bluuebunny/crossref_metadata_2025 huggingface dataset:
SnP2O7 Based Membranes for Intermediate Temperature Electrochemical-Synthesis of Ammonia
Authors: Ramaiyan Kannan Pasupathikovil , Maurya Sandip , Kim Yu Seung , Garzon Fernando H , Mukundan Rangachary , Kreller Cortney R.
Published: February 2020

Electrochemical synthesis of useful chemicals such as ammonia through renewable electricity will ease problems associated with renewable energy storage. However, the strong NºN bond (941 kJ mol-1) poses a severe challenge for mild condition synthesis of ammonia. Several attempts toward electrosynthesizing ammonia at low and high temperatures included a variety of electrode materials ranging from glassy carbon electrode to precious metals and different proton and oxide ion conducting electrolytes [1]. Rates on the order of 10-9 mols-1cm-2 have been reported for both low and high temperature systems. While the formation of ammonia from H2 and N2 is exothermic, at low temperatures the reaction kinetics is too low for industrial production. The current high temperature Haber-Bosch process is too energy intensive and is not economically viable for small scale remote applications.

We report the synthesis of ammonia in a simple fuel cell configuration using a Sn2P2O7 – nafion composite membrane and Pt electrodes in the low-intermediate temperature range of 200-300°C. The composite membrane showed conductivity values in the range of 10 – 20 mScm-1 at 200°C. Our membranes retained high conductivity values after continuous operation over 300 hours. We observed an ammonia synthesis rate of 1.8x10-9 mols-1cm-2 under a bias of -0.1 V with Pt based electrodes and H2 and N2 as reactant gases.

References

V. Kyriakou, I. Garagounis, e. Vasileiou, A. Vourros, and M. Stoukides, Catalysis Today, 2016 http://dx.doi.org/10.1016/j.cattod.2016.06.014.
Effect of Carbon Support and Synthesis Method on Pt NP Utilization and Activity
Authors: Ketabi Sanaz , El Sawy Ehab N , Birss Viola
Published: February 2020

A key requirement for the large-scale commercialization of proton exchange membrane (PEM) fuel cells is to produce highly active, durable catalysts, while minimizing the use of precious noble metals, especially platinum (Pt). Higher utilization of Pt catalyst can be realized by understanding the effect of the carbon support microstructure on the distribution and formation of Pt nanoparticles (NPs) and by optimizing the synthesis method. In this work, Pt NPs were fabricated using a simple alcohol reduction method and then varying the carbon support pore structure and surface properties. The catalysts were then tested for their activity in 1 M C2H5OH + 0.5 M H2SO4 solutions.

For Pt NP preparation, either ethanol or butanol were used as the solvent and reductant. The ethanolic or butanolic solution containing H2PtCl6 was then added to the carbon support dispersed in the same solvent at room temperature, and the mixture was heated at the boiling point for 2 hrs. In the case of the ethanol solvent, an aqueous alkaline solution was added to ensure the completion of Pt reduction [1]. However, this step was not used during synthesis when using butanol, due to its higher reducing power. Three types of carbon supports were investigated, Vulcan carbon (VC), Ketjenblack (KB), and colloid-imprinted carbon powders (CICs). The structure and distribution of the Pt NPs were confirmed by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM).

Figure 1 shows the cyclic voltammograms of JM Pt/VC and Pt/CIC85 (i.e., 85 nm pore size), prepared by both the ethanol and butanol synthesis methods, in 0.5 M H2SO4. Even though the theoretical specific surface areas were 70-80 m2/gPt (particle size of 3-3.5 nm), the electrochemical active surface area (ECSA) was found to depend on the synthesis method and the carbon support. The ethanol oxidation activity of catalysts per Pt area for the three carbon supports is shown in Figure 2. A strong dependence on the carbon microstructure was observed, with Pt/CIC and Pt/KB, showing a higher activity than Pt/VC, likely due to their higher content of mesopores in the catalyst layer [2]. The correlation between catalyst activity and the carbon microstructure for each synthesis method will be discussed in detail.

References:

1. J. Xie, Q. Zhang, L. Gu, S. Xu, P. Wang, J. Liu, Y. Ding, Y.F. Yao, C. Nan, M. Zhao, Y. You, Z. Zou, Nano Energy (2016) 21, 247–257.

2. T. Soboleva, X. Zhao, K. Malek, Z. Xie, T. Navessin, S. Holdcroft, ACS applied materials and interfaces (2010) 2, 2, 375–384.

Figure 1
Interpretation of Nyquist Plot for Characterization of Electrode and Electrolyte Material Properties for Electrical Double Layer Capacitors
Authors: Mei Bing-Ang , Pilon Laurent
Published: February 2020

Electric double layer capacitors (EDLCs) store energy via ion adsorption in the electric double layer forming at the electrode/electrolyte interfaces. This charge storage mechanism is very fast and highly reversible resulting in large power density and long cycle life. Applications range from regenerative breaking for hybrid electric vehicles to the smart grid. Electrochemical impedance spectroscopy (EIS) has been used widely to determine the properties of the electrode and electrolyte materials for EDLCs. The impedance of an EDLC half-cell can be measured by applying a low-amplitude sinusoidal voltage to a steady-state potential and divide the imposed potential by the output sinusoidal current. Nyquist plots showing the imaginary part as a function of the real part of the impedance is informative to determine the properties including electrode and electrolyte resistance, charge transfer or polarization resistance at the electrode/electrolyte interface, and capacitance of the half-cell. However, the interpretation of Nyquist plots has been a “subject of controversy”, with no clear relations between the shape in high, intermediate, and low frequency regime of the plot and a particular property of the device.

This study aims to derive guidelines for characterization of EDLC electrode and electrolyte materials from EIS measurements. To do so, Nyquist plots from EIC measurements were numerically reproduced for EDLC half-cells with planar electrodes in aqueous TEABF4 electrolyte. The continuum model used was based on the modified Poisson-Nernst-Planck model and accounted for (i) the Stern layer at the electrode/electrolyte interface, (ii) finite ion size, and (iii) binary and symmetric electrolyte. The effect of the electrode and electrolyte resistance, charge transfer or polarization resistance at the electrode/electrolyte interface, and the capacitances were separated numerically. This was done by varying the bulk ion concentration, electrolyte length, ion diffusion coefficient in the electrolyte, and/or the magnitude of steady-state potential. Therefore, the behaviour in each frequency regime in Nyquist plots that corresponded to a particular property was clarified.
Visualizing and Control Ion Transport and Phase Transition Processes in Epitaxial Oxide Thin Films
Authors: Du Yingge
Published: February 2020

Complex oxide materials with ordered vacant lattice sites enable facile, synchronous electron/ion intercalation reactions, and have been extensively investigated for energy conversion and storage applications. A topotactic phase transition (TPT), in which the final crystal lattice is closely related to that of the original material, may occur through the displacement and exchange of atoms as a result of charge and mass transfer. Even though the change in crystal structure is small, a TPT can significantly alter the electronic structure, lattice charge, and physical properties of a material.

In this talk, I will show that thin-film deposition by molecular beam epitaxy (MBE) allows ultrahigh purity materials of this kind to be synthesized, together with accurate control over their thickness, doping level, and strain state for predictable structural and property modifications. In combination with advanced transmission electron microscopy (TEM), secondary ion mass spectrometry (SIMS), and theoretical modeling, we were able to characterize and simulate ion transport and phase transition processes at a comparable length scale to provide fundamental insight into these processes. In one example, we show that ordered oxygen vacancy planes in SrCrO3-δ under different strain states (compressive vs. tensile) displays drastically different phase stability and O2- ion transport properties, which is of considerable interest in solid oxide fuel cells where fast oxygen ion transport at lower operating temperature is highly desired. In another example, I will present how we tune the structure and electronic properties of WO3 epitaxial thin films, and use them as model cathode materials for in situ TEM studies. The atomic scale ion (Li+, Na+, and Ca2+) intercalation, accompanied with a monoclinic to cubic phase transition, together with subsequent conversion reactions are revealed by STEM, EELS, NBD, and theory.
Investigation of a Correlation Between Carbon Corrosion and Proton Conductivity of Ionomers in PEFC Under the Low Humidity Operation
Authors: Hayashi Akari , Miyamoto Hidemasa , Kitamura Masahiko , Sasaki Kazunari
Published: February 2020

One of the strategies to further increase PEFC performance is elevation of the operation temperature. However, durability of materials used in PEFC is assumed to be lowered at the higher temperature condition, which is also accompanied by the lower humidity condition. We have been studying degradation phenomena of cathode catalyst layers at the higher temperature. During our study, we have found carbon corrosion is related to the proton conductivity of ionomers in cathode catalyst layers when PEFC is operated at the higher temperature with lower humidity. Therefore, in this study, a correlation between carbon corrosion and proton conductivity of ionomers has been investigated.

MEAs were prepared using a standard catalyst and two types of electrolytes, Pt/Ketjen black catalyst (TEC10E50E, TKK Corp.), and Nafion® and Aquivion®, respectively. Here, The Aquivion® has higher proton conductivity than Nafion®. The operating condition of the higher temperature with lower humidity, 105 °C-RH57%, was applied. Durability of MEAs was studied through the potential cycles between 1.0 and 1.5 V assuming “stop/start cycles” of FCVs.[1], [2]

Durability of two different MEAs (Nafion® MEA and Aquivion® MEA) was evaluated in terms of electrochemical and structural changes before and after the cycle test. Here, structural changes were analyzed using a FIB-SEM technique followed by 3D reconstruction of cathode catalyst layers. Although current–voltage curves were not very much different between two types of MEAs even after 2000 cycles, the macroporous structures of catalyst layers were different. Porosity was almost homogeneous through the catalyst layer in Aquivion® MEA, but larger pores intensely formed near the Nafion® membrane side in the case of Nafion® MEA. The possible degradation mechanism is illustrated in Fig.1 and explained in the following. The carbon oxidation reaction probably occurs mainly by reacting with H2O being formed by a fuel cell reaction if it is under the low humidity condition. If proton conductivity is high enough like Aquivion® ionomer, H2O is probably generated more uniformly and carbon oxidation also occurs uniformly throughout the cathode catalyst layers. On the other hand, when proton conductivity is low like Nafion® ionomer, H2O is mainly generated at the interface between the cathode layer and Nafion® membrane. Then, carbon oxidation intensely occurs at the interface between the cathode and the electrolyte membrane.

Reference

[1] A. Ohma et al., ECS Trans, 41 (2011) 755.

[2] H. Miyamoto et al., ECS Trans, 75 (2016) 329.

Figure 1
Design Considerations for a Robust Electrode of PEMFC Under H2 Starvation
Authors: Lee Hoonhee , Choi Jinsung , Roh Bumwook
Published: February 2020

In PEMFC stacks for automotive applications, the insufficient reactants (hydrogen and air) can be resulted from the undesirable conditions such as water flooding in electrodes or gas channel, ice formation in subzero temperature, and unexpected defects in gas diffusion layer or in gas channel of bipolar plates. Particularly, the lack of hydrogen gas can lead to the carbon oxidation at anode, resulting in the severe cell degradation, which is called as cell voltage reversal. In order to prevent this unexpected performance degradation of fuel cells, we developed a new anode with excellent reversal voltage tolerance by introducing a known water electrolysis catalyst into anode system (Pt/C-based catalyst). As a result, a membrane-electrode-assembly (MEA) with very high resistance to cell voltage reversal was achieved with the new anode. The effect of relative humidity (RH) of supplied gas to the behaviors of cell voltage under reversal voltage condition was investigated. Also, the importance of RH for the supplied gases to anode and cathode was demonstrated. Lastly, the effect of cell reversal exposed time and the number of voltage reversal tolerance cycle for the anode.
High Performance Pt-Ni Nanocage Catalyst for the Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells (PEMFCs)
Authors: Peng Xiong , Omasta Travis J , Rigdon William A. , Mustain William E
Published: February 2020

PEMFCs have long been considered to be among the most promising next-generation energy conversion systems for portable devices and transportation vehicles due to their zero or low pollution, high power density and low temperature operation1,2. However, the widespread commercialization of PEMFCs remains challenged by the high cost of cell components and limited cell durability. Therefore, there is a significant need to develop new catalyst materials with high intrinsic oxygen reduction reaction (ORR) activity and stability, as well as a fabrication process that leads to high cell performance and durability with low catalyst loadings.

In this work, we investigate the activity and stability of Pt-Ni nanocage oxygen reduction electrocatalysts (Figure 1a) both ex-situ and in-situ in an operating PEMFC. Ex-situ, the catalysts were both physically and electrochemically characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and both cyclic and linear sweep voltammetry using a rotating disk electrode (RDE). The nanocages showed 2 and 4 times greater specific and mass activity than Pt/C, respectively, for the ORR with high durability.

The catalysts were transitioned from the RDE platform to operating PEMFCs by application onto a Nafion® 212 membrane to form a catalyst-coated membrane (CCM) with a low cost, custom-built air-assisted cylindrical liquid jet spraying system (ACLJS). Several ACLJS parameters were investigated and the optimized parameters were used to produce CCMs that were tested by scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), electrochemical impedance spectroscopy (EIS), PEMFC polarization and cyclic voltammetry. The CCM prepared with the Pt-Ni nanocage catalyst showed no obvious Pt and Ni dissolution and redeposition in the membrane even after 30K cycles. The performance and mass activity retention of the Pt-Ni nanocage catalyst was far superior to commercial Pt/C and just short of the US Department of Energy (DOE) 2020 targets3 (Figure 1 b,c), suggesting that Pt-alloy nanocages are very promising candidates for high-performing commercial PEMFCs.

References:

1. Service, R. F. FUEL CELLS: Shrinking Fuel Cells Promise Power in Your Pocket. Science (80-. ).
296, 1222–1224 (2002).

2. CLEGHORN, S. Pem fuel cells for transportation and stationary power generation applications. Int. J. Hydrogen Energy
22, 1137–1144 (1997).

3. (U.S. Department of Energy). Fuel Cell Technical Team Roadmap. Usdrive 9 (2013).

Figure 1
Sonochemical Reduction Method for Synthesis of TiO2-Pd Nanocomposites and Investigation of Anode and Cathode Catalyst for Ethanol Oxidation and Oxygen Reduction Reaction in Alkaline Medium
Authors: Wu Jerry
Published: February 2020

This paper describes a sonochemical approach for the synthesis of titanium dioxide nanospheres (TiO2) decorated by palladium nanoparticles (Pd NPs). In this method, the TiO2 nanospheres could be directly used as templates for the nucleation and growth of Pd NPs over their surface using PdCl4
- as the Pd precursor, PVP as the stabilizer, ascorbic acid (AA) as the reducing agent, and water as the solvent. The Pd NPs presented uniform distribution over the TiO2 nanospheres. Remarkably, the size of Pd NPs can be controlled by sequential reduction steps with adding excess of PdCl4
-. The TEM images are well explained that controlled size of Pd NPs as shown in Fig. 1. The electrocatalytic activity of TiO2-Pd electrode materials with size dependent Pd NPs was investigated towards the oxidation of ethanol and reduction of oxygen under alkaline medium. The results indicate that the nanocomposites materials are recognized to be an excellent electrocatalyst due to their excellent corrosion resistance and larger electrochemical active surface area.
Porous Iron-Nitrogen-Carbon Nanofiber As Efficient Oxygen Reduction Reaction Catalyst and Durable Support for Platinum
Authors: Kim MinJoong , Lim Jeonghoon , Cho EunAe
Published: February 2020

Polymer electrolyte membrane fuel cells (PEMFCs) have been considered as one of the most promising energy conversion devices for future due to their high efficiency, and environmental friendly system. However, large-scale applications of PEMFCs have still faced some challenges in terms of cost and durability. Catalyst plays a great role in determining cost and durability of PEMFCs. Conventional catalyst for PEMFCs is a state-of-the-art carbon supported platinum nanoparticles (Pt/C). Pt/C has an outstanding catalytic activity for both hydrogen oxidation reaction (HOR) at anode and oxygen reduction reaction (ORR) at cathode. But, high price of Pt is a major contributory factor in increasing PEMFCs cost. And, conventional carbon support is vulnerable to corrosion under oxidative potential, which leads to serious degradation of cell performance. Therefore, it has been one of the major issue in PEMFCs to develop low-priced and durable catalysts without sacrificing catalytic performance. Recent studies proposed that co-doping of transition metal (Fe, Co, Mn..) and nitrogen into graphene-like carbon structure can draw remarkable ORR activity under PEMFCs operating conditions. In addition, this graphene-like carbonaceous materials also can have higher corrosion resistance than conventional carbon support with amorphous structure.

Herein, we synthesized iron (Fe) and nitrogen co-doped carbon nanofiber (Fe-N-CNF) with highly porous structure as efficient oxygen reduction reaction catalyst and durable support for platinum catalyst. We could successfully synthesize porous CNF by using silica nanoparticles (SiO2 NPs) as sacrificing materials. After leaching of SiO2 NPs, BET surface area and electrochemical surface area (ECSA) were 3-times and 6-times enhanced, respectively. So, porous Fe-N-CNF has excellent ORR activity and durability in acidic media.

Fig. 1. TEM images of Fe-N-CNF and porous Fe-N-CNF

Figure 1
Evaluation of Order Mesoporous Carbon As Anode Catalyst for Microbial Fuel Cells
Authors: Garcia-Mayagoitia S. , Fernández-Luqueño F. , Morales-Acosta D. , Sanchez-Padilla N. M. , Rodriguez-Varela F.J.
Published: February 2020

Ordered Mesoporous Carbon (OMC) synthesized via self-assembly in aqueous phase, was evaluated as anode catalyst for Microbial Fuel Cells (MFCs) applications. Prior to electrochemical characterization, OMC was functionalized with methanol. The catalytic activity of non-funtionalized and functionalized OMC was compared to that of commercial Vulcan XC-72 and Graphite flakes (non-functionalized and functionalzied with methanol as well). Gas diffusion electrodes containig a catalytic layer of the catalysts were prepared by the painting technique. The Bacilus Subtilis microorganism was used to grow a biofilm over the carbonaceous catalysts and promote the bioelectrochemical reactions, while residual water directly from a pharmaceutical company (pH=9.6) was the electrolyte. Half-cell characterization was carried out in a three-electrode cell, at which Functionalized OMC showed the highest current density generated from the bioelectrochemical reactions occurring from the residual water. A dual chamber MFC was implemented, where the anode chamber contained residual water in N2 atmosphere, while the electrolyte at the cathode was O2-saturated KOH (pH=9.6). The anode catalysts were: Functionalized OMC, non-Funtionalized OMC, Functionalized Vulcan and commercial 20 % Pt/C, all containing a biofilm by Bacilus Subtilis. The cathode catalyst was commercial 20 % Pt/C. The characterization of the the MFC showed a significantly higher catalytic activity of Functionalized OMC + Bacilus Subtilis for the reactions. It delivered an Open Circuit Voltage (OCV) of 0.58 V and a maximum current density (jcell) of 854 mA m-2. These values were higher than those of Pt/C (2.6 and 4.7 higher OCV and jcell, respectively). The results showed that methanol-Functionalized OMC is a metal-free catalyst with high performance for MFCs.
Evaluation of the Dimensional Stability and Conductivity of PEM in Aqueous Solutions of Formic Acid for Use in Dfafcs
Authors: Holmes Stuart , Gonzalez Rodriguez Romeo , Perez Page Maria , Sellin Remy
Published: February 2020

Global energy consumption is one of the greatest problems humanity is facing and the need for viable and environmentally friendly alternative energy sources is rising. One of these alternative technologies is Direct Formic Acid Fuel Cells (DFAFCs) a promising alternative energy source for the constantly increasing energy demand; they have major potential for use in portable devices as they can perform extremely well at ambient temperatures and have a low environmental footprint.

Due to the low permeability of formic acid through the polymer exchange membrane (PEM) it allows work at higher concentrations leading to higher energy production compared to other fuel cells. Working under similar operating conditions DFAFCs can generate power densities of 233 mW/cm2 outperforming Direct Methanol Fuel Cells (DMFCs) with power densities of 53 mW/cm2 (1).

However, no fundamental studies about the intrinsic conductivity and dimensional stability of PEM have been carried out whilst under use of formic acid with the purpose of understanding how PEM behave under such highly acidic conditions. This is vital for understanding the long term performance and durability of such fuel cells, should they be used on a wider scale.

The studies carried out have examined how the PEM, including Nafion 115,117,211 and 212, behave and perform under varying acidic conditions. For the dimensional stability study optical analysis was carried out to determine the changes occurring in-situ to the material. In addition, determining changes in resistance using impedance spectroscopy allows for the selection of the most efficient membrane configuration for optimal cell operation.

Previous research has shown that Nafion with a lower equivalent weight has an increased hydrophilic region, compared with membranes with higher equivalent weight. Using this relationship to understand the performance of Nafion suggests that a higher hydrophilic region leads to deformity by the formic acid on the membrane. We have observed this as a change in the dimension of the membrane in only one direction; a change that is not observed when the membrane is immersed in water alone, where the changes in the dimensions are uniform in two directions. There are two possible causes of this; firstly by the production process of the membrane or that a change is taking place in the hydrophobic regions the continuous semi- crystalline TFE structure of the material. In this work we will explain the cause of the deformation.

1. 2-D Crystals Significantly Enhance the Performance of a Working Fuel Cell. Stuart M. Holmes*, Prabhuraj Balakrishnan, Vasu. S. Kalangi, Pulickel M. Ajayan, Xiang Zhang, Marcelo Lozada-Hidalgo and Rahul R. Nair. 27.09.2016., Advanced Energy Materials.
Enhanced Electrocatalytic Activities of Perovskite Electrocatalysts for the Oxidation of Small Molecules By Active Site Variation
Authors: Stevenson Keith J , Forslund Robin , Johnston Keith P.
Published: February 2020

The electrooxidation of urea and other small molecules has attracted considerable attention the anodic reaction for the electrochemical generation of hydrogen due to the lower electrochemical potential required to drive the reaction. Nickel and nickel-based materials have shown comparable activities to precious metal catalysts for the electrooxidation of urea and other small molecules in alkaline conditions. By incorporating nickel into the perovskite structure as well as derivatives of the perovskite structure, higher oxidation states of nickel active sites can be achieved, leading to increased catalytic activities at a fraction of the cost of other nickel-rich materials. While these materials are shown to be stable at low overpotentials, in depth mechanistic studies reveal restructuring of the catalyst surface and apparent deactivation due to poisoning from CO2 upon extended cycling, an occurrence that may be extended to describe catalyst deactivation in other nickel-based materials.
Durable Engineered Carbon Supports
Authors: Halevi Barr , Lubers Alia , McCool Geoff , McKinney Samuel , Romero Henry
Published: February 2020

A key limitation to catalysts today arises from reliance on carbon black (CB) supports that serve to disperse the precious metal catalyst nanoparticles, but which corrode under certain operating conditions. Carbon support modifications that rely on "top-down" graphitization of CB supports have so far improved resistance to carbon corrosion, but at the cost of reduced stabilization of precious metal dissolution.

Pajarito Powder developed a "bottom-up" approach where Engineered Carbon Supports (ECSs) made using the VariPoreTM manufacturing platform, which is cased on technologies licensed from the University of New Mexico, Northeastern University, and Los Alamos National Laboratory. This method allows manufacture of highly graphitic carbonaceous powders with excellent pore size and particle roughness control, and produces highly tailorable carbon support with great corrosion resistance.

Pt/C electro-catalysts made using these Engineered Carbon Supports maintain performance under carbon corrosion test protocols and thus demonstrate their utility in achieving the performance/price balance needed for commercializing PEMFCs. The catalyst characteristics and performance, as well as economics of this approach will be presented and discussed.
Tomography Aided Development of Membrane Electrode Assemblies for PEM Water Electrolysis
Authors: Hegge Friedemann , Vierrath Severin , Ogawa Shohei , Zielke Lukas , Bühler Melanie , Klose Carolin , Zengerle Roland , Litster Shawn , Thiele Simon
Published: February 2020

In polymer electrolyte membrane water electrolysis (PEMWE) the anode is crucial for the overall performance. State-of-the-art anodes comprise Ir, IrOx or IrRuOx, typically bound by an ionomer and can be TiOx supported [1]. Besides the material also the microstructure of the anode has an impact on the electrolyzer’s performance as it determines catalyst accessibility and species transport [2]. Optimizing the microstructure therefore offers a potential to increase cell efficiency. In our approach we use tomographic methods in order to establish a microstructure-performance relation for PEMWE anodes (see microstructure of a FuelCellsEtc PEMWE anode in Fig.1). We then apply our findings from the reconstructed anodes in order to develop improved membrane electrode assemblies (MEAs) for PEMWEs with novel manufacturing and design approaches. The experimental data will then be used as input for our theoretical models.

References

1. Carmo, M., Fritz, D.L., Mergel, J., Stolten, D.: A comprehensive review on PEM water electrolysis. International Journal of Hydrogen Energy 38(12), 4901–4934 (2013). doi: 10.1016/j.ijhydene.2013.01.151

2. García-Valverde, R., Espinosa, N., Urbina, A.: Simple PEM water electrolyser model and experimental validation. International Journal of Hydrogen Energy 37(2), 1927–1938 (2012). doi: 10.1016/j.ijhydene.2011.09.027

Fig. 1 SEM image (a) and three-dimensional representation (b) of an anode catalyst layer from a FuelCellsEtc electrolysis MEA reconstructed via nano computed tomography.

Figure 1
3D Printed Bipolar Plate for Water Electrolysis
Authors: Zhang Feng-Yuan
Published: February 2020

3D printed bipolar plate for water electrolysis

Gaoqiang Yang1, Jingke Mo1, Zhenye Kang[1], Frederick A. List III2, Johney B. Green Jr3, Sudarsanam S. Babu2,4, Feng-Yuan Zhang*1

Abstract

A proton exchange membrane electrolyzer is considered as a potential route to the hydrogen production in recent years. It offers a series of advantages, including high product purity, high working current and pressure. As a novel solution for manufacturing process, 3D printing technology is capable of fast and cost-saving prototyping with complex structure from digital models. By employing 3D printing technology, a stainless-steel (SS) component, which is functioned as both of bipolar plate and current distributor, was rapidly produced with selective laser melting (SLM) technique, and was then comprehensively investigated in a proton exchange membrane electrolyzer cell (PEMEC). The experimental results indicated the PEMEC with an 3D printed stainless steel bipolar plate provided an excellent performance, which reached 1.78 V at 2.0 A/cm2 and 80 °C. Furthermore, the 3D printed SS cathode bipolar plate was also ex-situ characterized before and after test by SEM and EDS. This research of 3D printed stainless steel bipolar plate not only provides a route to the quick development of light weight and cheap electrolyzer, but also lead to improvements for other energy related devices.

[1] Nano HELP, Department of Mechanical, Aerospace & Biomedical Engineering, UT Space Institute, University of Tennessee, Knoxville, USA.

2 Oak Ridge National Lab, USA

3 National Renewable Energy Laboratory

* Contacting Author: E-mail: fzhang@utk.edu; Tel: +1-(931)-393-7428
(Invited) Photoelectrochemical Investigation of Rate Limiting Processes and Mechanistic Understanding of Solar Water Oxidation with CuWO4 Photoanodes
Authors: Hamann Thomas
Published: February 2020

Copper tungstate (CuWO4) is a promising material for solar water oxidation that has received limited attention, with many fundamental processes which control the efficiency of water oxidation not fully elucidated. In order to address this, we developed a modified atomic layer deposition method to prepare CuWO4 thin film electrodes for photoelectrochemical (PEC) water oxidation. Application of a suite of systematic PEC measurements were applied to reveal several interesting aspects of this promising material. The hole collection length was quantified by studying the current density-voltage (J-V) behavior and via comparisons of the incident-photon-to-current efficiencies (IPCE) for electrodes with different thicknesses. The CuWO4 thin film electrodes show severe recombination in its depletion region so that the charge separation is limited by the drift length of holes. We will also show that use of H2O2 as a hole scavenger is problematic as it gives rise to current doubling with CuWO4. Sulfite was found to be an ideal hole scavenger which was employed to quantify the hole collection efficiency of water oxidation at the CuWO4 surface. This was compared with results of intensity-modulated photocurrent spectroscopy (IMPS) measurements which showed essentially quantitative hole collection efficiency at 1.23 V vs RHE. The photocurrent onset of water oxidation is shifted about 200 mV positive compared with sulfite oxidation, suggesting surface recombination still limits the water oxidation performance somewhat. Electrochemical impedance spectroscopy (EIS) measurements were employed to understand the role of surface states of CuWO4 which indicated the surface state is not a permanent state in the electronic structure of CuWO4 as proposed by previous literature, but a photogenerated water oxidation intermediate. These combined results will be compared to other well-studied materials, such as hematite, and general operational principles discussed.
(Invited) Advancing Design and Discovery of New Materials for Solar Energy Conversion
Authors: Cooper Jason K. , Jiang Chang-Ming , Sharp Ian D.
Published: February 2020

The development and advancement of new materials for solar-driven chemistry is an area of focused attention because there remains no material that meets the demanding criteria for semiconductor solar photoelectrochemistry, which include stability, efficiency, and scalability. Modern techniques of materials discovery, such as high throughput synthesis and computational screening methods, have proved effective at identifying new classes of materials. However, these materials will require efficient and comprehensive characterization to expose their underlying physics, governed by their electronic structure and native defects. Through utilization of BiVO4 as a testbed, we have developed a scalable synthetic method and a series of characterization tools to elucidate its underlying optical and electronic properties, as well as to mitigate photocarrier recombination at native defects and improve doping. These methods have since been applied to copper vanadate, an n-type semiconductor that has been newly identified as a candidate for use in photoelectrochemical energy conversion, to examine its apparent low performance efficiency.
(Invited) Novel Chalcopyrite Materials for Economical Photoelectrochemical Hydrogen Production
Authors: Gaillard Nicolas , DeAngelis Alexander D , Horsley Kimberly
Published: February 2020

Photoelectrochemistry (PEC) is theoretically one of the most efficient methods to produce alternative fuels, although the efficiency, cost, and durability of lab-scale systems are currently not at the level required to make this technology economically feasible. The chalcopyrite material class provides exceptional candidates to meet the requirements for cheap, sustainable solar fuels production. As we have previously reported, co-evaporated 1.7 eV CuGaSe2 offers very high-saturated photocurrent densities (>15 mA.cm-­2) and high Faradaic efficiency (>85%). However, CuGaSe2 photocathodes suffer from non-ideal surface energetics, requiring additional PV cells to drive the water splitting process. The hybrid photo-electrode (HPE) device, in which a PEC electrode is placed on top of a solar cell, is by far the most efficient approach for unbiased solar water splitting. Unfortunately, CuGaSe2’s narrow bandgap prohibits this integration scheme.

In the present communication, we report on our efforts to synthesize 1.8-2.2 eV band-gap chalcopyrite materials for PEC water splitting. Specifically, we investigated the effect of sulfur on the optical and photoelectrochemical characteristics of the copper chalcopyrite material class. Using co-evaporated 1 μm-thick CuGaSe2 as a baseline system, we demonstrate that the substitution of selenium with sulfur can be accomplished through a simple annealing step. As a result, a dramatic change in optical properties was observed, with a bandgap increase from 1.6 eV (CuGaSe2) to 2.4 eV (CuGaS2). Then, by simply adjusting the indium content during the initial growth process, the bandgap of sulfurized copper chalcopyrite was decreased from 2.4 eV to 2.0 eV. X-ray diffraction data indicated successful bulk sulfurization by the shift of the prominent (112), (220), and (312) reflections to higher angles. Saturated photocurrent densities of 5 mA/cm2 were achieved with 2.0 eV red CuIn0.3Ga0.7S2 photocathodes in 0.5M H2SO4 under AM1.5G simulated illumination. From this proof of concept experiment, we have further developed new synthesis approaches and innovative characterization protocols to achieve PV-grade wide bandgap sulfide-based chalcopyrites capable of generating photocurrent densities over 10 mA.cm-2.
(Invited) Photo-Induced Force Mapping of Plasmonic Nanostructures
Authors: Thomann Isabell
Published: February 2020

Plasmonic nanoparticles serve as efficient optical nanoantennae that interact with light with an effective cross section exceeding their geometric size. We have recently exploited this antenna effect to engineer photoelectrodes for solar water splitting, optimizing for different plasmonic decay mechanisms such as near-field energy transfer to the surrounding semiconductor [1], plasmon-induced hot carrier generation and utilization [2], and broadband extreme light absorption within monolayer MoS2 [3]. However, often more than one plasmonic decay mechanism is at work, which makes it challenging to separate out the relative contributions and optimize them efficiently for solar water splitting. Novel characterization tools to study the heterogeneity of plasmonic photocatalysts both in terms of their morphology and optical near-field enhancements in-situ are therefore of widespread interest. Here we introduce a novel technique called photo-induced force microscopy that allows for simultaneous imaging of topographical features and spectroscopic characterization of near-field distributions with high spectral selectivity and temporal resolution. In this technique, a nanoscale tip is brought in the vicinity of the sample, which is optically excited. The photo-induced gradient forces between the tip and the sample can be detected with nanometer-scale spatial resolution, along with topographical information in atomic force microscopy tapping mode. I will show examples of our combined experimental-theoretical study [4] where we map force intensity enhancements in nanostructures and compare them to simulated force intensity enhancements in which a realistic tip-sample geometry is modeled using Maxwell-Stress tensor methods. Near-field inhomogenities with a spatial resolution less than 10 nm are easily resolved. As such, photo-induced force microscopy will be a welcome addition to the toolbox of nanoscale characterization methods, and will find additional useful applications for the characterization of precisely manufactured nanostructures and surface-enhanced Raman scattering (SERS) substrates. Time permitting, I will discuss charge carrier dynamics in hybrid nanoparticles composed of plasmonic / two-dimensional materials, and applications of photo-induced force microscopy to these study photocatalytic processes.

[1] Nano Letters 2011, 11, p 3440

[2] Nano Letters 2015, 15 (9), p 6155; Chemistry of Materials 2016, 28 (13), p 4546

[3] ACS Photonics 2016, 3 (5), p 853

[4] Nano Letters 2016, Articles ASAP (As Soon As Publishable)
(Invited) Observation of Plasmon-Induced Water Oxidation and Reduction Reactions By in-Situ Electrochemical Surface-Enhanced Raman Scattering
Authors: Murakoshi Kei
Published: February 2020

In-situ electrochemical surface-enhanced Raman scattering (EC-SERS) measurement is a powerful tool to investigate characteristic chemical reactions via multi-electron transfer, especially effective under localized plasmon excitation. Au and Ag nanostructured semiconductors show photoelectric effect under the illumination of visible and near-infrared light. It has been suggested that the effect is due to the exciton generations of the metal nanostructure on n- and p-type semiconductors induced by localized surface plasmons resonances. Plasmon active nanostructured semiconductor electrodes enable water oxidation or reduction via multiple holes or electrons transfer. In this work, EC-SERS from the intermediate species at water oxidation and reduction process at the electrode-electrolyte interface under near-infrared light illumination.
(Invited) High Performance Components for Solar-Driven Photoelectrochemical Fuel Generators
Authors: Houle Frances A
Published: February 2020

The use of sunlight to synthesize useful chemicals such as H2 and hydrocarbon fuels from components of air (water and CO2) has progressed rapidly due to the strong international effort to identify materials and device architectures that improve efficiency and stability. The targets are challenging: a solar fuels generation system must return at least as much chemical energy as the total energy required to fabricate and operate it, and last for a decade or more. Success requires addressing corrosion, membranes properties, integrated semiconductor/catalyst systems and performance under natural conditions involving large temperature swings and diurnal operation. In this talk I will describe studies conducted in JCAP directed toward achieving these targets. Considerations for solar water splitting and CO2 reduction systems will be compared.
Bimetallic Au-Cu Nanocatalysts with Enhanced Electrochemical CO2 Conversion Activity
Authors: Kauffman Douglas R. , Alfonso Dominic R , Tafen DeNyago
Published: February 2020

Converting waste CO2 emissions into value added chemicals and fuels is one approach to mitigating greenhouse gases and reducing the carbon footprint of fossil-fuel processes. The electrochemical CO2 reduction reaction (CO2RR) is a promising carbon mitigation strategy because it can operate at high reaction rates and excellent efficiency at ambient conditions using environmentally friendly aqueous electrolytes. Moreover, the ability to couple carbon-free electricity sources (wind, solar, etc.) enables "carbon neutral" or "carbon negative" technologies that convert CO2into value added products without producing additional emissions.

We’ve combined experimental and computational techniques to characterize the catalytic activity of 2-3 nm, bimetallic gold-copper nanoparticles (NPs) for CO2RR. The catalysts showed composition-dependent CO2RR activity that exceeded both the parent gold and copper metals. Interestingly, the bimetallic NPs produced only CO and H2, whereas bulk, polycrystalline copper also produced methane and ethylene. Electrocatalytic activity studies identified 21% Cu NPs as the most active composition with reaction turnover (TOF) frequencies exceeding 60 s-1 and Faradaic Efficiencies approaching 100% FE at -1.0V vs. RHE. The enhanced activity indicates a synergistic effect upon diluting gold atoms in copper. Laboratory and synchrotron-based X-ray spectroscopies were coupled with density functional theory (DFT) to confirm Au-Cu charge transfer within the NPs and identify mixing between near Fermi-level electronic states. We found a strong correlation between the experimentally-determined TOFs and the computationally-predicted binding energy of key reaction products. The superior performance of 21% Cu NPs stemmed from facile desorption of reaction products and extremely weak H binding. This study shows that atomic composition can be used to tune the electronic structure and chemical reactivity of small bimetallic NPs.
CO2 Conversion to Formic Acid in a Three Compartment Cell with Sustainion™ Membranes
Authors: Yang Hongzhou , Kaczur Jerry , Sajjad Syed D. , Masel Richard I
Published: February 2020

Formic acid generated from CO2 has been proposed both as a key intermediate renewable chemical feedstock as well as a potential energy storage chemical media for hydrogen. In this paper, we describe a novel three compartment electrochemical cell configuration with the capability of directly producing a pure formic acid product in the concentration range of 5 – 20 wt% at high current densities and Faradaic yields. The electrochemical cell employs a Dioxide Materials Sustainion™ anion membrane, allowing for the improved CO2 electrochemical reduction performance. Stable electrochemical cell performance for more than 500 hours has been experimentally demonstrated.

Figure 1 shows the current produced as a function of the cell voltage in a cell with a tin cathode, and IrO2 anode, and deionized water in the middle compartment with no electrolyte added to the water. Notice that one can obtain up to 200 mA/cm² at reasonable cell voltages.

Figure 2 shows how the exit concentration and Faradaic efficiency varies with flowrate. Experimentally, as the Faradaic efficiency decreases as the formic acid concentration rises. Physically, the some of the formic acid is transported to the anode, where it is oxidized leading to formic acid loss. The use of thicker and/or higher MW PSA cation membranes significantly reduces these formate losses.

Figure 3 shows a steady state run. In this case, we are able to maintain an output concentration of 15% formic acid for 500 hours, with no significant change in cell voltage.

Figure 1
Insights in the Catalytic Product Selectivity Trends of Single Site Transition Metal-Nitrogen-Doped Carbons during the Electrochemical Reduction of CO2 to CO
Authors: Ju Wen , Bagger Alexander , Hao Guangping , Varela Ana Sofia , Sinev Ilya , Roldan Beatriz , Kaskel Stefan , Rossmeisl Jan , Strasser Peter
Published: February 2020

The direct electrochemical reduction of CO2 to fuels and chemicals using renewable electricity has attracted much attention in part due to the fundamental surface catalytic challenges related to activity and selectivity, in part owing to its potential practical importance in CO2 valorization for energy and chemicals application.1 In particular, the selective 2-electron reduction to CO has captivated chemists’ and engineers’ minds for the design of technological CO2-consuming cathodes (CCCs) for use as counter electrodes in the polymer-chloralkaline industries, where fossil-based CO currently still serve as feedstock for production of e.g. polycarbonate and polyurethanes. Work on solid catalysts for the selective electrochemical reduction of CO2 to CO has been limited to the traditional noble metal catalysts such as Ag and Au.2 Here, we present new advances in our understanding of the CO2 reduction process on N-coordinated, non-noble metal-doped nano-porous carbons (M-N-C, M=Mn, Fe, Co, Ni, Cu). These materials are single site catalysts comprising active M-Nx moieties. We investigate the trends in their intrinsic electrochemical reactivity, CO turnover frequencies, and CO efficiencies and show that Fe-N-C and Ni-N-C catalysts outperform Au or Ag. We model the active site by Density Functional Theory (DFT) and arrive at a consistent atomic-scale understanding of their potential-dependent CO and hydrocarbon selectivity. Linking DFT predictions directly with experiments we explain why Fe-N-C and Ni-N-C represent the most cost-effective and energy-efficient carbon-based catalysts for future CO generation inside CCCs.

References:

1 Huei-Ru “Molly” Jhong, S. M., Paul JA Kenis. Electrochemical conversion of CO2 to useful chemicals: current status, remaining challenges, and future opportunities. Current Opinion in Chemical Engineering
2, 191-199 (2013).

2 AS Varela, N. S., J Steinberg, W Ju, HS Oh, P Strasser. Metal-Doped Nitrogenated Carbon as an Efficient Catalyst for Direct CO2 Electroreduction to CO and Hydrocarbons. Angew. Chem. Int. Ed.
54, 10758–10762 (2015).
CO2 Conversion Via Nanoporous PS-PVP Block Copolymer: Revisiting the Pyridyl Radical
Authors: Ghebremichael Habte , Sidorenko Alexander
Published: February 2020

The threat of climate change proves to be one of mankind’s most daunting challenges. Carbon dioxide emissions are believed to be a leading contributor to climate change. The development of nontoxic and abundant catalysts for the reduction of CO2 is critical in enabling this much needed technology. A method of reverse combustion would be prove to be advantageous in mitigating climate change and providing for a carbon neutral fuel source. Pyridine has shown to be electrocatalytically active at reducing carbon dioxide at low overpotentials to hydrocarbons.The development of nanoporous polymer thin films have exhibited many useful properties that have yet to be exploited. Taking advantage of the microphase separation phenomenon of poly(styrene)-poly(4-vinylpyridine), PS-P4VP, block copolymers allows for pyridine moieties to assemble onto the cylindrical interior of these nanoporous surfaces. These moieties we've shown to be both electrocatalytically active in conjunction with conductive co-catalyst via a radical mechanism.