Cell Performance Loss Research Articles

Electrochemical Performance of Lithium-Ion Cells with Lithium- and Manganese- Rich Oxide Cathodes

State-of the-art (SOA) lithium-ion batteries (LIBs) being developed for transportation applications contain a transition metal (TM) oxide cathode and a graphite anode; both serve as host-matrices to house lithium ions during battery operation. The cathodes typically contains Li1+xNiaCobAlcO2 (NCA) or Li1+xNiaMnbCocO2 (NMC) oxides: both oxide chemistries contain Co, which is known to preserve the layered structure during lithium extraction/insertion reactions. However, the possibility of a global Co shortage and soaring costs has galvanized the LIB community to explore sustainable cathode chemistries, while maintaining cell performance (energy/power densities), safety and cycle/calendar life. In this context the U.S. Department of Energy (DOE) initiated the Earth-Abundant Cathode Active Material (EaCAM) Program for the development of sustainable cathode chemistries, based on earth-abundant elements.Materials of particular interest to the EaCAM program are the x Li2MnO3 ● (1-x) LiMnaNibZcO2 composites; here Z refers to various elements that could be included in the oxide structure. These lithium- and manganese- rich materials are considered attractive candidates because of their high specific capacities, zero cobalt content, and lower costs compared to the SOA oxides. We have been examining the electrochemical behavior of cells with these oxides, with a particular focus on the 0.3 Li2MnO3 ● 0.7 LiMn0.5Ni0.5O2 (LMR) compound.During this presentation, we will show results from battery cells, containing LMR cathodes and either graphite or lithium-titanate anodes. In particular, the use of a microprobe reference electrode to monitor the cathode and anode potentials will be discussed. The effect of activation on cell performance and the performance loss characteristics during cycling will be highlighted. We will show how cell impedance is affected by voltage hysteresis and the voltage fade that results from cycling. Our ultimate goal is to identify constituents and mechanisms responsible for the cell performance loss and develop solutions to mitigate this degradation.Acknowledgement: This document has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357.

A scale-bridging model for proton exchange membrane fuel cells: Understanding interactions among multi-physics transports, electrochemical reactions and heterogeneous aging

The lifetime issues caused by catalyst degradation is one of the most critical challenges for the commercial application of proton exchange membrane fuel cells. However, the understanding concerning the interactions among transport, reaction, and catalyst degradation is inadequate for further durability enhancement. Herein, a scale-bridging model that couples a cell-scaled model to reveal the reactive transport process and a catalyst-scaled model to unveil Pt degradation is proposed to capture the degradation characteristics. It is found that the heterogeneous aging is observed in both the through-plane and channel-rib directions due to the enhanced mass loss near the membrane and the water accumulation under the rib, resulting in the mitigation of the core reaction region away from the membrane, thereby causing an increase in ohmic loss after cycles. More importantly, the local oxygen transport resistance increases with degradation, leading to a remarkable cell performance loss under high current density. Additionally, the influences of cell voltage load and inlet humidity on Pt degradation are also investigated. And the proposed gradient catalyst layer shows a significant mitigating effect on Pt degradation. This work reveals the degradation-performance interactions, which is conducive to design the high-performance fuel cell to prolong lifetime.

Understanding Charge, Mass, and Heat Transfer in Fuel Cells for Transport Applications – Insights from the Camelot Project

Proton Exchange Membrane Fuel Cells (PEMFCs) are a promising solution for zero-emission vehicle propulsion owing to their high energy density, low operating temperature, and high efficiency. The overall aim of the CAMELOT project is to improve the power density of fuel cells by understanding the limitations on the performance of state-of-the-art (SoA) and beyond SoA PEMFC membrane electrode assemblies (MEAs). To achieve this, the CAMELOT project has diagnosed the fundamental transport properties that limit performance of these MEAs and materials. Not only has the CAMELOT project produced MEAs with features that have the potential to enable disruptive performance increases but have further developed leading open-source models to enable accurate simulations validated through experimental work. In-depth parametrisation of fuel cell components through extensive ex-situ and in-situ characterisation has been performed to provide input to the modelling activities. The two major modelling advances achieved by the CAMELOT project are i) the improvement of water uptake and transport models, especially concerning ultra-thin PEMs, and ii) extending a leading open-source model (FAST-FC) to enable accurate simulation of beyond SoA fuel cell performance and voltage loss breakdown. CAMELOT has developed a series of beyond-SoA fuel cell components to ensure that the modelling inputs are representative of SoA component properties. A series of membranes with varying thicknesses were prepared and a range of ex-situ experiments were carried out to gather water uptake and permeability properties for the water transport models. Additional in-situ electrochemical characterisation was carried out on a series of catalyst coated membranes (CCMs) to extract important properties of the catalyst and membrane components as inputs to improve the physics-based fuel cell performance model.Significant results from the project to be highlighted in this presentation include the development of a water transport model with improved description of water uptake and transport in thin ionomeric layers, the development of a predictive modelling framework from which we can identify the most important material parameters to tune to reach our MEA performance targets of 2.7 A/cm2 at >0.67 V with total catalyst loadings <0.08 mgPt/cm2, the development of ultrathin (< 10 µm) proton exchange membranes and ultra-low loading cathode catalyst loadings (0.08 mgPt/cm2), the development of catalyst coated membranes (CCMs) with in-plane catalyst and ionomer gradients, and extensive in-situ fuel cell characterization of the SoA CAMELOT CCMs/MEAs.The CAMELOT project has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking (now Clean Hydrogen Partnership) under grant agreement No 875155. This Joint Undertaking receives support from the European Union’s Horizon 2020 Research and Innovation program, Hydrogen Europe and Hydrogen Europe Research.

Cathode Loading Impact on PEM Fuel Cell Performance Losses in Voltage Cycling Based Accelerated Stress Tests

In order to reach the target of carbon neutrality by the end of 2050 set by the European Union, hydrogen technologies will play an important role in supporting the transition to a renewable energy economy, especially for heavy duty applications, such as trucks and airplanes.1 For the latter, hydrogen is a viable alternative fuel compared to kerosene, offering a higher specific energy density as well as zero in-flight CO2 emissions.2 However during operation, proton exchange membrane fuel cells (PEMFCs) suffer from significant performance losses due to the instability of Pt-based catalysts for the oxygen reduction reaction (ORR) via the loss of electrochemically active surface area (ECSA).3 This induces substantial decay in the H2/air performance mainly due to the increasing impact of the local O2 transport resistance (RO2,local) with decreasing cathode roughness factor (rf, in units of cm2 Pt cm-2 MEA), which is especially pronounced for low Pt-loadings.4 Thus, for heavy duty applications requiring long-term durability, higher Pt loadings are required to reduce the impact of RO2,local.In this study, we analyse the H2/air performance loss contributions during voltage cycling based accelerated stress tests (ASTs) using cathodes with different Pt-loadings. ASTs were performed using 5 cm2 MEAs with cathode Pt loadings of 0.2, 0.4, and 0.8 mgPt cmMEA -2 (48.6 wt%, TEC10V50E, Tanaka Kikinzoku K.K. (TKK)). Full characterization of the MEA performance characteristics after different numbers of voltage cycles, was performed by measuring: i) H2/O2 and H2/air polarization curves; ii) cathode rf, determined by cyclic voltammetry and CO stripping; iii) O2 transport resistances (RO2,total) via limiting current measurements; and, iv) proton conduction resistances in the cathode catalyst layer (RH+,cath) via electrochemical impedance spectroscopy (EIS). Voltage cycling was performed under H2/N2 (200/75 nccm) at 80 °C, 95% RH, and ambient pressure using square wave profiles with lower and upper potential limits of 0.60 and 0.95 V, respectively, with hold times of 1 s at each potential.A strong H2/air performance dependency on the cathode rf is visible for the same Pt/C cathode catalyst with varying Pt loading. As shown in Figure 1, the same H2/air performance is reached at similar cathode rf values, independent of number of voltage cycles. This is due to the observation that the RO2,local values only depend on the cathode rf and not on the electrode’s history.Finally, when choosing an end-of-life (EoL) criterion of a more than 20 mV deviation of the measured cell voltages at a given current density from the theoretical ORR kinetics losses (c.f. red line in Figure 1 and gray areas for accepted cell voltage range), this EoL criterion is reached for the differently loaded MEAs at the same cathode rf but after different amounts of aging cycles. For example, at 1.5 A cm2 MEA this 20 mV deviation is reached at a cathode rf of 50-70 mgPt 2 cmMEA -2. However, for the 0.8 mgPt cmMEA -2 Pt/C cathode more than 200.000 cycles are needed to reach this value, compared to only 5.000 cycles for the 0.2 mgPt cmMEA -2 loaded cathode. Consequently, a 4-fold increase of the the cathode Pt loading increases its voltage cycling stability by »40-fold.

Revealing the accelerated crack prolongation behavior under chemical ionomer degradation within the catalyst layer

As a critical electrochemical reaction region of the proton exchange membrane fuel cell (PEMFC), the cracking issue of the catalyst layer (CL) considerably affects the performance and durability of the PEMFC. However, the impact of chemical ionomer degradation on CL cracking has not been comprehensively revealed. This study investigates the effect of chemical ionomer degradation on CL cracking through accelerated stress tests, characterization, and theoretical analysis. The results indicate that the increasing chemical degradation degree facilitates CL cracking. The CL with the most severe chemical degradation has a single total crack length increment of 1.97 times for the novel CL under the same degree of mechanical degradation. CL fracture resistance analyses reveal that the decrease in interface fracture resistance is the predominant impulse in accelerating CL cracking. Furthermore, the cell voltage reduction of the CL with the most severe chemical degradation during mechanical degradation is 34.22 mV at the current density of 1800 mA cm−2, which is 1.82 times for the fresh CL. The increment of activation resistance and mass transfer resistance are the main causes of the larger cell performance loss. The above findings emphasize the significance of high interface fracture resistance in inhibiting CL cracking and offer theoretical support for analyzing post-operational CL cracking.

Long-Term Tests and Advanced Post-Test Characterizations of the Oxygen Electrode in Solid Oxide Electrolysis Cells

Solid Oxide cells (SOCs) are promising high-temperature electrochemical energy-conversion devices, which enable a fossil-free sustainable development. Nevertheless, performance degradation is still a bottleneck for the large-scale commercialization. The most commonly employed material for the air electrode is La1-xSrxCoy-1FeyO3-δ. The chemical decomposition of this material is known to considerably impact the cell performance [1,2].The studied cells are composed of a La0.6Sr0.4Co0.2Fe0.8O3 -δ (LSCF) current collecting layer (CCL) and a LSCF-Ce0.8Gd0.2O2 -δ (LSCF-GDC) composite for the air electrode, GDC for the barrier layer, (Y2O3)0.08(ZrO2)0.92 (YSZ) for the electrolyte and Ni-YSZ for the functional layer and the support layer of the fuel electrode. The present study aims to investigate the degradation occurring in the air electrode of a complete cell aged at 750°C for 2000 h in electrolysis mode. The cell degradation is assessed by electrochemical measurements, such as polarization curves and electrochemical impedance spectroscopy (EIS), and post-mortem characterizations of the air electrode using high resolution multimodal chemical imaging based on synchrotron X-ray diffraction (µ-XRD) in Paul Scherrer Institut (PSI, microXAS), complemented by X-ray photoelectron spectroscopy (XPS).The electrochemical characterizations performed at the beginning of the test and after ageing showed a decrease in the cell performance. Notably, a significant evolution at the high frequency region was observed in the impedance spectrum. However, the medium frequency region of the EIS, mainly ascribed to the air electrode using a physically-based multiscale model [3], did not show any particular evolution. Post-mortem characterizations using synchrotron µ-XRD technique showed an inter-diffusion layer (IDL) in between the GDC and YSZ layers, for both pristine and aged samples (Fig. 1). In addition, a slight increase in the LSCF unit cell volume was observed after ageing. Nevertheless, XPS results did not highlight any significant evolution in the Sr segregation after operation. According to the impedance spectra and the post-mortem analyses, the ageing of the air electrode seems to have a limited impact on the cell performance loss in these operating conditions.

Three-dimensional nanoimaging of fuel cell catalyst layers

Catalyst layers in proton exchange membrane fuel cells consist of platinum-group-metal nanocatalysts supported on carbon aggregates, forming a porous structure through which an ionomer network percolates. The local structural character of these heterogeneous assemblies is directly linked to the mass-transport resistances and subsequent cell performance losses; its three-dimensional visualization is therefore of interest. Herein we implement deep-learning-aided cryogenic transmission electron tomography for image restoration, and we quantitatively investigate the full morphology of various catalyst layers at the local-reaction-site scale. The analysis enables computation of metrics such as the ionomer morphology, coverage and homogeneity, location of platinum on the carbon supports, and platinum accessibility to the ionomer network, with the results directly compared and validated with experimental measurements. We expect that our findings and methodology for evaluating catalyst layer architectures will contribute towards linking the morphology to transport properties and overall fuel cell performance.

Photochemical Decomposition of Y‐Series Non‐Fullerene Acceptors Is Responsible for Degradation of High‐Efficiency Organic Solar Cells

AbstractOrganic photovoltaic cells that employ Y‐series non‐fullerene acceptors (NFAs) have recently achieved impressive power‐conversion efficiencies (&gt;18%). To fulfill their commercial promise, it is important to quantify their operational lifetimes and understand their degradation mechanisms. In this work, the spectral‐dependent photostability of films and solar cells comprising several Y‐series acceptors and the donor polymer PM6 is investigated systematically. By applying longpass filters during aging, it is shown that UV/near‐UV photons are responsible for the photochemical decomposition of Y‐series acceptors; this degradation is the primary driver of early solar cell performance losses. Using mass spectrometry, the vinylene linkage between the core and electron‐accepting moieties of Y‐series acceptors is identified as the weak point susceptible to cleavage under UV‐illumination. Employing a series of device characterization, along with numerical simulations, the efficiency losses in organic photovoltaic cells are attributed to the formation of traps, which reduces charge extraction efficiency and facilitates non‐radiative recombination as the Y‐series acceptors degrade. This study provides new insights for molecular degradation of organic photovoltaic absorber materials and highlights the importance of future molecular design and strategies for improved solar cell stability.

Impact of Catalyst Reconstruction on the Durability of Anion Exchange Membrane Water Electrolysis

Anion exchange membrane water electrolysis (AEMWE) offers an opportunity to use inexpensive nonprecious metal catalysts. However, pure water-fed AEMWE still faces issues of durability. Herein, we compared the stability of AEMWE under different anolytes, including KOH, pure water, and a phosphate buffer (PB) using a NiFeCo oxygen evolution reaction catalyst. Upon thoroughly characterizing several changes before/after 100 h durability tests, such as the cell performance, catalyst dissolution, catalyst morphologies, impedance of the anion exchange membrane, and catalytic layer, we speculate that the change of the local pH is the main factor causing catalyst reconstruction, which further leads to the loss of cell performance in the pure water-fed mode. By using PB to control the local pH, the morphology of the catalyst will no longer change after the durability test, and the cell performance can recover to the initial performance in pure water. These results not only indicate that the catalyst structural transformation is the main reason for the deactivation of pure water-fed AEMWE but also help find a way to achieve highly durable pure water-fed AEMWE.

In-situ preparation of low Pt loading multi rhombic-pyramidal Pt–Pd catalyst layer for high-performance proton exchange membrane fuel cells

The catalyst layer (CL) is the only electrochemical reaction site in proton exchange membrane fuel cells (PEMFCs), decisive in their performance. Herein, a mild and simplified strategy is implemented into the in-situ growth of Pt–Pd alloy catalysts on the gas diffusion layer (GDL) as the CLs for PEMFCs. Pt/C is used as the nucleation site to assist the in-situ growth of the Pt–Pd CL. The as-prepared Pt–Pd CL behaves as a multi rhombic-pyramidal structure, which are evenly distributed on the GDL surface. The effect of the Pt/Pd atomic ratio on the electrocatalytic activity is investigated through a single-cell performance test, and the optimal atomic ratio is determined to be 1/2, which exhibits excellent cell performance and low activation polarization loss. Meanwhile, the single-cell test results reveal that Pt1Pd2 CL reaches optimal performance at a loading of 0.122 mg cm−2 (∼0.06 mgPt cm−2), with a peak Pt-specific power density of 14.23 W mg−1 (6.81 W mg−1 in PtPd), approximately 3.96 times that of a commercial Pt/C CL (0.2 mgPt cm−2). Furthermore, Pt1Pd2 CL shows significantly better stability than the commercial Pt/C CL, indicating that the in-situ preparation of the Pt-based CL has an excellent prospect for the commercial development of PEMFCs.

Anode Catalyst Durability and Accelerated Stress Tests in Proton Exchange Membrane-Based Low Temperature Electrolysis

Hydrogen has unique advantages as an energy carrier, with a high energy density and abilities for long term storage and conversion between electricity and chemical bonds. Although hydrogen currently has a significant role in transportation and agriculture, its use in energy consumption overall has been limited, particularly in the case of electrochemical water splitting. With decreasing electricity prices, electrolysis cost reductions can be achieved and allow for an opportunity for greater use.(1) While load-following renewable power sources can reduce feedstock cost, further cost reductions can be achieved by reducing the platinum group metal (PGM) content.(2) Efforts are needed to understand and mitigate electrolyzer degradation, particularly when accounting for lower PGM loadings and intermittent operation.In this presentation, studies related to anode catalyst durability will be discussed and include the impact of individual stressors, observed degradation mechanisms, and the development of catalyst-specific accelerated stress tests. Membrane thickness and ohmic losses were deconvoluted from catalyst layer durability experiments, allowing for a transition from potential-driven parametric observations to current-driven stress tests for advanced materials and coating processes. Expanded studies have incorporated advanced materials, including higher surface areas, different oxide compositions, supports, and multicomponents. Kinetic improvements were found to lessen load requirements and can mitigate catalyst loss. Cell performance loss during extended operation, however, tended to qualitatively correspond to ex-situ dissolution rates and less stable materials accelerated catalyst layer thinning, migration into the membrane, and interfacial tearing. Perspectives on anode catalyst development will be discussed and increasing site-access and utilization further into the catalyst layer is needed to better understand the role of advancements in mitigating electrolyzer durability losses.[1] B. Pivovar, N. Rustagi and S. Satyapal, The Electrochemical Society Interface, 27, 47 (2018).[2] K. Ayers, N. Danilovic, R. Ouimet, M. Carmo, B. Pivovar and M. Bornstein, Annual Review of Chemical and Biomolecular Engineering, 10, 219 (2019).[3] Electron microscopy was performed at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.

Temperature-Dependent Carrier Extraction and the Effects of Excitons on Emission and Photovoltaic Performance in Cs0.05FA0.79MA0.16Pb(I0.83Br0.17)3 Solar Cells.

The photovoltaic parameters of triple cation perovskite [Cs0.05FA0.79MA0.16Pb(I0.83Br0.17)3] solar cells are investigated focusing on the electro-optical properties and differences in performance at low and high temperatures. The signature of a parasitic barrier to carrier extraction is observed at low temperatures, which results in a loss of performance at T < 200 K. Intensity-dependent measurements indicate extraction across this parasitic interface is limited by a combination of the exciton binding energy and thermionic emission. However, the photovoltaic performance of the device is recovered at low intensity─where the photocarrier generation rate threshold is lower than the thermionic extraction rate. Loss of solar cell performance is also observed to be strongly correlated to an increase in photoluminescence intensity, indicating inhibited carrier extraction results in strong radiative recombination and that these systems do not appear to be limited by significant thermally activated non-radiative processes. Evidence of limited carrier extraction due to excitonic effects is also observed with a strong anti-correlation in photoluminescence and carrier extraction observed at lower temperatures.

(Invited, Digital Presentation) Impedance Analysis of Porous Electrodes in Solid Oxide and Polymer Electrolyte Fuel Cells

Technical electrodes in fuel cells rely on complex multiphase microstructures that facilitate electronic, ionic and gas transport to active reaction sites distributed in the electrode volume. In such electrodes, material and microstructural properties of the porous electrode likewise determine the cell performance and different losses related to gas diffusion, electronic / ionic transport or the charge transfer at the active reaction sites might dominate the electrode resistance.Impedance spectroscopy is a powerful tool to evaluate and quantify the losses within a porous electrode. In this contribution it will be shown how impedance spectroscopy, an impedance data analysis by the distribution of relaxation times (DRT) (1,2) and a subsequent transmission line modeling (TLM) can provide physicochemically meaningful information about technical electrodes applied in solid oxide cells (SOC) (3-7) and polymer electrolyte fuel cells (PEFC) (4,5). Limitations in TLM will be discussed and it will be shown that the well-established straight-forward approach of CNLS-fitting might lead to physicochemically incorrect results. Possible countermeasures as a pre-identification of TLM-parameters by means of separate electrical measurements and microstructural analysis or an appropriate selection of operating parameters during impedance analysis will be presented.An example for the application of TLM in electrode development and microstructural design of the multiphase microstructure will be discussed and examples how the TLM-approach can be used to optimize an electrode in consideration of available materials and producible microstructures will be shown.(1) S. Dierickx, A. Weber and E. Ivers-Tiffée, Electrochim Acta, 355, p. 136764 (2020).(2) A. Weber, tm - Technisches Messen, 88 (1), p. 1 (2021).(3) C. Endler-Schuck, J. Joos, C. Niedrig, A. Weber and E. Ivers-Tiffée, Solid State Ionics, 269, p. 67 (2015).(4) M. Heinzmann, A. Weber and E. Ivers-Tiffée, J. Power Sources, 402, p. 24 (2018).(5) M. Heinzmann, A. Weber and E. Ivers-Tiffée, J. Power Sources, 444, p. 227279 (2019).(6) S. Dierickx, J. Joos, A. Weber and E. Ivers-Tiffée, Electrochim Acta, 265, p. 736 (2018).(7) S. Dierickx, T. Mundloch, A. Weber and E. Ivers-Tiffée, J. Power Sources, 415, p. 69 (2019).

Influence of Shell Thickness on Durability of Ru@Pt Core-Shell Catalysts for Reformate PEM Fuel Cells

For the use of polymer electrolyte membrane fuel cells (PEMFCs) in heavy duty applications, on-site generation of hydrogen rich gas by reforming hydrocarbons or methanol are a suitable alternative to pure H2 due to higher availability and higher energy density of hydrocarbon fuels [1]. The so-called reformate contains in addition of H2 also CO, which is a catalyst poison. PtRu alloys are the most promising catalysts for PEM fuel cells operated with reformate due to their high CO-tolerance [2]. It is known that the less noble Ru is unstable in acidic PEMFC conditions and is lowering the durability of the membrane electrode assembly (MEA) by dissolution and crossing over through the membrane to the cathode [3]. Ru dissolution and crossover result in a decreased CO-tolerance on the anode and a lower activity of the cathode towards oxygen reduction due to Ru blocking the Pt surface of the cathode catalyst [4]. To prolong the lifetime and CO-tolerance of reformate PEMFCs, the stability of the anode catalysts must be improved. One approach is nano-structuring the catalysts by encapsulating the less noble Ru-core with a Pt-shell. In doing so, the corrosion resistant Pt-shell supposes to protect the Ru-core from dissolution and thus mitigates the Ru crossover phenomenon.In this work, the influence of the Pt-shell thickness on the stability and performance of the Ru@Pt catalysts is investigated. Two catalysts with varying Pt-shell thicknesses were synthesized on Vulcan XC72R carbon via a two-step polyol. The catalyst with the thinner Pt-shell is called Ru@1Pt and with the thicker shell Ru@2Pt. The as-synthesized catalysts were physically characterized by XRD, ICP-OES, TEM and EDS. A representative EDS map of Ru@1Pt is shown in fig. 1a. The physical characterization of the obtained catalysts unveils a Ru@Pt core-shell structure with crystalline hcp Ru and fcc Pt. To further investigate the catalysts electrochemically, MEAs were manufactured using Ru@Pt catalysts as anodes and commercial membranes and cathode catalysts. An accelerated stress test (AST) was developed to target Ru dissolution by potential cycling and was applied to investigate and compare the stability of the catalysts. The MEAs were electrochemically characterized by cyclic voltammetry, CO-stripping and U-I curves before, during and after the AST. Post-mortem cross-section STEM analysis of the stressed cells were performed to evaluate the elemental composition and morphology of the anode and cathode after the stress test.During the AST, CO-stripping on the Ru@1Pt anode showed a peak shift to higher potentials, indicating a decrease in CO-tolerance due to Ru loss. By contrast, on the Ru@2Pt anode, the peak shifted to lower potentials implying a stronger promoting influence of Ru. On the cathode side, CV measurements before and after the AST revealed a double layer increase and a decrease in the HUPD. This change implies the poisoning of Pt with Ru and were more pronounced for Ru@1Pt compared to Ru@2Pt. As seen by the CO-stripping and CV results, the Ru dissolution and crossover was more severe for Ru@1Pt than for Ru@2Pt. Hence, a higher fuel cell performance loss was observed for the cell with Ru@1Pt in H2, as can be seen in fig. 1b. In addition, further U-I curves were measured under varying reformate conditions to identify the influence of CO on the cell performance. Cross-section EDS maps of the stressed MEAs were used to evaluate the Ru dissolution and its distribution in the different layers of the MEA. A higher Ru:Pt ratio was found on the cathode for the cell with Ru@1Pt compared to a cell with Ru@2Pt, which further verifies a higher degree of Ru crossover for the catalyst with the thinner Pt-shell. The above findings could evidence that the shell thickness plays a significant role in the corrosion resistance of core-shell reformate anode fuel cell catalysts.

Novel bifunctional fillers (ATP/P–CNOs) for sulfonated poly(aryl ether sulfone) matrix for improved power output and durability of H2/O2 fuel cell at low humidity

The preparation of novel composite proton exchange membranes (PEMs) with homogeneous structures and efficient proton-conducting sites is of great importance for the development of PEM fuel cells. In this work, a double-filler of adenosine triphosphate (ATP) and phosphorylated carbon nano-onions (P–CNOs) is incorporated into sulfonated poly(aryl ether sulfone) (SPAES) by simple solution mixing to design a bionic proton-conduction pathways for high-performance PEMs. A series of uniformly distributed, dense and flexible SPAES/ATP/P–CNOs membranes are prepared and characterized for their membrane morphology, water uptake, dimensional stability, electrochemical properties and durability. Both the ATP and P–CNOs fillers can provide abundant proton conducting sites through hydrogen-bonding networks and acid-base pairs, thus improving the membrane stability and proton conductivity. Thanks to the formation of ionic interaction between ATP/P–CNOs and their interaction with SPAES substrates, the composite membranes demonstrate higher ATP retention, better dimensional-mechanical-chemical stability, higher proton conductivity and power output than the pristine and single-filler SPAES membranes. The SPAES/ATP/P–CNOs-2 membrane displays high proton conductivity (196 mS/cm at 90 °C in water and 33 mS/cm at 80 °C/51% relative humidity, RH) and power output (752 mW/cm2 at 80 °C/100% RH and 302 mW/cm2 at 80 °C/50% RH) in a H2/O2 fuel cell. It also experiences the minimal cell performance loss and lowest hydrogen crossover during 6 days of operation at 60% RH. The proposed ATP/P–CNOs channel approach can provide a reference for the development of multi-component composite high-efficiency PEMs for fuel cells.

All Solid-State Li/LLZO/LCO Battery Enabled by Alumina Interfacial Coating

Li7La3Zr2O12 (LLZO) garnet-type lithium-ion conductors are being investigated as a promising solid electrolyte for solid-state lithium batteries. To enable a functional all-solid-state configuration intensive investigations are needed to reduce the cathode/electrolyte interfacial resistance which contributes the most to cell performance loss. Among the commercial cathode materials investigated so far, LiCoO2 (LCO) is one of the most stable with garnet electrolytes as only a superficial reaction has been detected between the two materials. However, even this minor reaction would block the Li-ion transport through the interface, resulting in deteriorated cell performance. In this work, we demonstrate that a thin aluminum oxide layer (5 nm) can be an effective interlayer to impede the formation of a harmful interphase and enable facile Li-ion transfer between LCO and the LLZO garnet. Room-temperature-sputtered LCO thin films were employed to form an interface with the garnet electrolyte and annealed at 800 °C to reveal the effect of the interfacial reaction on the Li-ion transfer across the interface. An aluminum oxide layer was then introduced between LCO and the garnet electrolyte by sputtering a metallic aluminum layer which is then annealed together with the upper LCO layer in oxygen, or by direct atomic layer deposition of the oxide. Compared to the LCO/LLZO/Li cells without an aluminum oxide interlayer, those with the interlayer exhibited improved performance, i.e., a stable discharge capacity of up to 90 mAh/(g LCO) at a C/10 rate, a rate capability up to 1.68C and a stable galvanostatic cycling at 0.1C for over 100 cycles with a discharge capacity fade rate of 0.15% per cycle. It was determined that aluminum diffused into the LCO layer after preventing the initial detrimental reaction between LCO and the LLZO garnet from happening during high temperature annealing, suggesting that the coating does not have to remain a physically blocking layer during cycling to function.

Glass vs. Backsheet: Deconvoluting the Role of Moisture in Power Loss in Silicon Photovoltaics With Correlated Imaging During Accelerated Testing

Moisture ingress is an established issue for photovoltaic module durability. Durability studies that probe moisture effects typically evaluate performance losses at the module level, attributing global power losses to the overall humidity condition of the test environment while leaving local module behavior unknown. We leverage our recently published water reflectometry detection method and biased photoluminescence imaging to spatially correlate moisture content and cell performance over 2500 h of damp heat testing. These tests, carried out on glass–glass and glass–backsheet mini-modules at multiple temperatures and humidities, reveal two dominant modes of local cell performance loss—acute finger interruptions and cell-wide “background” series resistance increase. Finger interruptions occur earliest in glass–glass modules and at dry conditions. We do not observe any signs of contact corrosion at the front side in either module types. Still, glass–backsheet modules show a unique increase in series resistance at high humidities, suggesting a mechanism at the back contact. Overall, our results point to the humidity level of installation climate as a driving variable in selection of the bottom module layer.

Cell performance and flow losses of proton exchange membrane fuel cells with orientated-type flow channels

Orientated-type flow channels of proton exchange membrane fuel cells having baffles increase the cell performance, however, the higher power loss accounted by baffles, is a non-ignorable disadvantage. Previous literature proves that the baffles in channels cause the increase in power losses, while how the baffles affect the power losses, including the frictional losses and local losses, are still not analyzed before. Therefore, in this paper, a two-dimensional model is developed to study the friction loss and local loss in the flow channels with baffles. The numerical model, which couples the non-Darcy flow effect, is validated by comparing with self-conducted experimental results. Experimental and simulation results reveal that: orientated-type flow channels facilitate enhance the power output, and with the enlargement of baffles, the performance is further enhanced. In addition, the frictional losses and local losses in the orientated-type flow channels are comparatively studied by a numerical approach for the first time. It is found that using the materials with low surface roughness can decrease the friction loss; and avoiding sudden expanded segments at leeward sides of baffles can reduce the local loss. The experimental results and simulation results can further help improve the flow channel design.

Nitrogen-functionalized carbon-supported Pt catalysts implemented in high-temperature polymer electrolyte membrane fuel cell

Nitrogen-modified carbon supports were investigated in the catalyst layer of a high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) with respect to fuel cell performance, kinetic, and transport-related voltage losses. Catalysts with different amounts of nitrogen functional groups (NHx) were synthesized and characterized by elemental analysis, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The interaction between the nitrogen-containing functional groups and the phosphate ions was investigated in RDE experiments. The experiments showed that in the case of the nitrogen-functionalized catalysts, the activity is reduced by a factor of up to 2 compared with a commercial Pt/C catalyst in 0.1 M HClO4 + 0.05 M H3PO4. The interaction was further confirmed by membrane electrode assembly (MEA) testing. Impedance spectra and distribution of relaxation times (DRT) analysis were used to pinpoint the voltage losses of the fuel cell. We show that a low amount of nitrogen-containing functional groups improves performance; this can be attributed to the improved phosphoric acid distribution in the catalyst layer. This method can successfully control the acid distribution but must be fine-tuned for extended cell operation.

(Invited) Catalyst Assessments and Device Incorporation in Low Temperature Electrolysis

Although hydrogen has a significant role in transportation and agriculture, its use in energy consumption overall has been limited, particularly when produced through electrochemical water splitting. With decreasing electricity prices, electrolysis cost reductions can be achieved and allow for an opportunity for greater use.(1) While load following renewable power sources can reduce feedstock cost, further cost reductions rely on minimizing the capital cost by reducing the platinum group metal (PGM) content.(2) Efforts are needed to understand and mitigate electrolyzer degradation, particularly when accounting for lower PGM loadings and intermittent operation.Previous efforts have developed accelerated stress tests focused on catalyst layer and interfacial loss with standard material sets. (3) Expanded studies have incorporated advanced materials, including higher surface areas, different oxide compositions, supports, and multicomponents. Kinetic improvements were found to lessen load requirements and can mitigate catalyst loss. Cell performance loss during extended operation, however, tended to qualitatively correspond to ex-situ dissolution rates and less stable materials accelerated catalyst layer thinning, migration into the membrane, and interfacial tearing.While individual components dictate cell-level performance and durability, how components are integrated into membrane electrode assemblies was found to have an impact on catalyst layer properties and electrolyzer performance/durability. (4) Catalyst layers were modified using an ultrasonic spray approach due to the number of variables that could be tuned. While changes to these variables affect several properties and loss mechanisms, trends were found with regards to how catalyst-ionomer integration and catalyst layer uniformity affected performance nonidealities and how losses grew during extended operation. These approaches are useful in diagnostics, to identify and mitigate lower performance and durability. Understanding catalyst layer formation and the relationship between catalyst layer properties and electrolyzer performance/durability is critical to establishing baselines and better informing catalyst development and fabrication efforts.[1] B. Pivovar, N. Rustagi and S. Satyapal, The Electrochemical Society Interface, 27, 47 (2018).[2] K. Ayers, N. Danilovic, R. Ouimet, M. Carmo, B. Pivovar and M. Bornstein, Annual Review of Chemical and Biomolecular Engineering, 10, 219 (2019).[3] S. M. Alia, S. Stariha and R. L. Borup, J. Electrochem. Soc., 166, F1164 (2019).[4] S.M. Alia, K.S. Reeves, J.S. Baxter, D.A. Cullen, J. Electrochem. Soc., 167, 144512 (2020).