bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) In Situ Electrochemical TEM and XAS Studies in Oxygen Evolution Reaction
Authors: Balaghi S. Esmael , Sologubenko Alla S. , Najafpour Mohammad Mahdi , Patzke Greta Ricarda
Published: May 2020

The design of a highly efficient, cost-friendly and the green water oxidation catalyst is one of the most challenging research areas in the field of sustainable energy. Despite the presence of promising research findings of active catalysts in OER, their stability during long-term water oxidation reactions remains unexplored. The almost infinite number of possible compositions of mixed oxides makes the latter a great challenge towards the improvement of the stability and activity of such OER catalysts for future applications in water splitting devices and batteries.[1] Modern advances in the fabrication of micro electrochemical cells for operando microscopy have opened new horizons to perform the real-time investigation of electrochemical dynamic behaviors at the electrode-electrolyte interface.[2,3]

In this study, an in situ electrochemical TEM approach was employed to directly visualize the early stages of OER and screening the morphological evolution of catalyst on the working electrode surface. The aforementioned method was applied on La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), La0.8Sr0.2MnO3 (LSM) and LiNi0.33Mn0.33Co0.33O2 (LNMC) mixed oxides, respectively. Furthermore, electron atomic pair distribution function (ePDF) was used in order to obtain the quantitative insight into the structural changes of the electrode surface under operational conditions. The electrochemical stability and structural changes behavior of the catalysts during OER was studied using in situ electrochemical X-ray absorption spectroscopy (XAS). Moreover, this structural changing process was reinvestigated by several ex situ methods such as X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (PXRD), Raman spectroscopy, transmission electron microscopy, (TEM), scanning electron microscopy (SEM), cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). Finally, we propose a novel mechanistic insight, which demonstrates that the ongoing quest for true catalysts design in OER is a dynamic and rapidly developing research area.

References:

[1] W. T. Hong, M. Risch, K. A. Stoerzinger, A. Grimaud, J. Suntivich, Y. Shao-Horn, Energy Environ.
Sci.
2015, 8, 1404.

[2] T. Li, O. Kasian, S. Cherevko, S. Zhang, S. Geiger, C. Scheu, P. Felfer, D. Raabe, B. Gault, K. J. J. Mayrhofer, Nat. Catal.
2018, 1, 300.

[3] Y. He, X. Ren, Y. Xu, M. H. Engelhard, X. Li, J. Xiao, J. Liu, J.-G. Zhang, W. Xu, C. Wang, Nat.
Nanotechnol.
2019, 14, 1042.
Synthesis and Characterization of Composite MoSe2-MoO2 By Hydrothermal and Their Electrocatalytic Performance for Hydrogen Evolution Reaction
Authors: Tran Thai XUAN , Mohamed Siaj
Published: May 2020

For more energy-efficient and economical hydrogen production, highly active noble metal-free hydrogen evolution catalysts are a priority for all. Herein we report a facile hydrothermal synthesis of composite MoSe2-MoO2. The surface morphology and chemical composition of the synthesized materials were investigated by SEM, TEM, Raman spectroscopy, XPS and XRD. After characterizations, the materials were directly used as an electrode to evaluate their HER performance. A comparison between pure MoSe2, pure MoO2 and MoSe2-MoO2 nanosphere shows that the porous MoSe2-MoO2 nanosphere exhibits higher catalytic activity for electrocatalytic hydrogen evolution reaction (HER)(figure 1). Based on our data, it can be concluded that the porous structure material could improve the surface active area which yields higher HER catalytic activity. The present study provides a simple and effective way for the exploration of efficient Mo-based HER catalysts.

Figure 1
Surface Modification of Rutile TiO2 with Metal Chalcogenides for Hydrogen Evolution
Authors: Nolan Michael , Niemitz Lorenzo , Rhatigan Stephen
Published: May 2020

The hydrogen evolution reaction (HER) is a key reaction in water splitting and there is an intensive search for suitable HER catalysts that will promote this reaction and also show good stability, while not using precious metals. We have studied the surface modification of rutile TiO2 with metal chalcogenide nanoclusters for the promotion of the hydrogen evolution reaction (HER) using density functional theory corrected for on-site Coulomb interactions (DFT+U).

Recently, metal chalcogenides have emerged as potential catalysts for the HER due to the favourable interaction of H at chalcogen sites, particularly those that are undercoordinated. In developing materials for HER the key descriptor has been the adsorption energy of hydrogen at the catalysts, with the target free energy being close to 0 eV. Analogous to noble metal loading, surface modification of TiO2 with nanoclusters of potential HER co-catalysts, based on earth-abundant materials, is an emerging strategy. This approach combines the desirable properties of a stable titania photocatalyst with active sites provided by the low-coordinated chalcogen ions of the supported clusters.

Our models consist of M4X4 (M = Sn, Zn; X = S, Se) nanoclusters at the rutile (110) surface and we examine the Gibb’s free energy of H adsorption at the modified surface which is a useful material descriptor in assessing the performance of a HER catalyst. These calculations take into account changes in the entropy and the zero-point energies (ZPEs) of the reactants and products, which our results show are material specific. As expected, the interaction of H is more favourable at the titania surface and forms stable hydroxyls. However, after subsequent adsorption events the surface sites become saturated and H adsorption at chalcogen sites exhibit Gibb’s free energies in the active range, particularly for MS modifiers relative to MSe.
Ir Decorated Fractal Ni Catalysts for the Oxygen Evolution Reaction
Authors: Hao Minghui , Gaudet Julie , Guay Daniel
Published: May 2020

Porous and fractal Ni electrode synthesized by the Dynamic Hydrogen Bubbling Template (DHBT) method (Ni DHBT electrode) have shown very promising performances for the oxygen evolution reaction (OER) in alkaline electrolyte. This was thought to arise as a result of the extended electrochemical active surface area and its superaerophilic properties that facilitates the release of oxygen bubbles[1]. Herein, we report on a method to decorate the Ni DHBT electrode with Ir atoms via a galvanic replacement (GR) reaction. The resulting electrode has very low loadings of Ir (0.26 atom % as determined by EDX). As shown in Figure 1, micrometer-sized pores are observed at the surface of deposits, with pore walls exhibiting a highly porous cauliflower-like secondary structure, with much smaller pore diameter (typically less than 500 nm). The structure seen in Figure 1 was observed over the entire 0.32 cm2 geometric surface area of the deposits. The morphology of the Ir-modified electrode is not changed with respect to Ni DHBT electrode, indicating that the GR reaction is occurring only at the surface of the deposit. Voltammetry cyclic tests in 1M KOH solution showed hydrogen adsorption/desorption (Hupd) peaks of Ir as well as the redox peaks of Ni(OH)2 which suggested the coexistence of Ir and Ni content at electrode/electrolyte interface. The activity for the OER of Ni DHBT electrode was further improved by decoration with Ir, resulting in an overpotential of 195mV at 10 mA/cm2 and a Tafel slope of 46 mV/dec. To the best of our acknowledgment, this is one of the best performing Ni based OER catalysts reported so far. The interaction of oxygen bubbles with the electrode surface will also be assessed using both optical imaging and acoustic emission characterization.

[1] M. Hao et al., “Hydrogen Bubble Templating of Fractal Ni Catalysts for Water Oxidation in Alkaline Media,” ACS Appl. Energy Mater., vol. 2, no. 8, pp. 5734–5743, Aug. 2019.

Figure 1
Towards Selective Partial Water Oxidation to Form H2O2: An Attractive Substitute for O2 Evolution in Water Splitting
Authors: Mei Bastian Timo , Wenderich Kasper , Nieuweweme Birgit , Mul Guido
Published: May 2020

Efficient and financially attractive (photo)electrochemical water splitting for the production of hydrogen (H2) is essential to drive a green hydrogen economy. However, techno-economic analysis predicts that the price of H2 obtained through (P)EC water splitting is over $10 000 ton-1 at solar-to-hydrogen (STH) efficiencies of ca. 10 %, whereas the current market value of H2 produced by conventional steam methane reforming is only $1400 ton-1.[1, 2] Co-production of high-value chemicals at the anode is an appealing strategy to increase the financial attractiveness of the production of 'green hydrogen.

In ‘classic’ (P)EC water splitting, oxygen is the main product at the anode, formed at a potential of E0 (O2/H2O) = +1.23 V vs RHE. Though thermodynamically less favorable (E0 (H2O2/H2O) = +1.78 V vs RHE), the selective partial oxidation of water to hydrogen peroxide (H2O2) is of industrial interest.[2] With a market price of $500-1200 ton-1 for H2O2 and given the low market value of O2 (only $35 ton-1), the financial incentive is clearly demonstrated. Considering that the demand for H2O2 is constantly increasing, hydrogen production through a process with concomitant H2O2 has a high potential of becoming competitive with steam methane reforming.

Here, we discuss the techno-economics of a PEC water splitting system producing H2O2 and H2. We will clearly show that an electrochemical process holds great financial promise for industrial development. Not only do we demonstrate at which prices H2 and H2O2 can be sold to make a profit, we also discuss which parameters need to be optimized to decrease the hydrogen price. Interestingly, when the H2O2 price is $0.85 kg-1, an STH of only 9.39% is required to compete with hydrogen production by steam methane reforming.

As the anodic formation of H2O2 is not yet well explored, it will also be shown that continuous electrochemically production of H2O2 at a rate of 0.092 µmol min-1 cm-2 @ 7.08 mA/cm2 through partial water oxidation can easily be achieved in an non-optimized electrochemical cell. Finally, the importance of electrolyte, electrode and reactor engineering to increase the Faradaic efficiency and the rate of H2O2 production will be revealed.

References

1. Shaner, M. R.; Atwater, H. A.; Lewis, N. S.; McFarland, E. W. A Comparative Technoeconomic Analysis of Renewable Hydrogen Production using Solar Energy. Energy Environ. Sci., 2016, 9, 2354-2371.

2. Mei, B.; Mul, G.; Seger, B. Beyond Water Splitting: Efficiencies of Photo-Electrochemical Devices Producing Hydrogen and Valuable Oxidation Products. Adv. Sustainable Syst. 2017, 1, 1600035.
The Controlled Preparation of Ordered Iridium Oxide Nanotubes Arrays for Oxygen Evolution Reaction
Authors: Lu Zhuoxin , Shi Yan , Wang Zhida , Guo Changqing , Tan Hongyi , Yan Changfeng
Published: May 2020

Ordered electrode is believed to be the next generation of MEA. One-dimensional-arrays material possesses high surface area, oriented electron transfer pathway and facile mass transfer pathway, which shows great potential as electrocatalyst. For OER electrode, IrO2 is still the irreplacable choice at present status. To construct IrOx based nanotube/nanowire arrays could increase the performance of OER electrode with reduced loading amount of Iridium. Titanium oxide nanotube arrays (TNTA) is a promising candidate for the preparation of 1-D arrays electrode as its prominent stability, ordered structure and sufficient conductivity with simple modification. In order to achieve the open-end nanotube structure for the fully utilization of noble metal catalyst, controlled electrochemical deposition is applied.

In our previous work, IrOx nanotube arrays performs similar current density with 1/20 loading amount of commercial IrO2 nanoparticle at the same potential. To achieve the length control of IrOx nanotube arrays, the electrodeposition of IrOx on TNTA with cyclic voltametry method was studied. By altering the scan rate, continuous IrOx nanotube arrays with different length ranged from 500 nm to 1400 nm was achieved. This phenomenon may probably due to that the deposition in the tube is diffusion controlled, while the deposition at the mouth of TNTA keeps constant due to sufficient supplement of precursor form the bulk electrolyte. In a single cycle, as the depositing goes on, the concentration gradient along the tube forms and results in uneven deposition. Different scan rate results in different duration of depositing in a single cycle. And longer duration means more uneven deposition, and leads to shorter nanotube.

At present, to obtain IrOx nanotube arrays with uniform tube wall, control deposition with pulsed potential deposition method is studied. By altering the relaxation and deposition time, IrOx with uniform thickness and tunable length can be achieved. And the thickness of IrOx tube wall can be controlled, too. By achieving uniform and thinner tube wall, the utilization rate of Iridium can be further increased.
(Invited) Engineering Nanoporous Iridium Microstructures for Stable Oxygen Evolution Electrocatalysis in Acid Media
Authors: Chatterjee Swarnendu , Snyder Joshua David
Published: May 2020

Water splitting through PEM electrolysis provides promising route for renewable energy storage and production of high purity hydrogen and oxygen gases. Iridium oxide which is the only stable metal oxide that can evolve oxygen at the anode with reasonable activity is typically alloyed with less expensive transition metals to make high surface area Ir alloy nanostructures for commercially viable oxygen evolution reaction (OER) electrocatalysts. The chemical and morphological stability of such alloy nanostructures at anodic potential in acid is still a major concern for long term electrolysis. Here, we show dealloying as an appropriate method to synthesize free standing high surface area, oxide skinned nanoporous bimetallic Ir (np-Ir) alloys for efficient and stable OER electrolysis in acid media. The metallic core and absence of any binder/support result in low electrode and charge transfer resistance; ultimately giving rise to lower overpotential and much improved ECSA (electrochemically active surface area) normalized current densities compared to traditional IrO2 electrocatalysts for acidic OER. We also demonstrate with a proper acid concentration in the dealloying electrolyte and a requisite atomic fraction of iridium in the precursor alloy, dealloying gives rise to nanoporous microsheets of core shell Ni-Ir alloy. Compared to the IrO2 nanoparticles, the nanoporous Ir microstructures offer high carrier mobility because of the interconnected ligamentous structure that provides easy supply of electrons on the iridium oxide surface required to break the water molecule. Overall, the nanoporous Ir obtained through dealloying exhibits low overpotential and stable OER electrolysis in acid media.
First Principles Modelling of Surface Modified TiO2 for Water Activation and Oxygen Evolution
Authors: Nolan Michael , Rhatigan Stephen
Published: May 2020

The photocatalytic oxidation of water to molecular oxygen is a key step in the water splitting reaction. The development of robust catalysts with high efficiency in this half-reaction is crucial for achieving technological application of water splitting. Density Functional Theory simulations can provide key insights into potential catalysts for this reaction. In this contribution we describe our work on modelling of surface modified TiO2 focusing on water activation and the oxygen evolution mechanism on these heterostructures. Rutile and anatase TiO2 are modified with nanostructures of metal oxides, namely alkaline earth oxides, cerium oxide and manganese oxides; these are also being prepared and characterised at collaborators laboratories in the framework of an EU H2020 M-ERA.net 2 project RATOCAT.

We find that nanoclusters of these oxides with different compositions and adsorption modes are strongly adsorbed and can induce a red shift in light absorption towards the visible region of the electromagnetic spectrum. A simple model of the photoexcited state allows the localisation of electrons and holes produce by excitation to be determined and understood. Typically, DFT studies neglect key issues issues such as reducibility of the oxide or the role of adsorbed hydroxyls on the properties and the water activation processes in OER. We include a detailed analysis of reduction of the heterostructures, in which we find that loss of oxygen is generally favourable. In addition, the surface hydroxylation (through adsorption and dissociation of water) and the cluster hydroxylation are examined. We find that a single water molecule will dissociate at the supported oxide nanocluster, with large energy gain that indicates hydroxyl groups will be present and must be accounted for.

With a suitable model of a hydroxylated oxide heterostructure, including oxygen vacancies, we explore water activation and find for those structures with hydroxyls and single oxygen vacancies, the water adsorption is dissociative but with moderate energy gains. Too high an energy gain and the subsequent OER steps are not favourable. We determine the step with the highest free energy cost and use this to estimate an overpotential for these heterostructures as well as determining key aspects of these structures that drive favourable OER.

Support for this work from Science Foundation Ireland through the H2020 M-ERA.net 2 co-fund program, Grant Number 16/M-ERA/3418 is acknowledged. We also acknowledge access to computing resources through the SFI funded Irish Centre for High End Computing, ICHEC.
Enhanced Oxygen Evolution Reaction Performance of WO3/Nb:SrTiO3 Heterostructures By Graphene Layer
Authors: Cho Ayoung , Lee Joonbong , Youn Chulmin , Lee Sangwoo , Lee Ho Jin , Choi Taekjib
Published: May 2020

Photoelectrochemical (PEC) water splitting using photo-active nanomaterials is a promising technique to generate hydrogen in a sustainable way. The charge-transfer and charge separation in photoelectrode are important factors in determining the performance of PECs. Here, we utilize single layer graphene as a photocatalyst on WO3 thin film / Nb:SrTiO3 (100) structure to enhance oxygen evolution reaction in alkaline electrolyte. The graphene-decorated photoelectrodes exhibit efficient charge transfer due to electronic and electrochemical properties of graphene edges, which leads to decreasing onset potential and increasing photo current density from 237 μA/cm2 to 763 μA/cm2 at 1.23 V vs RHE. In addition, such extremely thin layer can protect the photoelectrode from chemical corrosion without disturbing the light absorption. We discuss the role of graphene edges for photoelectrochemical water oxidation. Thus, these results can provide a new route for advanced designs of nanomaterial-based PECs devices.

Acknowledgments This research was supported by next generation engineering researcher program of national research foundation of Korea (NRF) funded by the Ministry of Science, ICT (NRF-2019H1D8A2106002).
Oxygen Evolution Reaction/Oygen Reduction Reaction Properties of Massively Synthesized a NiMoS with Solvothermal Method
Authors: Choi Yusong , Ahn Tae-Young , Yu Heryeon , Kim Jiyoun , Cho Jang-hyeon
Published: May 2020

The oxygen electrode is the most important component in lithium-air batteries for oxygen reduction and evolution reaction (OER/ORR) to get closer to the theoretical energy density of 11,238 Wh/kg, which is the best among the batteries ever developed. Many carbon materials have been researched as a candidate oxygen electrode for lithium-air batteries such as a carbon black, CNTs and graphene. Compared to the many research results, there are still many controversies on the optimum oxygen electrode for lithium-air batteries. Besides that, carbon and binder have been known to deteriorate OER/ORR properties for lithium-air batteries by generating Li2CO3 and other bi-product. Recently, HER and OER properties of heterogeneous MoS2/Ni3S2 have been reported for water splitting. The heterogeneous HER and OER performances of MoS2/Ni3S2 were better than the commercial HER and OER catalysts. Up till now, to my best knowledge, there's no report on ORR properties for homogeneous NiMoS. Therefore, to investigate the ORR properties of homogeneous NiMoS, the homogeneous NiMoS has been synthesized on Ni-foam as well as Ni-powder by various solvothermal methods such as applying to stir during solvothermal synthesis, increasing the pressure or applying the both. Finally, we successfully synthesized NiMoS massively with stirring at the pressure of 15 bar. Characterization for NiMOSs variously synthesized were conducted with SEM, TEM as well as OER/ORR properties using RRDE (Ring Rotating Disk Electrode).

As a result, homogeneous NiMoSs massively synthesized with stirring as well as high pressure of over 15 bar shows a unique homogeneous structure with sub-micron size. However, NiMoS synthesized under 2~3bar pressure with no stirring shows the tens of micron size as well as heterogeneous structure. Intriguingly, OER/ORR properties of massively synthesized NiMoS shows much better OER/ORR properties compared to the solvothermal synthesized NiMoS with no-stirring and at the pressure of 2~3 bar. These results show a very optimistic result for non-precious electrode material for the next generation Li-air battery as well as the fuel cell field.
Highly Active and Durable Transition Metal Oxide-Based Oxygen Electrode Catalysts for Unitized Reversible Fuel Cells
Authors: Choi Sung Ryul , Choi Sungyong , Kim Dongyeong , Park Jun-Young
Published: May 2020

Facing with the increasing environmental concerns for global warming and environmental pollutions, it is essential to develop renewable and sustainable energy sources to substitute traditional fossil fuel-based technologies. As a major candidate technology, unitized reversible fuel cells (URFCs) are recognized as a promising electrochemical energy conversion device due to their high energy efficiency and negligible carbon emissions [1]. However, the low electrocatalytic activity related to the large overpotential loss for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is the key technical issue for the development of URFCs [2]. Until now, precious metal-based catalysts (e.g., Pt/C, Ir/C, and IrO2) have been used for OER and ORR in URFCs due to high electrocatalytic activity [3]. Nevertheless, making commercialization of URFCs has hampered by the scarcity and limited durability of these materials [4, 5]. In order to solve these technical barriers, non-precious transition metal oxide based materials have considered as promising alternatives for bifunctional OER and ORR electrocatalysts because of their low cost, earth-abundance, and long-term stability [6]. However, transition metal-based oxygen catalysts have several issues such as low electrical conductivity, small surface area, and low electroactivity. Herein, as main strategies to improve bifunctional electrocatalytic activity for OER and ORR, other transition metals are doped to increase intrinsic property of oxide materials with hybridizing with highly conductive carbonaceous materials as supporting material. The synthesized catalysts are analyzed by various physicochemical and electrochemical analysis tools [7. 8].

References

1. Landon, E. Demeter, N. Inoglu, C. Keturakis, I. Wachs, R. Vasic, A. Frenkel, and J. Kitchin, ACS. Catal.
8, 1793 (2012).

2. Fominykh, P. Chernev, I. Zaharieva, J. Sicklinger, G. Stefanic, M. Doblinger, A. Muller, A. Pokharel, S. Bocklein, C. Scheu, T. Bein, and D. F. Rohifing, ACS. Nano. 5, 5180 (2015).

3. Ren, Z. Ma, and P. G. Bruce, Chem. Soc. Rev. 41, 4909 (2012).

4. Han, N. Chen, J. Zhang and L. Qu, Mater. Horiz. 4, 832 (2017)

5. W. Louie, and A.T. Bell, J. Am. Chem. Soc. 33, 12329 (2013).

6. -F. Li, and A. Selloni, ACS Catal. 4, 1148 (2014).

7. -I. Kim, Y.J. Sa, S.-H. Cho, I. So, K. Kwon, S.H. Joo, and J.-Y. Park, J. Electrochem. Soc.
163, F3020 (2016).

8. -S. So, N.-I. Kim, S.-H. Cho, Y.-R. Kim, J. Yoo, Y. Seo, Y.-S. Seo, B. Park, K. Kwon, and J.-Y. Park, J. Electrochem. Soc.
163, F3041 (2016).

Keywords: Oxygen evolution reaction; Oxygen reduction reaction; Bifunctional electrocatalyst; Unitized reversible fuel cell; Transition metal oxide.
Gold-Ruthenium Alloy Nanofibers As a Bifunctional Electrocatalyst for Overall Water Splitting in Acidic Environments
Authors: Kwon Taehui , Yu Areum , Lee Chongmok , Lee Youngmi
Published: May 2020

Hydrogen is widely regarded as an environmentally-friendly and practical alternative energy to reduce reliance on fossil fuels. Also, hydrogen has the outstanding advantages of high energy storage density and sustainable reaction products. The most promising technology to produce hydrogen from abundant renewable sources is water electrolysis. Electrochemical water splitting involves two reaction systems, namely, an anodic oxygen evolution reaction (OER) and a cathodic hydrogen evolution reaction (HER). In general, typical HER catalysts with good activity in acidic solutions, such as Pt, exhibit poor activity in OER. Therefore, it is important to study bifunctional catalyst with high activity, efficiency and stability in acidic solutions.

In this presentation, we demonstrate the synthesis of AuRu alloy nanofibers as bifunctional electrocatalysts for water splitting. The Au/RuO2 nanocomposites are synthesized via electrospinning and calcination. After the subsequent reduction process, the AuRu alloy nanofibers are formed. The reduction process of Au/RuO2 nanocomposites to AuRu alloy nanofibers are investigated and the physical properties of AuRu alloy nanofibers in comparison to those of pure Au and Ru are analyzed with X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The morphologies of the Au/RuO2 nanocomposites and AuRu alloy nanofibers are confirmed with field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The electrocatalytic activity of AuRu alloy nanofibers are studied toward both OER and HER in Ar-saturated 0.5 M H2SO4 aqueous solution with rotating disk electrode (RDE) voltammetry. The Tafel slopes which represent kinetics of the reaction for OER and HER are obtained based on the corresponding RDE curves. In summary, this study presents the AuRu alloy nanofibers as a better bifunctional electrocatalyst for overall water splitting than Au/RuO2, RuO2, Ru, Pt/C, Ir/C, Au/C and Ru/C.

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT& Future Planning (NRF-2017R1A2A2A14001137).
MoS2@NiFe2O4/CB Hybrid As a Bifunctional Electrocatalyst for Water Splitting
Authors: Munonde Tshimangadzo Saddam , Zheng Haitao , Nomngongo Philiswa Nosizo
Published: May 2020

Designing effective bifunctional electrocatalysts for OER and HER at high current density with low overpotentials is essential to promote water splitting technology for renewable energy conversion and storage. MoS2 and NiFe2O4 are known functional materials for HER and OER in acidic and alkaline media, respectively. In this work, integrating MoS2 with NiFe2O4/CB in various ratios (1:1, 2:1 and 3:1) has been done to improve the catalytic performance of OER and HER. MoS2@NiFe2O4/CB (2:1) hybrid exhibited enhanced OER performance with a low onset potential of 1.38 V, lower overpotentials of 260 mV at j = 10 mA cm-2 and a low Tafel slope of 46 mV dec-1 in 1 M KOH. The hybrid also displayed excellent stability after 12 hrs OER electrolysis, with a negligible change in overpotentials showing ~ 2 % improvement. Besides the synergistic effects between NiFe2O4/CB and MoS2, the improved performance can be ascribed to the enhanced charge-transfer mechanism and texture properties allowing easy accessibility of electrolytes. Contrary to the OER performance, MoS2@NiFe2O4/CB (1:1) displayed the highest HER performance with a low onset potentials of 264 mV, lower overpotentials of 423 mV at j = 10 mA cm-2 and a low Tafel slope of 104 mV dec-1 in 0.5 M H2SO4, however the performance was lower than that of its individual components (NiFe2O4/CB and MoS2/CB. The low HER results of MoS2@NiFe2O4/CB (1:1) might have resulted from the sluggish kinetics observed. However, the hybrid shows excellent stability affording the similar i-V curves as the initial tests after 1000 cycles, thus MNFC hybrids show considerable potential to facilitate water splitting reactions.
La, Ni-Based Metal Oxides As Bifunctional Catalysts for the Oxygen Reduction and Evolution Reactions in Alkaline Medium
Authors: Chen Jiyun
Published: May 2020

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the fundamental processes occurring at the air electrode of metal-air batteries and reversible fuel cells. [1,2] However, the performance of those devices is hindered by the sluggish kinetics of both OER and ORR, and by the low stability and high cost of the catalysts. Here, we will present our recent studies on the one-dimensional (1D) La, Ni-based metal oxide [3] bifunctional catalysts which are characterized by excellent OER and ORR electrocatalytic activity and outstanding stability.

The catalysts were prepared by hydrothermal method and, by controlling the KOH concentration, 1D hydroxide precursors with different aspect ratios were synthesized. By using graphene (G) as the supporting material, a variety of La, Ni-based metal oxides such as Ni+La2O3/G, LaNiO3, and La2NiO4+NiO/G were synthesized, Figure 1. Electrochemical characterization of the catalysts showed that the aspect ratio of the materials has a significant effect on their electrocatalytic activity. Namely, Ni+La2O3/G nanorods have proven to be electrochemically active for ORR with a half-wave potential (E1/2) of 0.715 V vs RHE, and for OER with 1. 574 V vs RHE at 10.0 mA cm−2 (E10) in 0.1 M KOH. The performance of Ni+La2O3/G is close to that of commercial Pt/C (E1/2=0.830V) which is the most efficient catalyst of ORR, and significantly higher than commercial RuO2 (E10=1.633 V) and IrO2 (E10=1.663 V) for OER. The unique structural, morphological and electrocatalytic properties of the Ni+La2O3/G catalysts will be presented and discussed.

1. Sui, S.; Wang, X.; Zhou, X.; Su, Y.; Riffat, S.; Liu, C.-j., A comprehensive review of Pt electrocatalysts for the oxygen reduction reaction: Nanostructure, activity, mechanism and carbon support in PEM fuel cells. Journal of Materials Chemistry A 2017, 5 (5), 1808-1825.

2. Cheng, F.; Shen, J.; Peng, B.; Pan, Y.; Tao, Z.; Chen, J., Rapid room-temperature synthesis of nanocrystalline spinels as oxygen reduction and evolution electrocatalysts. Nature chemistry
2011,
3 (1), 79.

3. Singh, Sarika, Daria Zubenko, and Brian A. Rosen. "Influence of LaNiO3 shape on its solid-phase crystallization into coke-free reforming catalysts." ACS Catalysis 2016, 7 4199-4205.

Figure 1
The Path to Active and Stable Anion Exchange Membrane Water Electrolyzer
Authors: Faid Alaa Y , Barnett Alejandro Oyarce , Seland Frode , Sunde Svein
Published: May 2020

Renewable hydrogen generation is a crucial step to reach a sustainable society. Water electrolysis represents a cheap and effective method for hydrogen production. Anion-exchange membranes (AEM) water electrolysis utilizes inexpensive transition metal electrocatalysts, membranes, ionomers, and construction materials.1
,
2 In this work we report characterization of NiMo and NiCoFe catalysts that have been optimized as hydrogen and oxygen evolution reaction (HER and OER) catalysts. The characterization includes studies of ionomer-electrolyte-catalyst interaction as a basis for optimizing HER and OER performance under real operating conditions. With these optimized catalysts in an AEM electrolyzer we have achieved 1 A cm-2 at 1.95 V in 1 M KOH at 50 oC. The AEM electrolyzer was stable for 65 hours at 0.5 A cm-2 in 0.1 M KOH. The catalysts developed here will be significant in supporting the pursuit of cheap hydrogen fuel.

References

1 A. Faid, A. Oyarce Barnett, F. Seland, S. Sunde, A. Y. Faid, A. Oyarce Barnett, F. Seland, and S. Sunde, Catalysts, 2018, 8, 614.

2 A. Y. Faid, A. O. Barnett, F. Seland, and S. Sunde, J. Electrochem. Soc., 2019, 166, F519–F533.

Figure 1
A M-N3/C Active Site Prepared through Terpyridine Motifs (M= Fe, Co, Mn, Ni, Sn) for the Oxygen Reduction Reaction
Authors: Fruehwald Holly M , Zenkina Olena V , Easton E. Bradley
Published: May 2020

Non-noble catalysts for the oxygen reduction reaction (ORR) are in high demand for fuel cell technology due to their use of low cost and widely available starting materials. The development of these catalysts has been a constantly growing area. However, to the extent of our knowledge, there have only been a few literature reports that provide insights into the nature of the structure and geometry of the catalytically active sites formed in these materials.

In the current literature, the most commonly proposed catalytically active site(s) for ORR are active sites that correspond to Fe-N2+2/C geometry. These active sites are typically produced through a high-temperature pyrolysis step to obtain this desired configuration[1]. However, the pyrolysis step is very disadvantageous due to the production of a variety of nitrogen functional groups on the surface which can negatively affect the activity of the catalyst, since only nitrogen functionalities with specified geometry are considered to be the most active for ORR[2,3]. In addition, high-temperature treatments drastically increases the overall cost of production and can be quite energy demanding. Thus, high-temperature treatment makes it difficult to design a surface rich in a specific active site for the desired application.

We had previously developed a model of a catalyst rich in Fe-N3/C sites on a commercial Vulcan carbon. We showed that this site had high activity for the ORR reaction achieved by covalently functionalizing a carbon support with a nitrogen-rich terpyridine (tpy) ligand. The ligand geometry allowed for the formation of well-defined active sites on the carbon surface, leaving exposed N3 moities for the ORR. Metal-ligand coordination with Fe resulted in desired Fe-N3/C moieties on the surface. We demonstrated that this system can be prepared using mild reaction conditions and does not require high-temperature treatment for improved activity. On the contrary, the heat-treatment to this system was detrimental to the activity. Recently, we have been investigating the effect of other non-precious late transition metals for the activity of the novel N3/C sites. We present here the results of the M-N3/C site where M= Co, Sn, Ni, or Mn and show that these metals also show promising electrochemical activity in both acidic and basic media due to well-defined N3/C site for the ORR, showing generality of our initial results with iron and overall versatility and activity of an N3 site in combination with various non-precious metals for an ORR catalyst.

[1] M. Lefèvre, E. Proietti, F. Jaouen, J.-P. Dodelet, Science
2009, 324, 71-74.

[2] F. Charreteur, F. Jaouen, S. Ruggeri, J.-P. Dodelet, Electrochimica acta
2008, 53, 2925-2938.

[3] H. M. Fruehwald, I. I. Ebralidze, O. V. Zenkina, E. B. Easton, ChemElectroChem
2019, 6, 1350.

Figure 1
Novel Synthesis of Manganese Single Atom Oxygen Reduction Reaction Catalyst for Enhanced Stability in Polymer Electrolyte Membrane Fuel Cells
Authors: Stracensky Thomas Stephen , Yang Fan , Zhong Sichen , Jiao Li , Lattimer Judith , Jia Qingying , Mukerjee Sanjeev , Xu Hui
Published: May 2020

In an effort to viably implement polymer electrolyte membrane fuel cells (PEMFCs) technology, there has been a drive for the development of platinum group metal free (PGM-free) oxygen reduction reaction (ORR) catalysts. To this end, iron based catalysts such as the single atom FeN4 catalyst have been identified as one of the most active species for the ORR in the PEMFCs . However, while initial activity of the catalyst is high, the stability of membrane and electrode assemblies (MEAs) is still poor upon extended operations. One degradation mechanism for Fe-based MEAs can be attributed to the Fenton reactions that produce highly reactive radicals capable of attacking the membrane of the PEMFCs. Therefore, alternative catalysts that can mitigate Fenton reactions have been investigated to enhance the MEA stability in PEMFCs.

Manganese single atom based catalysts have risen recent interest as a candidate to circumvent the issue of radical formation and provide a highly active and stable catalyst for the ORR in PEMFCs1. In this work we have developed a novel pyrolysis synthetic method to form the Mn single atom catalyst. It was found that the pyrolysis temperature and precursor selection are crucial factors for developing a highly active ORR catalyst. The developed pyrolysis leads to minimal aggregation and forms active sites on the exterior of the catalyst particle that become available to perform oxygen reduction. The active site of this catalysts was validated by x-ray absorption spectroscopy (XAS) and the catalyst showed good activity for the ORR in PEMFCs. The catalyst also demonstrated excellent stability upon voltage cycling under nitrogen where oxygen exposure is seen to decrease the activity. The mechanism of degradation due to oxygen exposure is investigated under storage and during operation by examining the structural changes to the Mn species via XAS. Here it was found that under storage in air the catalyst formed Mn(III) oxides and when the MEA was cycled under oxygen Mn(II) oxides formed.

Acknowledgements: This work is financially supported by the Department of Energy’s Fuel Cell Technology Office under the award# DE-EE0008075

(1) Liu, K.; Qiao, Z.; Hwang, S.; Liu, Z.; Zhang, H.; Su, D.; Xu, H.; Wu, G.; Wang, G. Mn- and N- Doped Carbon as Promising Catalysts for Oxygen Reduction Reaction_ Theoretical Prediction and Experimental Validation. Applied Catalysis B: Environmental, (243) p. 195-203, 2019.
Cobalt/Dihydroxybenzimidazole-Derived Amorphous MOF TAL-2 As a Single Precursor for Trifunctional ORR/Oer/HER Electrocatalyst Material
Authors: Alam Mahboob , Ping Kefeng , Bhadoria Rohit , Kazimova Nargiz , Starkov Pavel , Kongi Nadezda
Published: May 2020

Preparation of cost-efficient noble metal-free multifunctional electrocatalyst materials with high performance and stability for oxygen evolution reaction (OER), oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) – referred to as trifunctional catalysts – remains an outstanding challenge. The catalyst material was prepared from amorphous metal–organic framework TAL-2, which was obtained from cobalt salt and dihydroxybenzimidazole and outperformed the benchmark catalysts in ORR and OER reactions (0.1 M KOH; ∆E = 0.73 V, AMFCs: j = 1100 mA cm–2, P = 400 mW cm–2). Use of dopants or modifying conditions was unnecessary fot this material to be used as a trifunctional electrocatalyst.
Cobalt and Nitrogen Co-Doped Peat Derived Carbon Based Catalysts for Oxygen Reduction
Authors: Jäger Rutha , Teppor Patrick , Härk Eneli , Härmas Meelis , Adamson Anu , Paalo Maarja , Volobujeva Olga , Kikas Arvo , Kochovski Zdravko , Romann Tavo , Härmas Riinu , Lust Enn
Published: May 2020

The carbon precursor peat is one out of many mineral-rich resources of Estonia, which originally is a sediment of incompletely decomposed plant residues. The chemical properties of peat include the five basic elements: C, H, O, N and S [1]. Therefore, its composition is attractive and economically perspective not only for the synthesis of nonprecious catalysts for the oxygen reduction reaction (ORR), but also as a framework for batteries [2]. Generally, nonprecious metal and nitrogen co-doped catalysts have been synthesized using a metal salt, a nitrogen precursor and a carbon material via either one or multiple step preparation methods [3,4]. Herein, we introduce promising peat derived carbon (PDC) based cobalt and nitrogen co-doped catalysts (Co-N/PDCX) which demonstrate high catalytic activity towards ORR. The nanoporous carbon support was derived from peat via five different carbonization protocols (see Scheme). All the prepared PDCX and Co-N/PDCX catalysts were characterized by several physical characterization methods. The ORR activity of the synthesized PDCX and Co-N/PDCX catalysts were investigated in 0.1 M HClO4 solutions using rotating disc electrode method and the ORR activity of Co-N/PDCX shows significant dependence on the carbonization method used to derive a carbon support. The best catalyst was chosen for further testing in a fuel cell.

Acknowledgements

This work was supported by the EU through the European Regional Development Fund under project TK141 “Advanced materials and high-technology devices for energy recuperation systems” (2014-2020.4.01.15-0011), by the Estonian institutional research grant No. IUT20-13, NAMUR ”Nanomaterials - research and applications” (3.2.0304.12-0397) and LLTOM17351 “Activated carbon from peat” (01.07.2017-30.06.2020).

References

[1] Y. Uraki, Y. Tamai, M. Ogawa, S. Gaman, S. Tokura, BioResources, 2009, 4(1), 205-213.

[2] J. Ding, H. Wang, Z. Li, A. Kohandehghan, K. Cui, Z. Xu, B. Zahiri, X. Tan, E.M. Loftabad, B. Olsen, D. Mitlin, ACS Nano, 2013, 7(12), 11004-11015.

[3] F. Roncaroli, E.S. Dal Molin, F.A. Viva, M.M. Bruno, E.B. Halac, Electrochimica Acta, 2015, 174, 66–77.

Figure 1
(Invited) Exploiting New Electrolytes and Mechanistic Solvation Kinetics for Extreme Low Temperature Batteries
Authors: Chen Zheng
Published: May 2020

Improving the extremely low temperature operation of rechargeable batteries is vital to the operation of electronics in extreme environments, where systems capable of high-rate discharge are in short supply. Herein, we demonstrate the holistic design of dual-graphite batteries, which circumvent the sluggish ion desolvation process found in typical lithium-ion batteries during discharge. These batteries were enabled by a novel electrolyte, which simultaneously provided high electrochemical stability and ionic conductivity at low temperature. The dual-graphite cells, when compared to industry-type graphite || LiCoO2 full-cells demonstrated an 11 times increased capacity retention at -60 oC for a 10 C discharge rate, indicative of the superior kinetics of the “dual-ion” storage mechanism. These trends are further supported by GITT and EIS measurements at reduced temperature. This work provides a new design strategy for extreme low-temperature batteries. In addition, the electrolytes developed for dual-ion cells have also been extended to search for other high-capacity, high-rate electrodes, which leads to further improved energy density and stability for both high and extremely low temperatures.
Stability of Ionic-Covalently Cross-Linked PBI-Blended Membranes for so2 electrolysis at Elevated Temperatures
Authors: Peach Retha , Krieg Henning , Kruger Andries , Bessarabov Dmitri , Kerres Jochen A.
Published: May 2020

In this study, the effect of component composition on the chemical stability of the developed ionic-covalently cross-linked PBI-blended membrane concept from earlier studies for application in SO2 electrolysis at elevated temperatures (>100 °C) is further investigated. Three different acid-base ratios were studied by blending a partially fluorinated sulfonated arylene main-chain polymer (SFS) with polybenzimidazole (F6PBI) and a partially or non-fluorinated bromo-methylated polymer (BrPAE). In addition two different alkylated imidazoles (EMIm and TMIm) were included as quaternization agents. Accordingly, twelve different PBI-blended membranes were used in this study. The suitability of these membranes for SO2 electrolysis at elevated temperatures was determined in terms of i) the H2SO4 stability (80 wt% H2SO4 at 100 °C for 120 hours), (ii) the oxidative stability (Fenton’s test, FT) and (iii) the organic solvent stability (extraction in N,N-Dimethylacetamide). Membranes were characterized in terms of the percentage weight, the ion exchange capacity (IEC) and the thermal stability (TGA-FTIR) changes, before and after the various treatments. Although all blended membrane types were sufficiently stable during H2SO4 treatment, proton conductivity measurements indicated that the blends containing only partially fluorinated blend components displayed superior stability (better compatibility) as well as conductivity. Cell voltages showed an improvement of up to 190 mV for operations at 120 °C compared to earlier studies conducted at 80 °C for similar PBI-blended membranes. It was established that both chemically stable and conductive PBI-blended membranes, suitable for SO2 electrolysis above 100 °C, could be obtained by varying the composition of selected polymer components.

Figure 1: Schematic of the ionic-covalently cross-linking concept for the blend membranes (black – BrPAE, purple – F6PBI, blue – EMIm, and brown - sPPSU).

Figure 1
Effect of Microporous Layer (MPL) and Carbon Fiber Paper (CFP) Properties on PEMFC High Current Density Performance
Authors: Niangar Ely , Vora Mehul , Koestner Roland John , Kumaraguru Swami
Published: May 2020

The effect of microporous layer (MPL) and carbon fiber paper (CFP) properties on high current density cell performance is investigated in this work. Two types of carbon black (Denka Li-400 and Soltex AB50-HC) were used with the same MPL ink formulation using FEP as hydrophobic agent, and the inks were coated on two types of wetproofed CFP substrates. The resulting GDLs (CFP + MPL) have different, contrasting through-plane thermal conductivities – for the MPLs coated on Toray TGP-H-060, k = 0.310 – 0.390 W/mK but for those coated on Freudenberg H2312, k = 0.170 – 0.210 W/mK (under 2 MPa compression).

The MPL coatings were characterized by mercury porosimetry and scanning electron microscopy (SEM) (top-down and cross-section). The two MPLs show contrasting peak pore sizes – the AB50-HC MPL peak pore size is at 60 nm while the Li-400 MPL peak pore size is at 300 nm, consistent with recent MPL studies using Li-400 in the MPL [1]. Single cell membrane electrode assemblies (MEAs) were made in a catalyst-coated membrane (CCM) configuration at both 5 cm2 (for testing under differential flow conditions) and 38 cm2 (non-differential cell) active areas. Polarization curves at different operating conditions were obtained in addition to limiting current experiments (on 5 cm2 differential cells) to determine the total oxygen transport resistance.

At dry operating conditions (Tcell = 80°C, RH = 32%, pabs = 150 kPa), the cell performance of all four (4) samples (2 MPLs coated on 2 different CFP substrates) are comparable, but under wet operating conditions, (Tcell = 80°C, RH = 100%, pabs = 150 kPa), the 2 MPLs (AB50-HC and Li-400) coated on TGP-H-060 have significantly lower cell performance (38 cm2 non-differential cells, but the same trends were observed when testing under differential flow conditions (5 cm2 CCM MEAs)). These results reiterate the importance of GDL through-plane thermal conductivity as the main GDL property that influences water management and controls cell performance at high current densities (> 2.0 A/cm2) [2].

References

1. C Simon, H Gasteiger et. al., Impact of Microporous Layer Pore Properties on Liquid Water Transport in PEM Fue Cells: Carbon Black Type and Perforation, J. Electrochem. Soc., 2017, 164 (14), F1697- F1711

2. J Owejan, M Mathias et. al., Water Transport Mechanisms in PEMFC Gas Diffusion Layers, J. Electrochem. Soc., 2010, 157 (10), B1456- B1464

Figure 1