2O3, an inevitable species formed in Fe-N-C catalyst towards the ORR. The Fe2O3 is carefully synthesised on various carbon supports and characterised using XPS spectra, HRTEM images, and surface area analysis. The particle size of the Fe2O3 nanoparticles synthesised on the pores of the carbon support was determined to be ~10 nm from the HRTEM analysis. The current density of ORR and the number of electrons transferred on Fe2O3/C catalysts is increased compared with bare carbon supports. Based on the kinetic analysis, the ORR on Fe2O3/C follows pseudo-4-electron (or) 2+2-electron ORR, where the first 2-electron ORR to H2O2 and second 2-electron H2O2 reduction reaction (HPRR) to H2O are assigned to the graphitic carbon (carbon defects) and Fe2O3 active sites, respectively. The role of Fe2O3 is further studied using the Theoretical method, which reveals the decreased formation of free energy of O2 adsorption. The Fe2O3 reduces the energy barrier for the reduction of *OOH to OH-. The Fe2O3/C shows higher stability by retaining 95% of the initial activity even after 20,000 cycles.

Figure 1
Transition Metal (Ni/Cu) Based Bimetallic Catalyst for Glycerol Oxidation
Authors: Gupta Saptarshi , De Mahuya
Published: February 2024

Alcohol fuel cell is considered as one of the most promising green energy generation option. Glycerol can be used as a potent fuel because of its excellent energy density, ready availability, financial viability and minimal toxicity. Moreover, glycerol is also an active petroleum by-product. In direct glycerol fuel cell, precious noble metal based catalyst was extensively used as electro-catalyst for glycerol oxidation. The use of noble metal as catalysts restricted the viable commercialisation due to its high cost. This study intended to use transition metal such as nickel and copper based monometallic and bimetallic catalyst for glycerol oxidation to lower down the cost of commercialisation. These metals already proved to be efficient catalyst for electro-oxidation of methanol and ethanol [1-2]. Carbon was already proved to prominent support material for electro-catalyst due to high surface area and superior conductivity.

The metals were impregnated into carbon support followed by reduction under H2/Ar environment with 20 wt % metal loading. The weight ratio of Ni and Cu in bimetallic catalyst was fixed as 1:1. The average metal particle size of the catalysts varied between 7.8 to 16.3 nm. The cyclic voltammetry of different catalysts for 0.5 M glycerol oxidation in 1 M KOH is shown in Fig 1a). The onset potential of bimetallic catalyst (NiCu/C) was reduced to 0.20 V compared to their monometallic counterpart (0.39 V for Ni/C and 0.42 for Cu/C). The glycerol oxidation peak was observed at 0.71, 0.73 and 0.78 V for Cu/C, Ni/C and NiCu/C respectively. The specific activity and mass activity was shown in Fig 1b). The highest specific (76 mA/cm2) and mass activity (775 mA/mgmetal) was obtained for NiCu/C from glycerol oxidation. The obtained electrochemical surface area (ECSA) was highest for NiCu/C (99 m2/g) followed by Ni/C (44 m2/g) and Cu/C (34 m2/g). The higher activity of NiCu/C could be attributed to the lower Tafel slope, higher ECSA and charge transfer co-efficient. The EIS results conveyed that electro-oxidation process was slower than charge transfer process. Moreover, lowest time constants for the both the process was observed for NiCu/C catalyst. Hence, NiCu/C proved to be efficient electro-catalyst with superior activity for glycerol oxidation in direct glycerol fuel cell.

Fig 1. a) Cyclic voltammetry of different catalyst in 0.5 M glycerol and 0.1 M KOH and b) Specific and mass activity of different catalyst.

References

[1] X. Cui, W. Guo, M. Zhou, Y. Yang, Y. Li, P. Xiao, Y. Zhang, X. Zhang, ACS Appl. Mater. Interfaces, 7 (1), 493-503 (2015).

[2] A. N. Vyas, G. D. Saratale, S. D. Sartale, Int. J. Hydrog. Energy, 45 (10), 5928-5947 (2020).

Figure 1
Trimetallic Alloy as an Electrocatalyst for Direct Low Temperature Fuel Cells: The Case of MF Oxidation on Pt3Pd3Sn2
Authors: Yadav Radhey Shyam , Schechter Alex , Kornweitz Haya
Published: February 2024

Methyl formate (MF) has been considered an attractive hydrogen carrier alternative fuel due to its high energy density, ease of storage and transport, and low boiling point (32o C @ 1 atmosphere) liquid. However, the low number of publications on efficient anodic catalysts is impeding the development of a direct methyl formate fuel cell (DMFFC).

In this study, a first-principles density functional theory (DFT) calculation was performed to study the MF electro-oxidation on the surface of the Pt3Pd3Sn2 (111) alloy. This surface was proven to be the most active in the anodic oxidation of other small organic molecules1,2. A detailed thermochemistry and kinetics study of MF oxidation was carried out to determine the active sites, most probable reaction pathway for the oxidation of CH3OCHO to CO2, and analyzed the dehydrogenation steps via direct (HCOOH pathway) and indirect (CO pathway) mechanisms.

The potential required for complete oxidation of MF to CO2 is 0.66 V. The study revealed that Sn plays an essential role in the mitigation of CO poisoning through water activation and surface oxide reaction mechanisms in a bifunctional manner. Furthermore, based on our findings, Pt and Pd work synergistically to enhance the utilization of active sites for the initiation of MF oxidation and promote HCOOH oxidation, which accelerates the kinetics of the electrochemical reaction.

References:

D. Kashyap et al., J Power Sources, 544, 231882 (2022).

M. G. Gebru, H. Teller, P. Subramanian, and A. Schechter, Energy Technology, 10, 2200835 (2022) https://onlinelibrary.wiley.com/doi/full/10.1002/ente.202200835.
Au-Based MOFs as Anodic Electrocatalysts for Direct Borohydride Fuel Cells
Authors: Belhaj Ines , Becker Alexander , Gusmão Filipe M.B , Šljukić Biljana , Chaves Miguel , Balula Salete S , Silva Luís Cunha , Santos Diogo M.F
Published: February 2024

Researchers are exploring direct liquid fuel cells (DLFCs) as alternatives to proton-exchange membrane fuel cells because of their higher energy density and ease of storing and transporting the fuel. Direct borohydride fuel cells (DBFCs) are of particular interest as they offer a sustainable energy source with their high-power density output and the use of a highly alkaline NaBH4 medium [1]. Ensuring efficient and cost-effective catalysts for DBFCs is crucial for their commercial viability. Metal-organic frameworks (MOFs) have demonstrated significant potential as anodic electrocatalysts for BOR in DBFCs [2]. However, research should explore various modifications to MOFs, such as the incorporation of alternative metal ions or functional groups, to improve their catalytic efficiency and reduce cost. This study evaluated the performance of newly developed MOF-based electrocatalysts for DBFCs. Specifically, six MOF-based materials were synthesized and analyzed for their ability to facilitate borohydride oxidation (BOR) using cyclic voltammetry and chronoamperometry in alkaline media. MIL-101_Au@NH2 and MOF-808_Au@NH2 were found to be highly effective for BOR. The kinetic parameters for BOR with MOF-based electrocatalysts, including activation energy, reaction order, exchanged electrons, and anodic charge transfer coefficient, were determined. The activation energy for BOR was found to be 13.6 kJ mol−1 and 15.3 kJ mol−1 for MIL-101_Au@NH2 and MOF-808_Au@NH2, respectively. The number of transferred electrons, n, was found to be 7.0 and 3.1 for MIL-101_Au@NH2 and MOF-808_Au@NH2, respectively. This study demonstrates that MOF-based electrocatalysts can enhance DBFCs' performance, while offering insight into the potential usage of MOFs in other fuel cell technologies.

[1] B. Šljukić, D.M.F. Santos, "Direct borohydride fuel cells", in: "Direct Liquid Fuel Cells: Fundamentals, Advances, and Future", 1st ed., R.G. Akay, A.B. Yurtcan (eds.), Academic Press, USA, 203-232 (2021)

[2] G. Backovic, B. Šljukić, G.S. Kanberoglu, M. Yurderi, A. Bulut, M. Zahmakiran, D.M.F. Santos, Ruthenium (0) nanoparticles stabilized by the metal-organic framework as an efficient electrocatalyst for borohydride oxidation reaction, International Journal of Hydrogen Energy, 45, 27056-27066 (2020).
Ru-Loaded Highly Graphitized Porous Carbon with High Pyrrolic-N Content for Superb Electrochemical Hydrogen Evolution
Authors: Yu Jong-Sung , Shin Cheol-Hwan , Yu Jeong-Hoon
Published: February 2024

The performance of electrocatalysts is closely related to their supporting materials since their properties such as heteroatom doping, porosity, graphiticity, and electrical conductivity play a decisive role on catalyst performance. We report here the preparation of N-doped highly graphitized porous network-structured carbon (N-HGC) as a catalyst support for Ru nanoparticles (NPs) catalytically active for hydrogen evolution reaction (HER) using simple pyrolysis of g-C3N4 in the presence of Mg metal. The as-prepared N-HGC shows high graphiticity confirmed by XRD and Raman analyses, high electrical conductivity, and large surface area along with large amount of open mesopores, containing the proper amount of N doping rich with high pyrrolic-N content for homogeneous distribution of Ru NPs. This Ru/N-HGC catalyst shows a remarkably low overpotential of 9.6 mV (vs RHE) at 10 mA/cm2, which is near ideal and far better than state-of-the-art Pt/C. It also illustrates superb stability, maintaining the HER activity for 200 h and 10k CV cycles without any significant degradation. This superb HER performance is attributed to the robust N-HGC support featuring thin carbon structure, high electrical conductivity, suitable porosity, and N pyrrolic doping. The atomistic basis for the low overpotential is explained via Grand Canonical Quantum Mechanics (GC-QM) calculations. These calculations show that the pyrrolic-N in the support strengthens the coupling to Ru NP and weakens the binding of H to Ru NP, improving the rate determining Tafel reaction.
Fabrication of Faceted Metal Nanocrystal Electrodes By Solid-State Dewetting
Authors: Sharma Rakesh Kumar , Harsha Shreyas , Mul Guido , Altomare Marco
Published: February 2024

Electrochemical reactions are electrode-structure sensitive and hence microstructural properties of the (electro)-catalysts such as size, shape, exposed facets, and grain boundaries, among others, strongly affect the activity, selectivity, and stability.1, 2 Conventional methods based mainly on wet-chemistry have been widely adopted to synthesize nanocrystal (NC) electrocatalysts, and proved suitable to control their features. However, these methods require several synthesis steps, which increase the production time and complexity, and resulting particles often feature a complex composition (due to impurities such as ligands or templating agents) and suffer from durability issues, due e.g. to particle detachment from the substrates.

We explore solid-state dewetting (SSD) as an alternative way to produce metal nanocrystal electrocatalysts while overcoming various challenges intrinsic of conventional approaches.3, 4 Dewetting is the heat induced agglomeration of thin metal films into particles. Taking Pt as a case study, we have investigated the effect of various SSD parameters such as metal film thickness, substrate crystallographic features, and dewetting conditions (time/temperature/atmosphere) on the physicochemical properties of the resulting dewetted metal NCs. Under optimized conditions, dewetting forms monodispersed faceted Pt nanocrystals of tunable size. Low- or high-index facets can be designed (as shown in the figure below) by tuning the substrate orientation and dewetting conditions (e.g., T, dewetting gas). In general, dewetted Pt NCs show higher (ESCA-normalized) activity towards hydrogen evolution reaction (HER) compared to Pt thin films, and their mass activity is comparable to the state-of-the-art Pt/C. The talk will delve into correlations between microstructure (grain size, shape and facets etc.) and the electrochemical performance of dewetted NCs.

From a general point of view, dewetted NCs show intriguing electrochemical and mechanical properties, and hence dewetting appears to be a promising approach for preparing active and robust nanostructured (electro)-catalysts for various applications. In ongoing work, we investigate dewetting to deposit catalysts on gas diffusion layer (GDL) electrodes and test their performance in PEM lab-scale electrolyzers.

Figure 1
Initial Degradation Issues in AEMWE and the Importance of Catalyst/Ionomer Binding
Authors: Hyun Jonghyun , Kim Hee-Tak
Published: February 2024

With the recent development of highly alkaline stable anion exchange membranes (AEMs) and ionomers (AEIs), anion exchange membrane water electrolyzer (AEMWE) has garnered attention due to its ability to achieve high hydrogen production rate at a low cost. The performance of AEMWE is determined by the anode catalyst layer, which can be made up of either a mixture of metal nanoparticles and polymer binders or a single metal. Although the integral metal has high mechanical properties, its performance is limited due to low electrochemical surface area and difficulties in mixing with binders, which makes it unsuitable for use in pure water. Catalyst layers made up of a combination of metal nanoparticles and polymeric binders can achieve high performance with a large surface area, but they often have low durability due to detachment of the anode catalyst layer from the porous transport layer substrate during water electrolysis. To prevent this, the anode catalyst layer must have high physical stiffness and it can be achieved by the strong bonding between the metal nanoparticles and the ionomer binder. This presentation investigates the phenomenon of initial performance degradation in AEMWE with an anode catalyst layer composed of metal nanoparticles, highlights the significance of the physical stiffness of the anode catalyst layer, and proposes that the issue can be resolved by introducing a polymer binder with high adhesion between the metal nanoparticles and the ionomer binder.
Materials Integration and Catalyst Interfaces in Anion Exchange Membrane, Low Temperature Electrolysis
Authors: Alia Shaun M , Kreider Melissa , Volk Emily K. , Chan Ai-Lin , Clauser Arielle L , Sugar Josh D
Published: February 2024

As an energy carrier, hydrogen has unique advantages due to its high energy density, ability for long-term storage, and the ability to convert between chemical bonds and electricity. [1] Although hydrogen currently has a small role in energy pathways, low-cost renewable power sources can allow for significant growth. Anion exchange membrane (AEM) electrolyzers leverage several advantages, including a zero-gap approach that typically improves upon the efficiency of traditional alkaline systems. [2] Compared to proton exchange membrane (PEM) electrolyzers, the high pH also allows for platinum group metal-free (PGM-free) catalysts and component coatings (transport layers, separators) that can reduce system cost and improve long-term durability. In recent years, membrane advancements have further enabled higher AEM performance, particularly in supporting electrolytes. [3]

This presentation includes an overview of efforts in AEM electrolysis and focuses on materials choices and their integration. While components are readily available that can achieve high performance, individual properties and their interactions create integration challenges. [4] In catalyst and transport layers, large particle sizes and lower catalyst conductivity coupled with the high distance between transport layer fibers can lead to lower catalyst utilization and high catalyst layer resistances. The ionomer, while critical for ionic transport in water, is primarily needed in supporting electrolytes for structural integrity, and changes to the ionomer content, type, and its distribution throughout the catalyst layer have been explored for its effect on performance and durability. These experiments demonstrate the complications of developing a single set of materials and test protocols for component evaluations.

References

[1] B. Pivovar, N. Rustagi, S. Satyapal, The Electrochemical Society Interface
2018, 27, 47.

[2] S. Alia, D. Ding, A. McDaniel, F.M. Toma, H.N. Dinh, Chalkboard 2-how to make clean hydrogen. The Electrochemical Society Interface
2021,
30 (4), 49.

[3] S. M. Alia, HydroGEN: Low Temperature Electrolysis, https://www.hydrogen.energy.gov/pdfs/review21/p148a_alia_2021_p.pdf 2021.

[4] H. Dinh, HydroGEN Overview: A Consortium on Advanced Water Splitting Materials, https://www.hydrogen.energy.gov/pdfs/review22/p148_dinh_2022_o.pdf 2022.
The Power of Reference Electrodes in AEM Electrolysis
Authors: Guruprasad Naveen , de Groot Thijs Theodorus , van der Schaaf John
Published: February 2024

The use of reference electrodes is a powerful diagnostic tool to determine the overpotentials associated with oxygen and hydrogen evolution reaction. Yet, the use of reference electrodes in flow cells is still uncommon and provides several challenges especially related to the stability of the potential of the reference electrode. This study investigates the use of a reference electrode in a well-performing iridium-free AEM flow cell with a cell potential of <1.8 V @ 1.5 A cm-2. The reference electrode consists of electrically insulating foil with two platinum wire electrodes on one side as shown in Figure 1(left). A small micro-current is passed through the platinum wires to maintain hydrogen coverage on the reference electrode to establish equilibrium cell potential. The use of the reference electrode shows that the platinum-ruthenium cathode performs particularly well with an overpotential of <0.1 V @ 0.2 A cm-2.

The reference electrode also is useful for the study of cell degradation. One of the major challenges of coupling electrolyzer directly to renewables are reverse currents flowing after shutdown in alkaline and AEM electrolyzers [1]. In this study, polarities were reversed to simulate these reverse currents. This lead to a significant increase in cell potential. It is clearly evident from Figure 1(right) that the cathode overpotentials increased significantly after this reverse current application, thereby indicating that the platinum-ruthenium cathode is vulnerable to reverse currents.

[1]Ashraf Haleem et al, Effects of operation and shutdown parameters and electrode materials on the reverse current phenomenon in alkaline water analyzers, Journal of Power Sources, Volume 535, 2022, 231454, ISSN 0378-7753, https://doi.org/10.1016/j.jpowsour.2022.231454

Figure 1
OER Activity of Iridium Nanoparticle Catalysts By RDE and Comparison with MEAs
Authors: Ioroi Tsutomu , Nagai Tsukasa , Siroma Zyun , Yasuda Kazuaki
Published: February 2024

To accelerate the deployment of green hydrogen, lowering the cost of water electrolyzer is one of the important issues. Iridium anode catalyst is a key material for highly efficient and stable operation of proton exchange membrane (PEM) water electrolyzer, however, limited resources of iridium lead to higher cost and the limited availability. Therefore, there is a strong need to develop novel catalysts that can reduce iridium usage without compromising on activity. Rotating electrode half-cell is a useful technique for OER activity measurement of anode catalysts [1], however broader consensus about the activity measurement protocol is still missing. In addition, it is also unclear whether the measured activity values from the RDE are consistent with those of the MEA. The RDE activity is influenced by various measurement parameters; catalyst loading on the disk electrode, ionomer content, electrolyte conductivity, potential range etc. Here, we demonstrate the impact of these RDE parameters on the measured OER activity using various iridium catalysts [2]. The OER activity was evaluated by linear sweep voltammogram at a scan rate of 1 mV sec-1 and a disk rotation rate of 3,600 rpm to minimize the contribution of capacitive current and mass transfer loss due to O2 bubbles. Too much catalyst loading on the disk electrode leads to a decrease in apparent OER activity, so that catalyst loading should be in the range where the catalyst activity is independent of the loading amount. Electrolyte solution was also found to have a significant effect on OER activity; comparing to the activity in perchloric acid solution (0.1 M HClO4), sulfuric acid solution (0.05 M H2SO4) and phosphoric acid (0.1 M H3PO4) showed 60% and 40% activity, respectively. To verify the obtained values of OER activity by RDE at the optimized condition, the OER activities were also determined by MEAs at corresponding conditions. The OER activities of MEA and RDE were found to be approximately the same regardless of catalyst species. Detailed measurement conditions and results will be discussed at the Meeting.

References

S. M. Alia, G. C. Anderson, J. Electrochem. Soc., 166 (2019) F282.

T. Ioroi, T. Nagai, Z. Siroma, K. Yasuda, Int. J. Hydrogen Energy, 47 (2022) 38506.
Regulating the Electronic Structure of IrO
x
/SnO
y
with NaCl for Efficient Proton Exchange Membrane Water Electrolysis
Authors: Kim Sol , Woo Jinwoo , Ngo Yen-Linh Thi , Jang Jong Hyun , Seo Bora
Published: February 2024

Hydrogen has been considered as a promising energy carrier because of its high gravimetric energy density. However, most hydrogen has been produced by steam methane reforming, which releases significant amounts of CO2 during the process. In contrast, water electrolysis (WE) offers the most sustainable way to produce hydrogen without carbon emissions. Especially, proton exchange membrane water electrolysis (PEMWE) technique has attracted much attention due to its high efficiency, compact design, and fast response to load fluctuations, enabling the integration of renewable energy. However, the inevitable use of precious metal (Ir, Ru) catalyst due to the sluggish kinetics of oxygen evolution reaction (OER) has hindered the practical implementation of PEMWE. In this regard, developing low-content Ir-based catalysts with high activity is critical for enhancing the cost efficiency of PEMWE. This presentation will propose a synthesis strategy for tin oxide-supported iridium oxide (IrO
x
/SnO
y
_NaCl) catalyst prepared using NaCl as a sacrificial template. This approach allows uniform dispersion of Ir particles and regulation of its valence states to favor the OER. The synthesized IrO
x
/SnO
y
_NaCl catalyst exhibited high OER activity and mass activity comparable to the state-of-the-art Ir-based OER catalysts. Electrochemical and X-ray spectroscopic analyses demonstrated that the use of NaCl template can improve the catalytic activity of IrO
x
by tuning the valence state ratio (Ir3+/Ir4+). Moreover, IrO
x
/SnO
y
_NaCl catalyst showed a high single-cell performance of PEMWE, achieving mass activity 2.6 times higher than commercial IrO2.
(Invited) Fundamental Structure-Function Relationships for Iridium Oxide Catalysts in PEM Water Electrolyzers
Authors: Zenyuk Iryna , Wang Cliffton , Morimoto Yu , Cheng Lei
Published: February 2024

The intermittency of renewable energy poses significant challenges to developing a grid system that utilizes primarily renewable-based sources. Proton exchange membrane water electrolyzers (PEMWEs) can convert surplus energy from the grid into chemical energy in the form of green hydrogen, which can then be used to generate electricity when the renewable supply is low. Despite much technological advancement over the last two decades, PEMWEs still face many barriers to widespread commercialization. Around a quarter of the cost of the PEMWE system is attributed to iridium, a highly scarce material used as the oxygen evolution reaction (OER) catalyst on the anode side. To enable lower loadings/higher utilization of these catalysts, fundamental studies on iridium activity and degradation are necessary. As it stands in the literature, studies on how physical properties of the catalyst (i.e. crystallinities, valance states, etc.) affect PEMWE performance are scarce. This work aims to elucidate the relationship between structural properties and efficiency/performance for iridium oxide (IrOx ) catalysts in PEMWEs. Five commercially available iridium oxide catalysts were characterized (47491 Alfa Aesar, TEC77100, TEC77110, FIO-01, FIO-11) using transmission electron microscopy (TEM), scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) analysis, and x-ray diffraction (XRD) to obtain crystallinities, particle size distributions, specific surface areas, thermal stabilities, elemental compositions, and valance states. Afterwards, kinetic performance was baselined by taking cyclic voltammograms (CVs) via rotating disk electrode (RDE) experiments and electrochemical surface areas (ECSA) were approximated by using a novel analysis developed in this work that can relate the hysteresis in OER potentials to a double layer capacity. Results show that greater amorphous character of IrOx was correlated with increased kinetic performance at the expense of electrochemical stability across redox potentials between 0-1.6V. From the cyclic voltammograms, the catalyst with the most amorphous character underwent multiple (two, possible three) redox transitions, while the one with the most crystalline character showed no evidence of any redox transitions. It was also found that increased ECSA was correlated with greater physical surface areas obtained from BET analysis and that greater amorphous character resulted in a higher Ir III :Ir IV ratio. For future work, we aim to incorporate these fundamental structure-function insights to create standardized accelerated stress tests for PEMWEs, as standards for durability testing have yet to be established.
Iridium Single Atom Catalysts for Oxygen Evolution Reaction in Acidic Medium
Authors: Rouger Jean , Cavaliere Sara , Jaouen Frederic , Jones Deborah J. , Dufour Fabien , Georges Maureen , Thuilliez Julien
Published: February 2024

In order to reduce CO2 emissions and produce clean hydrogen one solution is to use sustainable energies (wind, solar or hydraulic) coupled with water electrolyser to produce H2 and store it before use it in fuel cell. The electrolyzer based on proton exchange membranes (PEM) is a promising technology because it can reach high current density (2 A.cm-2) [1] and can be easily coupled with intermittent energy sources [2]. However, the acidic conditions and working temperatures (80 °C) require the use of noble metals. On the anode side the oxidative condition prevents the use of carbon supported catalyst and the best catalyst for the oxygen evolution reaction (OER) so far is IrOx.

The use of Ir single atom catalyst (SAC) supported on conducting oxide is a promising way to reduce the quantity of the scarce and expensive noble metal, increasing the electroactive surface and durability. SACs present an excellent dispersion and activity [3] and some conducting oxides are very promising regarding electrical conductivity and stability under oxidative conditions [4]. There are different approaches to prepare Ir SAC (wet impregnation, co-precipitation, photoelectrochemical reduction...) [3], whose success mainly depends on the nature of the Ir precursor, its interaction with the support and the thermal treatment temperature/duration. Some research groups have prepared and characterized Ir SAC on indium-tin oxide [5] but the activity and stability still need to be improved.

The objective of this communication is to present the synthesis and the characterization of IrSAC on different conducting oxide supports. Ir precursor was synthesized and deposed on various supports. The physical characterization entails XRD, TEM, MEB, EDX to assess the morphology and composition of the catalyst. Spectroscopic analysis like XPS and XAS brings information on the chemical environment of Ir sites, while electrochemical measurements give information on the OER activity and stability of the catalyst.

References

[1] C.D. Ferreira da Silva et al., ACS Catal., 2021, 11, 4107-4116

[2] O. Schmidt et al., Int. J. Hydrog. Energy, 2017, 42, 30471-30492

[3] J. Liu, ACS Catal., 2017, 7, 34-59

[4] Moriau et al., ChemCatChem, 2022, 14, e202200586

[5] D. Lebedev et al., ACS Cent. Sci.
2020, 6, 1189-1198

[6] Q. Wang et al., ACS Catal.,
2020
, 142, 7425-7433
TiNxOy/TiN Supported Ir-Oxide/Ir As Efficient OER Electrocatalyst for Acidic Water Electrolysis
Authors: Sharma Raghunandan , Karade Swapnil S. , Andersen Shuang Ma
Published: February 2024

Increasing the mass activity of Iridium-based electrocatalysts for oxygen evolution reaction (OER) is of significant importance for sustainable acidic water electrolyzers generating green hydrogen. Here, we have studied surface oxidized TiN (TiNxOy/TiN) as a catalyst support for Ir-based OER electrocatalysts with high mass activity. TiNxOy/TiN supported Ir-oxide/Ir nanoparticles were synthesized using a microwave-assisted approach. The synthesized IrO2@Ir/TiN with an Ir loading of 40 wt% exhibits a mass-normalized OER activity of ~2.4 times that of a commercial benchmark IrO2 OER electrocatalyst. The synthesized TiNxOy/TiN supported Ir-oxide/Ir catalyst, owing to superior utilization of the active catalyst surface and improved intrinsic activity through catalyst-support interaction, enables significant (~60 wt.%) reduction in the Ir metal loading required to obtain equivalent OER performance, compared to commercial benchmark. In addition, accelerated stress test (AST) involving potential cycling in acidic media suggest the IrO2@Ir/TiN catalyst to be of relatively higher durability (activity retention: 79%) compared to that of the commercial equivalent (activity retention: 66%). In the presentation, we discuss the findings focusing on impacts of surface chemistry of the synthesized catalysts on their mass-activity and the degradation mechanisms during AST. The study opens a new perspective for further research towards development of low-Ir loading OER electrocatalysts.

Reference

Karade, S. S.; Sharma, R.; Gyergyek, S.; Morgen, P.; Andersen, S. M., ChemCatChem 2023, e202201470, DOI: https://doi.org/10.1002/cctc.202201470.
Characterizing the Dynamic Response and Start-up Process of the Electrolyzer for Operation Optimization in Renewable Energy Applications
Authors: Shangguan Zixuan , Zhang Cunman
Published: February 2024

The current water electrolyzer industry is experiencing rapid growth due to the increasing demand for renewable hydrogen as a clean energy. The application in renewable energy demands the dynamic operation of the electrolyzer, while the dynamic and start-up response of the electrolyzer is not comprehensively studied. This study focuses on characterizing the dynamic response, as well as the start-up process of electrolyzers. The dynamic response of the electrolyzer is analyzed using an alternating input current step, and the electrochemical response is correlated with the dynamic control of the electrolyzer. The overshoot voltage during the alternation process is taken as the indicative response under different baseline current, current change amplitude and frequency. The start-up process of the electrolyzer is also explored and analyzed with respect to the start-up time, energy cost, and the initial status of the electrolyzer as well as the liquid circulation rate. The overall energy cost, as well as the start-up time, across the start-up process possesses a strong linear relationship towards the initial temperature of the start-up. Besides, the liquid circulation rate has an impact on start-up power, because higher circulation rate brings more uniform temperature distribution of the electrolyzer. Tuning the liquid circulation rate can help to reduce the elapsed time, and hence accelerate the response speed. The findings provide a framework for testing the electrolyzer and optimizing the start-up process. This paper offers valuable insights that can be applied in the development and design of large-scale electrolyzers, thereby ensuring more efficient and sustainable production of hydrogen. Overall, this paper constitutes an important contribution to the study of electrolyzer and has the potential to shape future research in the area of electrolyzer development and operation optimization.

Figure 1
Analysing the Degradation Phenomena of a Commercial Proton Exchange Membrane Water Electrolyzers
Authors: Kimmel Benjamin , Morawietz Tobias , Biswas Indro , Gazdzicki Pawel , Gago Aldo , Friedrich K. Andreas
Published: February 2024

Decarbonization of our energy system has become a priority to mitigate climate change. Therefore, the use of renewable energies is mandatory which also requires a long-term storage possibility. Proton exchange membrane water electrolyzers (PEMWE) are ideal for producing green hydrogen for transport, industry and heat. Important advantages are their compactness and high flexibility to operate under dynamical conditions. To be competitive it is necessary on the one hand to reduce the investment costs and on the other hand to ensure a long life of electrolyzers to limit operational expenses. Industry often faces the problem that the operating histories of their stacks are unknown when they are operated by customers. Nevertheless, understanding of the degradation mechanisms is of great importance to develop new components with reduced cost and enhanced durability. Here we analyse the cell components of a commercial PEMWE stack, which has been operated by a customer for long periods of time under unknown conditions, with the help of electrochemical and physical methods. Samples of the operated components were cut at specific locations and characterized in a 4 cm2 single cells. The aged components were successively replaced by new ones or regenerated to isolate and quantify the contribution of individual components on performance losses. This way, we have identified the catalyst coated membrane (CCM) as the component strongest affected by degradation. By using X-ray photoelectron spectroscopy (XPS) we identified different types of contamination like Pb and Fe. Remarkably, they were found on aged and unused components which is an indication for impurities due to the production process. In addition, energy dispersive X-ray spectroscopy (EDS) analysis showed Ca traces which is characteristic of CCM contamination when insufficiently deionized water is used for cleaning cell components, in particular the Ti porous transport layers (PTL). The CCM notably degrades by defects of the catalytic layer, due to contaminations and ionomer rearrangement. Signs of erosion were observed on the cathodic side of the Bipolar Plate (BBP) by means of SEM and atomic force microscopy (AFM), while the electronic conductivity remained unchanged. In contrast a pronounced oxidation concurrent with reduced conductivity is measured for the BPP on the anode side. The combination of electrochemical characterization with stepwise regeneration processes and physical ex situ analysis allows to draw conclusions about the impact of different components on degradation and to analyse the underlying aging mechanism occurring in each component.
Advancing Fundamental Understanding of Electrolyzers for Cost-Effective Green H2 Production
Authors: Dubouis Nicolas
Published: February 2024

Reaching net-zero by 2050 is critical to limit global warming to below 2°C by 2100. Renewable energy will play a vital role in this transition, and one of the key challenges is to deploy them at a multi-GW scale. TotalEnergies’ Hydrogen R&D department is committed to developing green H2 production and storage technologies to meet this challenge.

In this talk, we will focus on alkaline electrolysis, which has been around for over a century but still presents significant challenges for GW-scale projects. We will discuss how our research can improve the efficiency, durability, and cost-effectiveness of alkaline electrolyzers. For instance, we will demonstrate using a simplified electrolyzer model that a good understanding of the kinetics of ageing phenomena can drastically impact the H2 production cost and the maintenance philosophy of an industrial plant. Based on these observations, we will propose a methodology to refine this understanding, and to better grasp the effect of intermittent operation of the electrolyzer on its ageing. Finally, we will highlight some fundamental findings made by academia that we believe could be good to explore to increase alkaline electrolyzer performance.

In conclusion, there is a need to increase the dialogue between industry and academia to tackle the challenges of green H2 production at the multi-GW scale. By working together, industry and academia can develop more efficient and cost-effective green H2 production technologies, bringing us closer to achieving our ambitious multi-GW scale targets.