Cu-based Anodes Research Articles

Seeding and Growing Plain Li-Metal Surfaces - New Approaches to Increase the Coulombic Efficiency of Anodeless Lithium-Metal Batteries

In the pursuit of higher energy densities, lithium-ion batteries with lithium metal anode appear as one particular promising technology. Especially the option to plate non-dendritic, superficially even Li-layers [1] directly onto the current collector of the negative electrode without the use of an anode active material (“anode-less battery design”) should enable gravimetric energy densities of up to 400 Wh/kg [2] and 1200 Wh/l [3] in future cell systems [4].In the presented work, Swagelok-cells in “anode-less” configuration, comprising a NMC 811-cathode and an ether-based electrolyte containing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and 1,2-dimethoxyethane (DME) in 1.2:3 molar ratio, 1.5 M LiFSI [2] were cycled under the application of pressure (up to 400 kPa) onto the cell stack.As the proper formation of Li-nuclei (number, morphology, etc.) and the even growth of lithium-layers onto the Cu-based anode (Figure 1) seems from great importance to plate and stripe Li-metal at high coulombic efficiencies, several charging programs with presumably Li-nucleation promoting effects were tested in a cycling experiment along 50 full cycles (Figure 2). As a promising result and as clear improvement compared to standard charging processes (e.g. 0.1 C), average coulombic efficiencies as high as 99.2 % together with low capacity fading were observed.Due to the design-related limitation of Swagelok-based cells and a noticeable diffusion of air fractions (N2, O2, H2O) across the PFA-seals into the cell, in a second experimental part the influence of ambient air on the cycling performance was tested under three conditions (Figure 2, left, middle and right diagram): a) Cells cycling in common (humid), laboratory air, b) under dry air (P2O5) in sealed steel-containers and c) inside an argon filled glovebox (< 0.1 ppm H2O, < 0.1 ppm O2). As a result, a strong sensitivity of operating Li-metal cells not solely versus traces of ambient, humid air, but also versus P2O5-dried nitrogen and oxygen was obvious. Reference s [1] Fang, C.; Lu, B.; Pawar, G.; Zhang, M.; Cheng, D.; Chen, S.; Ceja, M.; Doux, J.-M.; Musrock, H.; Cai, M.; Liaw, B.; Meng, Y. S., Pressure-tailored lithium deposition and dissolution in lithium metal batteries. Nature Energy 2021, 6, (10), 987-994.[2] Niu, C.; Liu, D.; Lochala, J. A.; Anderson, C. S.; Cao, X.; Gross, M. E.; Xu, W.; Zhang, J.-G.; Whittingham, M. S.; Xiao, J.; Liu, J., Balancing interfacial reactions to achieve long cycle life in high-energy lithium metal batteries. Nature Energy 2021, 6, (7), 723-732.[3] Louli, A. J.; Eldesoky, A.; Weber, R.; Genovese, M.; Coon, M.; deGooyer, J.; Deng, Z.; White, R. T.; Lee, J.; Rodgers, T.; Petibon, R.; Hy, S.; Cheng, S. J. H.; Dahn, J. R., Diagnosing and correcting anode-free cell failure via electrolyte and morphological analysis. Nature Energy 2020, 5, (9), 693-702.[4] Li, Q.; Yang, Y.; Yu, X.; Li, H., A 700 W⋅h⋅kg−1 Rechargeable Pouch Type Lithium Battery. Chinese Physics Letters 2023, 40, (4), 048201. Figure 1

Rotating Disk Electrode Studies of Benzaldehyde Oxidation on Group Ib Metals

Water electrolysis is a green means of producing hydrogen gas to be used as a fuel or reactant in key industrial processes such as ammonia production. The conventional system of oxygen evolution (OER) and hydrogen evolution (HER) suffers from slow kinetics at the anode and a high cell voltage limited by thermodynamics. One solution is to replace OER with another reaction such as an organic oxidation reaction that has a lower equilibrium potential and produces a valuable organic byproduct at the anode. Recent work has demonstrated that biomass-derived aldehydes such as furfural and 5-hydroxymethylfurfural can be selectively oxidized to their corresponding carboxylates and H2 on Cu-based anodes at low potentials (~0.1 VRHE) in alkaline media. In alkaline media, a hydroxide ion adds to the carbonyl carbon of an aldehyde molecule forming a gem diolate in solution phase. It is argued that dehydrogenation becomes more facile due to the weaker C-H bond of the gem diolate compared to the aldehyde form of the molecule. This may enable oxidation without the need for coadsorbed-OH. Additionally, aldehyde oxidation is only active on Au, Ag, and Cu electrodes at higher pHs.The aim of this work is to identify the conditions under which low potential oxidation of aldehydes and high anodic Faradaic efficiency to H2 occurs, namely, electrode material and applied potential. To avoid polymerization side reactions of furans in alkaline media, we studied benzaldehyde as a model compound which has also been shown to exhibit low potential oxidation and anodic H2. The activity (rate of aldehyde consumption) and selectivity (to anodic H2 versus H2O) were compared for the group Ib metals (Au, Ag, Cu), each of which demonstrates a relatively early onset potential (<0.4 VRHE) and generates anodic H2 at certain potentials. Rotating disk electrode studies with Koutecky-Levich analysis were conducted to separate mass transfer effects from kinetic current to compare the intrinsic activity of each electrode. Additionally, the average number electrons transferred per aldehyde molecule consumed was estimated from Koutecky-Levich analysis; the one-electron pathway combines the aldehyde hydrogens to H2 while the two-electron pathway requires an additional electron per aldehyde molecule to oxidize the hydrogen from the surface to form H2O. Rotating ring disk electrode studies were used to further validate the anodic H2 generation as a Pt ring was still able to oxidize H2 despite the presence of benzaldehyde. This was used as an additional means of estimating the selectivity to H2 as a function of potential.CVs for benzaldehyde oxidation on each metal are shown in Figure a. Peak current followed the order of Au > Ag >> Cu. Au reached a mass transfer limiting current, and Ag also showed an RPM dependence but did not reach full mass transfer limitations. Cu was the least active and did not show any mass transfer dependence. On the other hand, Cu has the earliest onset potential followed by Ag then Au. The average number of electrons transferred per aldehyde molecule according to RRDE measurements is shown in Figure b, where one electron represents H2 and two electrons represents H-oxidation to H2O. Cu had 100% selectivity to H2 over its entire potential window of activity (up to 0.45 VRHE). Au and Ag have high selectivity to H2 at low potentials but decreases to near zero H2 production in the range of 0.6-0.8 VRHE; the decrease in selectivity to H2 on Ag occurs slightly earlier than Au (~0.1 V). H2 selectivity is related to the inability of each metal to oxidize H to H2O at low potentials. Figure 1

Bias-free photoelectrochemical system mediates hydrogen production and biomass conversion at high current density

The construction of a bias-free photoelectrochemical (PEC) system is a promising approach to producing renewable fuels and chemicals from solar energy. However, the conventional anodic reaction of oxygen evolution reaction (OER) possesses slow kinetics and a large overpotential. In this study, 5-Hydroxymethylfurfural (HMF) oxidation on a Cu-based anode is introduced to be paired with a cathodic HER on p-Si/CdS/Pt photocathode. Due to the semi-oxidized structure of Cu+, the anode Cu2O-CF achieves an onset potential of 0.05 V vs RHE and ∼100% FEHMFCA under ∼80 mA/cm2, which reduces the anodic potential by ∼1.6 V compared with OER. The p-Si based heterojunction photocathode exhibits an onset potential of 0.45 V vs RHE and a photocurrent of ∼30 mA/cm2 (0 V vs RHE), providing a large photovoltage of 450 mV. As a result, the tandem configuration can achieve bias-free anodic FEHMFCA of 84% and cathodic FEH2 of 95% at 15 mA/cm2 after optimizing the compatibility of the cathode and anode. This strategy provides a new possibility for the construction of an unbiased photo-assisted solar-to-chemical system.

Highly Active and Stable Cu-Based Anode Decorated with In Situ Fabricated CuFe Alloy Nanoparticles for Solid Oxide Fuel Cells

Uniformly distributed CuFe bimetallic alloy (CFA) nanoparticle-decorated Ruddlesden–Popper (RP) structure PrSr(Cu,Fe)0.9Mn0.1O4-δ perovskite (RP-PSCFM-CFA) had been synthesized by in situ annealing cubic perovskite Pr0.5Sr0.5Cu0.1Fe0.8Mn0.1O3-δ in a wet H2 atmosphere at 800 °C. The precipitated nanoparticles effectively improved the electrochemical properties of the RP-PSCFM-CFA when it was used as the solid oxide fuel cell anode. The La0.8Sr0.2Ga0.83Mg0.17O3−δ electrolyte-supported single cell can reach maximum power densities of 0.996 and 0.410 W cm–2 in H2 and C3H8 at 800 °C, respectively. Moreover, the single cell showed a superior stable performance in C3H8 at 800 °C with a constant current density of 0.8 A cm–2, indicating that the RP-PSCFM-CFA anode has an excellent catalytic capacity and certain anticarbon performance. This study offers the possibility of further extensive development of Cu-based perovskite anodes.

Co-fired anode-supported solid oxide fuel cell for internal reforming of hydrocarbon fuel

Hydrocarbon-based solid oxide fuel cell (SOFC) is being projected as one of the possible alternatives to conventional internal combustion engines. However, the conventional Ni–YSZ anode is prone to carburization in the presence of hydrocarbon fuels. In the present study, an optimized Ni–Cu-based anode composition (Ni0.9–Cu0.1–YSZ0.95–GDC0.05) has been evolved based on accelerated carburization studies and phase analysis by X-ray diffractometry and X-ray photoelectron spectroscopy. The electrochemical parameters have been derived for the optimized anode composition, and its exchange current density is estimated to be 76.3 mA cm−2 at 780 °C. The main advantage of the optimized anode is its suitability for co-firing with the electrolyte. Using the optimized anode composition, anode-supported SOFC single cells (ASCs) have been fabricated and their electrical and electrochemical performances have been evaluated and compared with conventional ASC. The anode-supported co-cast SOFC with the optimized anode composition exhibits a power density of 436 mW cm−2 at 850 °C and 0.5 V with methane as fuel.

Structural features of the magnetron sputtered CuO/GDC anodes for solid oxide fuel cells

The paper presents the results of the research of structure of a thin film CuO/Ce0.9Gd0.1O2-δ (CuO/GDC) anode for solid oxide fuel cells (SOFCs) prepared by magnetron sputtering. Cu-based anode materials of SOFCs are of great interest because they exhibit greater tolerance to sulfur-containing fuels than the widely used Ni-based composite anodes. After deposition, annealing in air and reducing atmospheres, the composition, microstructure and crystallinity of the films were characterized using energy dispersive X-Ray spectroscopy, scanning electron microscopy and X-ray diffractometry, respectively. The as-deposited film consists of cubic fluorite structures of GDC and Cu2O and has a dense, homogeneous structure, in which Cu is evenly distributed over the volume of the film. However, it was shown that, strong Cu segregation is observed in CuO/GDC films, after reduction in hydrogen at a temperature of 750 °C, with the formation of massive agglomerates on the surface. The influence of pre-calcination of the as-deposited films at 1000 °C and 1200 °C on their structure was studied. It is shown that annealing at a temperature of 1000 °C does not prevent the agglomeration of Cu in a reducing atmosphere, while Cu evaporation is observed if annealing temperature is 1200 °C.

Ex situ identification of the Cu+ long-range diffusion path of a Cu-based anode for lithium ion batteries.

An ex situ observation was made by XRD patterns, SEM and TEM images, as well as cyclic voltammogram curves of CuO/Cu integrated anodes for lithium ion batteries. For the first time, the existence of a Cu(+) ion long-range transfer path was identified at the potential widow of 1.30-1.60 V during both charging and discharging processes. Both SEM and TEM images show that these nanowires networks hanging CuO nanoparticles provide a Cu(+) diffusion path within our designed CuO/Cu integrated anode. This work provides new insights into the conversion reaction of inorganic anode materials, and can favor the development of high-performance conversion anodes for lithium-ion batteries.

Cathode Supports of SOFCs with a Hierarchical Pore Structure

Cathode-supported SOFCs are attractive for the potential utilization of hydrocarbons as fuels to generate electricity because Cu-based anodes can be used to deal with coke formation in the Ni-base anodes. However, Cu-based anodes cannot be used in anode-supported SOFCs because the high sintering temperatures (above 1350 °C) required for the formation of a dense electrolyte film may melt the Cu-based anodes. Compared with anode materials, cathode materials show higher sinterability, which leads to a low porosity of the supporting cathodes and in turn high gas diffusion resistance within the cathodes. To get around this problem, a novel supporting cathode with efficient gas diffusion channels will be developed in this study in order to achieve high performances in power generation.

The investigation of active Ni/YSZ interlayer for Cu-based direct-methane solid oxide fuel cells

In this study, dense YSZ (d_YSZ)–Ni/YSZ–porous YSZ (p_YSZ) double-layer anode structures were prepared by the tape casting–lamination–co-sintering (TLC) method to improve the stability of the cells due to the cracking reaction of methane. Cu was infiltrated into all cells as an electronic conductive material. The effect of CeO2 and SDC (samarium-doped ceria) loadings were also investigated. Stable operation was obtained by using a Ni-interlayered Cu-based anode structure for dry methane fuel at 800°C for 72h. No carbonization was observed after the addition of Cu to the cell. An interesting finding was that a highly loaded secondary material (CeO2 and SDC) leads to a regional break of the electronic conduction network, which decreases the number of active TPB regions. Therefore, carbonization occurred inside the cell in the Ni-containing interlayer zone. At the end of 72h of cell operation, carbonization was observed inside the Ni-containing and Ni-free regions in the SDC-containing cell. In addition to conducting cell tests, the behavior of powder SDC was studied under a dry methane environment by temperature-programmed surface reaction (TPR) and temperature-programmed oxidation (TPO) analysis.

Study on Diffusion of Copper of SOFC Cu-Based Anodes in Co-Sintering with Electrolyte

Cu-based anode has no or little catalytic activity to reaction of precipitating carbon during using carbon-hydrogen fuel, which can avoid failure or disintegration of SOFC caused by catalytically precipitating carbon resulting from Ni-based anode. However, the melting point of CuO, that is 1148°C, is far below the sintering temperature of electrolyte which limits the use of Cu-based anode. So the property of sintering of Cu-based anode between 1050°C and 1150°C was studied by co-pressing and co-sintering Cu-based anode with electrolyte. The result shows that the diffusion of copper in the electrolyte is not apparent when the co-sintering temperature is below 1130°C. At 1140°C, the Matano plane moved to anode side and the diffusion coefficient of copper in the electrolyte is relevant to concentration of copper which is 0.543×10-8-1.74×10-8(cm2•s-1) when the content of copper is 1.51%~18.7%.

On the Choice of Anode Electrocatalyst for Alcohol Fuelled Proton Conducting Solid Oxide Fuel Cells

Proton conducting solid oxide fuel cells (H+-SOFC) offer reduced temperature operation when compared to traditional oxygen anion conducting SOFCs. However, one potential drawback is a loss of fuel flexibility as H+-SOFCs require hydrogen as a fuel. In this study we examine the use of Ni, Ni-Cu, and Cu-based anodes for the internal steam reforming of methanol and ethanol on the H+-SOFC anode. When compared to hydrogen fuel, the cell performance is lower in all of the alcohol fuels due to lower hydrogen content in the reformate. Ni provides substantially higher performance than Cu due to increased steam reforming activity towards hydrogen production and may increase hydrogen incorporation kinetics. Significant carbon deposition was noted on the Ni anode when operating on ethanol fuel, even with a 4:1 steam:carbon ratio. Only limited carbon deposition was noted for the Cu anode. Alloying Ni with Cu was shown to help limit carbon formation at the anode.

Effect of adding urea on performance of Cu/CeO2/yttria-stabilized zirconia anodes for solid oxide fuel cells prepared by impregnation method

Anode microstructure has a great influence on the cell performance. The addition of urea into impregnated solution has been proposed to tailor the distribution and/or morphology of Cu when fabricating the Cu-based anodes by impregnation method. While the previous reports demonstrated the single cell performance has not been improved in this route, in this paper, fuel cells with Cu/yttria-stabilized zirconia (YSZ) and Cu–CeO2/YSZ anodes were fabricated and evaluated with improved outputs. The microstructure of Cu in anodes appeared significantly different after the addition of urea. The electronic conductivity obtained from the anodes impregnated with adding urea was twice as high as the ones without. Performance of fuel cells increases by 12% while operating on H2 at 700°C upon adding urea. Furthermore, the performance improvement was more prominent when such method was adopted in the fabrication of Cu–CeO2/YSZ composite anodes. Cells with Cu–CeO2/YSZ composite anodes operating in H2 at 700°C exhibited an increase of cell performance by 37%, from 337 to 462mWcm−2, by simply adding urea to the impregnated solution. And the performance enhancement for such fuel cells is also as high as 28% when using CH4 as fuel.

Preparation and characterization of copper based cermet anodes for use in solid oxide fuel cells at intermediate temperatures

Two Cu-based anode cermets suitable for direct hydrocarbon oxidation in Solid Oxide Fuel Cells (SOFC) based on yttria stabilized zirconia (YSZ) electrolyte were tested in the temperature range (500–800°C). The ceramic components were CeO2 and the perovskite La0.75Sr0.25Cr0.5Mn0.5O3−d (LSCM). The cermets were made in both the form of pellets and films applied onto the YSZ electrolytes. Pellets exhibited good mechanical strength and resistance to fracture in both oxidized and reduced state. Cu–LSCM cermets exhibited good redox cycling behavior between 700–800°C. Reduction temperature plays a significant role on final morphology with Cu segregation occurring at 800°C. Cu–LSCM films were found to exhibit lower polarization resistances than Cu–CeO2 under 5% H2. Examination of the data revealed a poorer contact of the Cu–CeO2 electrode with the YSZ surface than the Cu–LSCM electrode. Reduction temperature should be less than 750°C to ensure suitable microstructure and adhesion of both film electrodes with the electrolyte.

Enhanced Thermal Stability of Cu-Based SOFC Anodes by Electrodeposition of Cr

The electrodeposition of Cr onto Cu-based, solid oxide fuel cell (SOFC) electrodes was investigated. Cu–ceria–YSZ (yttria-stabilized zirconia) electrodes were prepared by impregnation of porous YSZ with aqueous solutions of and and modified by the addition of a Cr layer onto the Cu. The addition of Cr had no effect on anode performance at in humidified but significantly improved the thermal stability. Without Cr, scanning electron microscopy showed structural changes in the Cu films after heating to , resulting in increased ohmic resistances in impedance spectra. The addition of Cr increased thermal stability so that the anodes were unaffected by heating to in dry . Some oxidation of Cr was observed by X-ray diffraction following exposure of the composite to 80% mixtures at for , but partial oxidation of Cr did not affect the thermal stability of the anode. Exposure of the composite to 80% mixtures at for resulted in complete oxidation of the Cr and a loss of enhanced thermal stability. Attempts to prevent Cr oxidation by the electrodeposition of Cu onto the Cr were unsuccessful. Based on these results, strategies for enhancing the stability of Cu-based anodes are discussed.

Methanol as a direct fuel in intermediate temperature (500– [formula omitted]) solid oxide fuel cells with copper based anodes

Various Cu-based anodes have been evaluated for use in intermediate temperature (500– 600 ∘ C ) solid oxide fuel cells operating on methanol fuel. A range of Cu–CGO cermets prepared by conventional powder/slurry routes were investigated by varying the composition, source materials and sintering temperature. These anodes were adherent to the electrolyte when reduced in H 2 but were found to be unstable during operation in dry methanol, leading to delamination of the anode from the electrolyte. CeO 2 impregnated Cu electrodes were found to be resistant to delamination, act as methanol decomposition catalysts and displayed reasonable performance when running on dry methanol, with no sign of coke formation. However, these anodes undergo sintering when operating at 600 ∘ C , leading to loss of methanol decomposition catalytic activity and an increase in the area specific resistance for hydrogen electrooxidation.

Development of intermediate-temperature solid oxide fuel cells for direct utilization of hydrocarbon fuels

In this study, we compare the performance of solid oxide fuel cells (SOFC) having composite Cu-based anodes but made with the following low-temperature electrolytes: samaria-doped ceria (SDC), Sr- and Mg-doped lanthanum gallate (LSGM), and scandia-stabilized zirconia (ScSZ). Performance (V-I) curves and impedance spectra were measured using H 2 and n-butane fuels at 973 K. The results suggest that the use of electrolyte materials with higher ionic conductivity can lead to improved anodes for direct-utilization SOFC, although the performance of each of the cells in n-butane appears to be at least partially limited by the electrochemical oxidation reaction.

GDC-Based Low-Temperature SOFCs Powered by Hydrocarbon Fuels

The critical issues facing the development of economically competitive solid oxide fuel cell (SOFC) systems include lowering the operation temperature and creating novel anode materials and microstructures capable of efficiently utilizing hydrocarbon fuels. In this paper, we report our recent progress in developing more efficient anodes for direct utilization of methane and propane in low-temperature SOFCs. Anode-supported SOFCs with an electrolyte of 20 μm thick Gd-doped ceria (GDC) were fabricated by copressing, and both Ni- and Cu-based anodes were prepared by a solution impregnation process. Results indicate that both microstructure and composition of the anodes, as fabricated using a solution impregnation technique, greatly influence fuel cell performance. At 600°C, SOFCs fueled with humidified methane, and propane reach peak power densities of 602, 519, and 433 mW/cm2, respectively. © 2004 The Electrochemical Society. All rights reserved.

Measurement of electrode overpotentials for direct hydrocarbon conversion fuel cells

Cathodic and anodic overpotentials were measured using current interruption and AC impedance spectroscopy for two separate solid oxide fuel cells (SOFCs). The fuel cells used yttria-stabilized zirconia (YSZ) as the electrolyte, strontium-doped lanthanum manganite (LSM) as the cathode, and a porous YSZ layer impregnated with copper and ceria as the anode. The Cu/CeO 2/YSZ anode is active for the direct conversion of hydrocarbon fuels. Overpotentials measured using both current interruption and impedance spectroscopy for the fuel cell operating at 700 °C on both hydrogen and n-butane fuels are reported. In addition to providing the first electrode overpotential measurements for direct conversion fuel cells with Cu-based anodes, the results demonstrate that there may be significant uncertainties in measurements of electrode overpotentials for systems where there is a large difference between the characteristic frequencies of the anode and cathode processes and/or complex electrode kinetics.

Copper-Plated Stainless Steel for Bipolar Plates in Direct-Oxidation SOFC

The performance of copper-plated, stainless-steel plates, having an active area of 2.5x2.5 cm 2 square, was tested for use with an SOFC having a Cu-based anode for direct oxidation of n-butane at 973 K. In the absence of Cu, catastrophic carbon deposition, which rapidly caused blocking of the fuel channels, was observed due to reaction of the n-butane on the stainless steel. However, plating the fuel channels with Cu effectively prevented formation of large carbon deposits. After 24 hr operation in pure n-butane, the Cu plating effectively suppressed carbon deposition, except for the formation of tar-like substances formed by gas-phase thermal decomposition of the hydrocarbon. The tar-like substances were found to be soluble in toluene and could be analyzed by GC/MS, which showed that they were primarily poly-aromatic hydrocarbons having 2-6 aromatic rings.

Anodes for Direct Oxidation of Dry Hydrocarbons in a Solid-Oxide Fuel Cell

The manufacture of fuel cells that can operate directly on various hydrocarbon fuels, without the need for reforming, has the potential of greatly speeding the application of fuel cells for transportation and distributed-power applications. This paper will briefly review the literature in this area and describe recent developments in solid-oxide fuel cells (SOFCs) that demonstrate that direct-oxidation fuel cells are possible with Cu-based anodes. A new method for synthesizing thin-electrolyte, anode-supported cells is described that is based on tape casting with graphite pore formers (see Figure), followed by impregnation with aqueous solutions of Cu(NO3)2 and Ce(NO3)3. The performance of model SOFCs for direct conversion of n-butane and methane is shown. Finally, future developments that are needed for this technology to be commercialized are discussed.