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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Effects of surface chemistry and microstructure of electrolyte on oxygen reduction kinetics of solid oxide fuel cells

In this study, we report systematic investigation of the surface properties of yttria-stabilized zirconia (YSZ) electrolytes with the control of the grain boundary (GB) density at the surface, and its effects on electrochemical activities. The GB density of thin surface layers deposited on single crystal YSZ substrates is controlled by changing the annealing temperature (750-1450 °C). Higher oxygen reduction reactions (ORR) kinetics is observed in samples annealed at lower temperatures. The higher ORR activity is ascribed to the higher GB density at the YSZ surface where 'mobile' oxide ion vacancies are more populated. Meanwhile, oxide ion vacancies concurrently created with yttrium segregation at the surface at the higher annealing temperature are considered inactive to oxygen incorporation reactions. Our results provide additional insight into the interplay between the surface chemistry, microstructures, and electrochemical activity. They potentially provide important guidelines for engineering the electrolyte electrode interfaces of solid oxide fuel cells for higher electrochemical performance.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Durability of Polymer Electrolyte Membrane Fuel Cells Operated at Subfreezing Temperatures

The structure, composition, and interfaces of membrane electrode assemblies (MEA) and gas-diffusion layers (GDLs) have a significant effect on the performance of single-proton-exchange-membrane (PEM) fuel cells operated isothermally at subfreezing temperatures. During isothermal constant-current operation at subfreezing temperatures, water forming at the cathode initially hydrates the membrane, then forms ice in the catalyst layer and/or GDL. This ice formation results in a gradual decay in voltage. High-frequency resistance initially decreases due to an increase in membrane water content and then increases over time as the contact resistance increases. The water/ice holding capacity of a fuel cell decreases with decreasing subfreezing temperature (-10°C vs. -20°C vs. -30°C) and increasing current density (0.02 A cm -2 vs. 0.04 A cm -2 ). Ice formation monitored using in-situ high-resolution neutron radiography indicated that the ice was concentrated near the cathode catalyst layer at low operating temperatures (≈-20°C) and high current densities (0.04 A cm -2 ). Significant ice formation was also observed in the GDLs at higher subfreezing temperatures (≈-10°C) and lower current densities (0.02 A cm -2 ). These results are in good agreement with the long-term durability observations that show more severe degradation at lower temperatures (-20°C and -30°C).

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2024

Self‐Templated 3D Sulfide‐Based Solid Composite Electrolyte for Solid‐State Sodium Metal Batteries

Abstract Rechargeable solid‐state sodium metal batteries (SSMBs) experience growing attention owing to the increased energy density (vs Na‐ion batteries) and cost‐effective materials. Inorganic sulfide‐based Na‐ion conductors also possess significant potential as promising solid electrolytes (SEs) in SSMBs. Nevertheless, due to the highly reactive Na metal, poor interface compatibility is the biggest obstacle for inorganic sulfide solid electrolytes such as Na 3 SbS 4 to achieve high performance in SSMBs. To address such electrochemical instability at the interface, new design of sulfide SE nanostructures and interface engineering are highly essential. In this work, a facile and straightforward approach is reported to prepare 3D sulfide‐based solid composite electrolytes (SCEs), which utilize porous Na 3 SbS 4 (NSS) as a self‐templated framework and fill with a phase transition polymer. The 3D structured SCEs display obviously improved interface stability toward Na metal than pristine sulfide. The assembled SSMBs (with TiS 2 or FeS 2 as cathodes) deliver outstanding electrochemical cycling performance. Moreover, the cycling of high‐voltage oxide cathode Na 0.67 Ni 0.33 Mn 0.67 O 2 (NNMO) is also demonstrated in SSMBs using 3D sulfide‐based SCEs. This study presents a novel design on the self‐templated nanostructure of SCEs, paving the way for the advancement of high‐energy sodium metal batteries.

Guo, Xiaolin↗
DOE OSTI2015

Operational constraints and strategies for systems to effect the sustainable, solar-driven reduction of atmospheric CO 2

The operational constraints for a 6-electron/6-proton CO 2 reduction system that operates at the concentration of CO 2 in the current atmosphere (p CO 2 = 400 ppm) have been evaluated on a variety of scale lengths that span from laboratory scale to global scale. Due to the low concentration of CO 2 in the atmosphere, limitations due to mass transport of CO 2 from the tropopause have been evaluated through five different regions, each with different characteristic length scales: the troposphere; the atmospheric boundary layer (ABL); the canopy layer; a membrane layer; and an aqueous electrolyte layer. The resulting CO 2 conductances, and associated physical transport limitations, will set the ultimate limit on the efficiency and areal requirements of a sustainable solar-driven CO 2 reduction system regardless of the activity or selectivity of catalysts for reduction of CO 2 at the molecular level. At the electrolyte/electrode interface, the steady-state limiting current density and the concomitant voltage loss associated with the CO 2 concentration overpotential in a one-dimensional solar-driven CO 2 reduction cell have been assessed quantitatively using a mathematical model that accounts for diffusion, migration and convective transport, as well as for bulk electrochemical reactions in the electrolyte. At p CO 2 = 400 ppm, the low diffusion coefficient combined with the low solubility of CO 2 in aqueous solutions constrains the steady-state limiting current density to <0.1 mA cm -2 in a typical electrochemical cell with natural convection and employing electrolytes with a range of pH values. Hence, in such a system, the CO 2 capture area must be 100- to 1000-fold larger than the solar photon collection area to enable a >10% efficient solar-driven CO 2 reduction system (based on the solar collection area). This flux limitation is consistent with estimates of oceanic CO 2 uptake fluxes that have been developed in conjunction with carbon-cycle analyses for use in coupled atmosphere/ocean general circulation models. Two strategies to improve the feasibility of obtaining efficient and sustainable CO 2 transport to a cathode surface at p CO 2 = 400 ppm are described and modeled quantitatively. The first strategy employs yet unknown catalysts, analogous to carbonic anhydrases, that dramatically accelerate the chemically enhanced CO 2 transport in the aqueous electrolyte layer by enhancing the acid–base reactions in a bicarbonate buffer system. The rapid interconversion from bicarbonate to CO 2 in the presence of such catalysts near the cathode surface would in principle yield significant increases in the steady-state limiting current density and allow for >10% solar-fuel operation at the cell level. The second strategy employs a thin-layer cell architecture to improve the diffusive transport of CO 2 by use of an ultrathin polymeric membrane electrolyte. Rapid equilibration of CO 2 at the gas/electrolyte interface, and significantly enhanced diffusive fluxes of CO 2 in electrolytes, are required to increase the steady-state limiting current density of such a system. This latter approach however only is feasible for gaseous products, because liquid products would coat the electrode and therefore thicken the hydrodynamic boundary layer and accordingly reduce the diffusive CO 2 flux to the electrode surface. Regardless of whether the limitations due to mass transport to the electrode surface are overcome on the laboratory scale, at global scales the ultimate CO 2 flux limitations will be dictated by mass transport considerations related to transport of atmospheric CO 2 to the boundary plane of the solar-driven reactor system. The transport of CO 2 across the troposphere/ABL interface, the ABL/canopy layer interface, and the canopy layer/electrolyte interface have therefore been assessed in this work, to provide upper bounds on the ultimate limits for the solar-to-fuel (STF) conversion efficiency for systems that are intended to effect the reduction of atmospheric CO 2 in a sustainable fashion at global scale.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2026

Mechanistic insights into CO 2 capture and electrochemical conversion in nonaqueous Na–CO 2 batteries

Developing efficient energy storage systems that capture and convert CO 2 is critical for mitigating carbon emissions. Here, we report a Na–CO 2 battery with ruthenium dioxide (RuO 2 ) cathode catalysts and propane-1,3-diamine (PDA) as an electrolyte additive to enhance CO 2 capture and conversion efficiency. The integration of CO 2 adsorption and electrochemical reduction facilitates activation of the inert CO 2 molecule and circumvents gas–solid–liquid ternary-phase reactions at the interface. We employed density functional theory (DFT) calculations to systematically unravel the reaction mechanisms and energetics governing CO 2 reduction, both with and without PDA. Our results reveal an energetically favorable pathway toward the formation of Na 2 CO 3 and C as final discharge products, rather than sodium oxalate (Na 2 C 2 O 4 ). The CO 2 –amine adduct facilitates charge transfer from PDA to CO 2 , which results in activation of CO 2 . The kinetics of CO 2 conversion and regeneration of PDA were found to be significantly enhanced on the RuO 2 surface compared to the bulk electrolyte. More importantly, pre-activation of CO 2 via the amine–CO 2 adduct lowers the total overpotential to 2.44 V, compared to 3.13 V without PDA. This study provides fundamental insights into CO 2 electroreduction in Na–CO 2 batteries and underscores the promise of electrolyte engineering for sustainable CO 2 utilization and high-performance energy storage.

25 ENERGY STORAGE↗
DOE OSTI2021

Copper Dendrites and Surface Engineering for Enhanced CO2 Reduction Research Report Paper

The electrocatalytic reduction of CO 2 (CO 2 R) into hydrocarbon fuels, such as ethylene and ethanol, provides an attractive pathway towards closing the industrial carbon cycle and producing chemicals using renewable electricity. Existing CO 2 R technologies can exhibit C 2+ product selectivity above 74% and operating current densities over 1.3 A/cm 2 , but none can achieve both simultaneously, limiting the commercial viability and scalability of this technology. Low CO 2 concentrations at the catalyst surface and competing side reactions such as the hydrogen evolution reaction (HER) inhibit C 2+ faradaic efficiencies and operational current densities. Additionally, the use of high surface area cathode geometries to increase operational current densities is under-investigated. In this work, we electrodeposit a macroporous copper dendrite film to form high surface area cathodes. These structures are then coated with a combination of hydrophobic/hydrophilic ionomers to achieve high electrochemically active surface areas (ECSA), form regions of intrinsic porosity, and maximize catalytic availability of CO 2 . Using these techniques, we hope to maximize C 2+ faradaic efficiencies (FE) and geometric partial current densities. The treated cathode compound macrostructure (~10μm-sized pores, and ~μm-long dendrites) and concomitant surface area allows increased geometric current densities while the ionomer coating simultaneously inhibits HER and increases hydrogen availability to improve C 2+ selectivity. Our results show that careful engineering of the catalyst-electrolyte interface can enhance CO 2 reduction product selectivity and efficiency.

10 SYNTHETIC FUELS↗
NASA NTRS1997

Polymer membrane based electrolytic cell and process for the direct generation of hydrogen peroxide in liquid streams

An electrolytic cell for generating hydrogen peroxide is provided including a cathode containing a catalyst for the reduction of oxygen, and an anode containing a catalyst for the oxidation of water. A polymer membrane, semipermeable to either protons or hydroxide ions is also included and has a first face interfacing to the cathode and a second face interfacing to the anode so that when a stream of water containing dissolved oxygen or oxygen bubbles is passed over the cathode and a stream of water is passed over the anode, and an electric current is passed between the anode and the cathode, hydrogen peroxide is generated at the cathode and oxygen is generated at the anode.

White, James H.↗
DOE OSTI2024

Phloroglucinol–2,6‐Diaminoanthraquinone as a Durable Redox Mediator for Enhancing Conversion Reaction Kinetics in Lithium‐Sulfur Batteries

Abstract Lithium‐sulfur batteries, despite being a promising solution for next‐generation secondary batteries, require substantial efforts to overcome the challenges of sluggish sulfur redox kinetics, polysulfides shuttling, and Li metal instability before achieving practical viability. Conventional strategies that utilize metal catalysts or soluble redox mediators (RMs) are limited by either impractical producing processes or unsatisfactory service life. Herein, an electrochemically active organic material, phloroglucinol – 2,6‐diaminoanthraquinone (PG‐DAAQ) is synthesized through a green and facile polymerization process to better resolve these issues. Serving as an RM at the cathode, PG‐DAAQ exhibits enduring redox activity within the sulfur operating potential window, leading to enhanced redox kinetics and sulfur utilization. Remarkably, even without any metal elements, PG‐DAAQ exhibits an excellent affinity to polysulfides, thereby suppressing the shuttling and facilitating the formation of a more favorable solid‐electrolyte interface to stabilize Li deposition at the anode. As a result, Li‐S cells employing PG‐DAAQ show significantly enhanced cycling and rate performances than the control cells. Even with a low electrolyte‐to‐sulfur ratio of 6, pouch cells with PG‐DAAQ deliver a reversible discharge capacity of 821 mA h g −1 after 100 cycles at a C/10 rate.

Lai, Tianxing↗
DOE OSTI2023

Multidimensional visualization of the dynamic evolution of Li metal via in situ/operando methods

The growing demands for high-energy density electrical energy storage devices stimulate the coupling of conversion-type cathodes and lithium (Li) metal anodes. While promising, the use of these “Li-free” cathodes brings new challenges to the Li anode interface, as Li needs to be dissolved first during cell operation. In this study, we have achieved a direct visualization and comprehensive analysis of the dynamic evolution of the Li interface. The critical metrics of the interfacial resistance, Li growth, and solid electrolyte interface (SEI) distribution during the initial dissolution/deposition processes were systematically investigated by employing multidimensional analysis methods. They include three-electrode impedance tests, in situ atomic force microscopy, scanning electrochemical microscopy, and cryogenic scanning transmission electron microscopy. The high-resolution imaging and real-time observations show that a loose, diffuse, and unevenly distributed SEI is formed during the initial dissolution process. This leads to the dramatically fast growth of Li during the subsequent deposition, deviating from Fick’s law, which exacerbates the interfacial impedance. The compactness of the interfacial structure and enrichment of electrolyte species at the surface during the initial deposition play critical roles in the long-term stability of Li anodes, as revealed by operando confocal Raman spectroscopic mapping. In conclusion, our observations relate to ion transfer, morphological and structural evolution, and Li (de)solvation at Li interfaces, revealing the underlying pathways influenced by the initial dissolution process, which promotes a reconsideration of anode investigations and effective protection strategies.

25 ENERGY STORAGE↗
DOE OSTI2018

Numerical Simulation of Multiphase Magnetohydrodynamic Flow and Deformation of Electrolyte–Metal Interface in Aluminum Electrolysis Cells

A computational fluid dynamics based multiphase magnetohydrodynamic (MHD) flow model for simulating the melt flow and bath–metal interface deformation in realistic aluminum reduction cells is presented. The model accounts for the complex physics of the MHD problem in aluminum reduction cells by coupling two immiscible fluids, electromagnetic field, Lorentz force, flow turbulence, and complex cell geometry with large length scale. Especially, the deformation of bath–metal interface is tracked directly in the simulation, and the condition of constant anode–cathode distance (ACD) is maintained by moving anode bottom dynamically with the deforming bath–metal interface. The metal pad deformation and melt flow predicted by the current model are compared to the predictions using a simplified model where the bath–metal interface is assumed flat. The effects of the induced electric current due to fluid flow and the magnetic field due to the interior cell current on the metal pad deformation and melt flow are investigated. The presented model extends the conventional simplified box model by including detailed cell geometry such as the ledge profile and all channels (side, central, and cross-channels). The simulations show the model sensitivity to different side ledge profiles and the cross-channel width by comparing the predicted melt flow and metal pad heaving. In addition, the model dependencies upon the reduction cell operation conditions such as ACD, current distribution on cathode surface and open/closed channel top, are discussed.

42 ENGINEERING↗
DOE OSTI2023

Stabilizing magnesium plating by a low-cost inorganic surface membrane for high-voltage and high-power Mg batteries

Mg batteries with halide-free electrolytes suffer from poor stability of the Mg metal anode due to electrolyte decomposition. Here, we report a low-cost zeolite membrane supported on Mg to address this challenge. It vastly reduces the population (hence decomposition) of free diglyme at the Mg/electrolyte interface, while allowing facile transport of Mg 2+ cations through the membrane. We demonstrate dendrite-free Mg plating/stripping performance in a magnesium tetrakis(hexafluoroisopropyloxy)borate/diglyme electrolyte with a 750-fold extended lifetime (over 6,000 h) and a high coulombic efficiency of ~98%. The prototype Mo 3 S 4 cathode paired with the protected Mg anode shows 91% capacity retention over 200 cycles. Importantly, this membrane protects soluble species in a high-voltage organic polymer cathode from being reduced at the anode via shuttling, achieving a full cell with a 3.5 V cutoff voltage. This results in a high specific energy density of 320 Wh kg –1 and a power density of 1,320 W kg –1 based on cathode mass.

25 ENERGY STORAGE↗
DOE OSTI2026

Rational Design of Weakly‐Solvating Molecules for Salt‐In‐Pre‐Ionic‐Liquid Electrolytes for Li Metal Batteries

Lithium metal batteries (LMBs) promise step‐changes in energy densities but suffer from poor cycle life due to unstable electrolyte‐lithium interfaces. Conventional carbonate electrolytes exhibit excessive lithium‐ion solvation and low oxidative stability, leading to rapid capacity loss. Herein, we report a rationally designed weakly‐solvating cyclic sulfonamide, 1‐trifluoromethanesulfonyl)amide pyrrolidine (TFMSPyr), which integrates an electron‐withdrawing trifluoromethanesulfonyl functional group at pyrrolidinic‐N. TFMSPyr acts as a pre‐ionic‐liquid solvent that forms intrinsically localized, anion‐dominated solvation, coupling molecular architecture, solvation topology, and transport dynamics. As a result, LiFSI based salt‐in‐pre‐ionic‐liquid (SIPIL) electrolytes exhibit high lithium‐ion transference number, oxidative stability > 5 V versus Li/Li + and anion‐derived solid electrolyte interphases (SEI). Li||Cu cells with SIPIL deliver a first cycle Coulombic efficiency (CE) of ≈ 99% with average CE of 99.2% for 100 cycles, and lithium half‐cells with lithium iron phosphate (LFP) cathode exhibit 82% capacity retention after 400 cycles with CE of 99.98%. In anode‐free full cells, 95% of initial capacity is retained after 63 cycles with an average CE of 99.5%. These results demonstrate that molecular engineering of solvents offers a powerful pathway to stabilize lithium metal interfaces and enable practical Anodeless LMBs.

25 ENERGY STORAGE↗
DOE OSTI2021

Exposure History and its Effect Towards Stabilizing Li Exchange Across Disordered Rock Salt Interfaces

Abstract The application of lithium rich disordered rock salts (DRX) as cathode materials has greatly expanded the materials space for high energy density cathodes. These materials are able to consistently achieve capacities higher than via a complex percolation based intercalation mechanism. Most current DRX materials face significant capacity fade when cycled over an extended period. One of the factors responsible for this could be deleterious side effect of interface reactions between the electrode and electrolyte at high voltage. We aim to focus on one aspect of this interaction, i.e the effect of exposure to electrolyte on the surface and its effect on the electrochemical properties of (LMNOF) powder. LMNOF was systematically treated in an electrolyte solution for varying periods of time at an elevated temperature. Treated samples exhibit surface layer modification (removal of F rich surface layer), leading to a 10 % improvement in the capacity retention behavior of LMNOF. Surface and bulk based measurements indicate an increase in disorder and gradual removal of F and Li. All of these processes mimic an aging process similar to cycling. This a priori formed interface allows for increased stability with respect to retention of capacity and oxygen loss.

Satish, Rohit↗
DOE OSTI2025

Thermal decomposition pathways of bulk electrolytes on vanadium oxide nanocrystals

The thermal stability of electrolytes at an elevated temperature induced by battery charge-discharge cycling is critical for the long cycling performance of a rechargeable battery. For many multivalent systems, such as rechargeable magnesium batteries, which offer great potential for high energy density and utilize earth-abundant resources, electrolyte instability and electrode surface passivation, arising from electrolyte decomposition, remain as major roadblocks. Understanding the electrolyte decomposition pathways at the electrode-electrolyte interface is essential to provide guidance in overcoming this challenge. In this work, in situ 13 C magic angle spinning nuclear magnetic resonance (MAS NMR) and first-principles calculations were used to investigate the thermal decomposition of the electrolyte in a system consisting of MgV 2 O 4 , a novel cathode for magnesium batteries, mixed with a bulk electrolyte consisting of magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI) 2 ) in diglyme (G2). We show that significant electrolyte decomposition is observed in bulk 1.0 M Mg(TFSI) 2 in G2 mixed with nanometer sized MgV 2 O 4 powder at elevated temperatures. This observation is to mimic the possible thermal decomposition that might happen during battery cycling. We demonstrate that the MgV 2 O 4 surface is covered by a layer of decomposed G2 products. We conclude that the dominant reaction pathway for electrolyte decomposition is the thermal decomposition of the pure electrolytes at elevated temperatures, followed by adsorption of G2 decomposition products to the MgV 2 O 4 surface. The activation energy for the major decomposition pathway is obtained. In conclusion, this work highlights the importance of studying thermal decomposition of electrolytes for overall system stability and explores electrolyte stability at significantly elevated temperatures.

25 ENERGY STORAGE↗
DOE OSTI2023

Ultrasmooth Epitaxial Pt Thin Films Grown by Pulsed Laser Deposition

Platinum (Pt) thin films are useful in applications requiring high-conductivity electrodes with excellent thermal and chemical stability. Ultrasmooth and epitaxial Pt thin films with single-crystalline domains have the added benefit of providing ideal templates for the subsequent growth of heteroepitaxial structures. Here, we grow epitaxial Pt (111) electrodes (ca. 30 nm thick) on sapphire (α-Al 2 O 3 (0001)) substrates with pulsed laser deposition. This versatile technique allows control of the growth process and fabrication of films with carefully tailored parameters. X-ray scattering, atomic-force microscopy, and electron microscopy provide structural characterization of the films. Various gaseous atmospheres and temperatures were explored to achieve epitaxial growth of films with low roughness. A two-step (500 °C/300 °C) growth process was developed, yielding films with improved epitaxy without compromising roughness. The resulting films possess ultrasmooth interfaces (<3 Å) and high electrical conductivity (6.9 × 10 6 S/m). Finally, Pt films were used as current collectors and templates to grow lithium manganese oxide (LiMn 2 O 4 (111)) epitaxial thin films, a cathode material used in Li-ion batteries. In conclusion, using a solid-state ionogel electrolyte, the films were highly stable when electrochemically cycled in the 3.5-4.3 V vs Li/Li + range.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Advances in electrode materials for Li-based rechargeable batteries

Rechargeable lithium-ion batteries store energy as chemical energy in electrode materials during charge and can convert the chemical energy into electrical energy when needed. Tremendous attention has been paid to screen electroactive materials, to evaluate their structural integrity and cycling reversibility, and to improve the performance of electrode materials. This review discusses recent advances in performance enhancement of both anode and cathode through nanoengineering active materials and applying surface coatings, in order to effectively deal with the challenges such as large volume variation, instable interface, limited cyclability and rate capability. We also introduce and discuss briefly the diversity and new tendencies in finding alternative lithium storage materials, safe operation enabled in aqueous electrolytes, and configuring novel symmetric electrodes and lithium-based flow batteries.

25 ENERGY STORAGE↗
DOE OSTI2022

PGM-Free Oxygen-Reduction Catalyst Development for Proton-Exchange Membrane Fuel Cells: Challenges, Solutions, and Promises

Proton-exchange membrane fuel cells (PEMFCs) are efficient and clean hydrogen energy technologies for transportation and stationary applications. Highly active and durable low-cost cathode catalysts for the oxygen-reduction reaction (ORR) under challenging acidic environments are desperately needed to address the cost and durability issues of PEMFCs. The most promising platinum group metal (PGM)-free catalysts for the ORR in acidic media are atomically dispersed and nitrogen-coordinated metal site catalysts denoted as M–N–C, M = Fe, Co, or Mn. Due to significant efforts in the past few decades, these catalysts have demonstrated much-improved ORR activity and promising initial fuel cell performance approaching traditional Pt/C catalysts. However, the insufficient long-term stability (up to 5000 h) under PEMFC operation represents a primary technical barrier to making current PGM-free catalysts less viable yet in PEMFCs. In this Account, we highlight recent advances in synthesizing efficient PGM-free catalysts for the ORR in PEMFCs, emphasizing effective strategies to improve mass and intrinsic activity and the possible degradation mechanisms. In particular, a chemical doping method based on the zeolitic imidazolate framework (ZIF)-8 represents the key to developing efficient M–N–C catalysts containing atomically dispersed and nitrogen-coordinated single metal active sites (i.e., MN 4 ). The newly acquired understanding of the formation mechanism of MN 4 active sites during the thermal activation and its correlation to catalytic properties guide the rational catalyst design rather than relying on current trial-and-error approaches. Considerable efforts have further been invested in increasing the active site density and enhancing intrinsic activity by regulating carbon-phase structures and the local coordination environment. Furthermore, these highly active catalysts usually suffer from significant activity loss during the ORR. Therefore, breaking the activity–stability trade-off is the key to simultaneously achieving activity and stability in one catalyst, which is discussed on the basis of our recent successes in regulating local carbon structures surrounding active single metal sites. Significant research efforts toward understanding the degradation mechanisms and improving the lifetime of PGM-free catalysts are still crucial for viable applications in the future. Novel electrode designing strategies are needed to translate the PGM-free catalysts’ ORR activity to solid-state electrolyte-based membrane electrode assemblies (MEAs) with robust three-phase (i.e., gas–liquid–solid) interfaces for efficient charge and mass transports for performance improvement. On the basis of our effort at the University at Buffalo supported by ElectroCat Consortium associated with U.S. DOE’s Hydrogen and Fuel Cell Technologies Office, we provide a perspective on PGM-free cathode catalysts concerning remaining bottlenecks and future opportunities, aiming to inspire the community in both mechanistic understanding and technological development.

08 HYDROGEN↗
DOE OSTI2021

F and N Rich Solid Electrolyte for Stable All-Solid-State Battery

We report the instability of sulfide solid electrolytes to Li anode and high-voltage LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) cathodes limits the cyclic performance of all-solid-state lithium battery (ASSLB). Herein, the stability of Li 6 PS 5 Cl against Li anode is enhanced by mixing a small amount (0.32 wt%) of CuF 2 -LiNO 3 (CL) into Li 6 PS 5 Cl electrolyte layer to in-situ form a mixed-conductive-lithiophobic and self-healing LiF-Li 3 N-Cu solid electrolyte interphase (SEI) at Li 6 PS 5 Cl-CL/Li interface. The critical current density (CCD) of Li 6 PS 5 Cl-CuF 2 -LiNO 3 increases to 1.4 mA cm –2 /1.4 mAh cm –2 at room temperature, which is much higher than that of pristine Li 6 PS 5 Cl (0.4 mA cm –2 /0.4 mAh cm –2 ) even though mixing 0.32 wt% CL into Li 6 PS 5 Cl slightly reduces the ionic conductivity from 2.9 × 10 –3 to 1.5 × 10 –3 S cm –1 . The compatibility of Li 6 PS 5 Cl-CL electrolyte to single-crystalline NMC811 (S-NMC811) is further enhanced by adding a small amount (0.02 wt%) of AlF 3 into Li 6 PS 5 Cl-CL forming Li 6 PS 5 Cl-CuF 2- LiNO 3 -AlF 3 (Li 6 >PS 5 Cl-CLA) as a cathode electrolyte and by doing Cl – on S-NMC811 (Cl@S-NMC811) surface. The Cl@S-NMC811-Li 6 PS 5 Cl-CLA|Li 6 PS 5 Cl-CL|Li cells with areal capacity of 2.55 mAh cm -2 achieve a capacity retention of 69.4% after 100 cycles at 1C (1C = 200 mAh g -1 ). Adding a small amount of SEI and cathode/electrolyte interphase (CEI) former into the sulfide electrolytes with minimal reduction (48.3%) of ionic conductivity is an effective method to enhance the performance of ASSLB.

36 MATERIALS SCIENCE↗