Cobalt-free Cathode Research Articles

Breaking Free from Cobalt Reliance in Lithium-Ion Batteries.

SummaryThe exponential growth in demand for electric vehicles (EVs) necessitates increasing supplies of low-cost and high-performance lithium-ion batteries (LIBs). Naturally, the ramp-up in LIB production raises concerns over raw material availability, where constraints can generate severe price spikes and bring the momentum and optimism of the EV market to a halt. Particularly, the reliance of cobalt in the cathode is concerning owing to its high cost, scarcity, and centralized and volatile supply chain structure. However, compositions suitable for EV applications that demonstrate high energy density and lifetime are all reliant on cobalt to some degree. In this work, we assess the necessity and feasibility of developing and commercializing cobalt-free cathode materials for LIBs. Promising cobalt-free compositions and critical areas of research are highlighted, which provide new insight into the role and contribution of cobalt.

PrSr3Fe3O10−δ as cobalt-free cathode for intermediate-temperature solid oxide fuel cell

In this work, we investigate cobalt-free Ruddlesden Popper oxide with the nominal composition of PrSr3Fe3O10−δ (PSF) as potential cathode for intermediate temperature solid oxide fuel cells based on Ce0.8Sm0.2O1.9 (SDC) electrolyte. It is found that PSF is chemically compatible with the SDC for temperatures up to 1000 °C. The average thermal expansion coefficient of PSF in air is 16.5 × 10−6 K−1 in a temperature range of 30–1000 °C, and its electrical conductivity reaches the maximum value of 98 S cm−1 at 500 °C. The area specific resistance of PSF is 0.075 Ω cm2 at 800 °C. Peak power density of 405 mW cm−2 is achieved with PSF at 800 °C.

Lithium-ion batteries go cobalt-free

Lithium-ion battery cathodes have always relied on cobalt, but the expensive metal’s supply chain is fraught with issues. A new cobalt-free cathode could provide reprieve ( 2020, DOI: ). In lab tes...

Inhibition of transition metals dissolution in cobalt-free cathode with ultrathin robust interphase in concentrated electrolyte

The low Coulombic efficiency during cycling hinders the application of Cobalt-free lithium-rich materials in lithium-ion batteries. Here we demonstrated that the dissolution of iron, rather than traditionally acknowledged manganese, is mainly responsible for the low Coulombic efficiency of the iron-substituted cobalt-free lithium-rich material. Besides, we presented an approach to inhibit the dissolution of transition metal ions by using concentrated electrolytes. We found that the cathode electrolyte interphase (CEI) layer formed in the concentrated electrolyte is a uniform and robust LiF-rich CEI, which is a sharp contrast with the uneven and fragile organic-rich CEI formed in the dilute electrolyte. The LiF-rich CEI not only effectively inhibits the dissolution of TMs but also stabilizes the cathode structure. The Coulombic efficiency, cycling stability, rate performance, and safety of the Fe-substituted cobalt-free lithium-rich cathode material in the concentrated electrolyte have been improved tremendously.

A novel BaFe0.8Zn0.1Bi0.1O3−δ cathode for proton conducting solid oxide fuel cells

Cobalt-free materials with triple conductivity are considered potential cathode materials for solid oxide fuel cells (SOFC). We applied Zn to improve the hydration ability and redox activity of a traditional barium-ferrite (BFO) cathode, in order to improve the performance of the proton conductor-based SOFC (H-SOFC). Evidence suggests that the performance of BFO cathode is improved by Zn-doping. The single cell with BaFe0.8Zn0.1Bi0.1O3−δ (BFZB) as the cathode can achieve 816.26 mW cm−2 at 700 °C after Zn-doping. Coupled with the impregnation method, cell performance with BFZB nanoparticles as the cathode was further improved to 1138.21 mW cm−2 at 700 °C. The new cobalt-free cathode has excellent performance, which is even comparable to that of some cobalt-containing cathodes and thus worthy of further investigations.

Effect of Na Doping or Substitution on the Structural and Electrochemical Properties of Cobalt-Free Li-Rich Mn-Based Cathode Materials

Cobalt-free Li-rich Mn-based cathode materials are considered to be the next generation of Li-ion batteries due to low cost, high discharge capacities and high safety feature. However, there are still several serious issues that need to be solved urgently, such as low initial coulombic efficiency, low rate capability, poor cycling performance and voltage fading. Na doping or substitution is introduced to improve the electrochemical performance of Li1.2Mn0.6Ni0.2O2 cathode material, which is synthesized by sol-gel method. The effect of Na doping or substitution on the morphological, structural and electrochemical properties was systematically studied and analyzed by scanning electron microscope (SEM), X-Ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cell test system and electrochemical workstation. These results illustrate that lattice layer spacing is enlarged by Na doping or substitution, which is beneficial for the diffusion of Li-ion, and the voltage fading is successfully suppressed. The best electrochemical properties were obtained when Na doping, which is attributed to the stronger structural stability and better reversibility of Li+ during the initial charge and discharge process.

Research advances on cobalt-free cathodes for Li-ion batteries - The high voltage LiMn1.5Ni0.5O4 as an example

LiMn1.5Ni0.5O4 is one of the most promising cathode materials for use in either next generation lithium-ion batteries or all solid-state batteries. However, despite the significant Research and Development (R&D) carried out throughout the last two decades the material has not made serious inroads into market. One of the major reasons is the lack of consistency in the reported intrinsic properties and electrochemical performance owing to major controversies in synthesis, crystal structure and bulk and interfacial properties of LiMn1.5Ni0.5O4, notably in contact with electrolytes. This paper is a compelling review providing an assessment on the mainstream R&D dealing with the various crystal structures of LiMn1.5Ni0.5O4 and their evolutions observed during synthesis and cycling in correlation with their electrochemical performance. Influence of electrolytes and additives along with modifications through doping and surface treatments are interrelated, and the electronic and ionic transport properties of the ordered and disordered LiMn1.5Ni0.5O4 phases are discussed. Overall, this review provides a detailed assessment on LiMn1.5Ni0.5O4 and the underlying mechanisms governing its electrochemical performance broadly providing a focused framework for further advancement towards commercialization.

Ionic Liquid Electrolytes Enabling the Development of Highly Efficient High-Voltage Potassium-Ion Full Cells with a Potassium Manganese Hexacyanoferrate Cathode

Potassium-ion (K-ion) batteries are a promising complementary technology to lithium-ion in which less scarce and less expensive elements can be used; potassium instead of lithium, aluminum instead of copper, and cobalt-free cathodes. They have the advantage over sodium-ion batteries in that graphite, the standard commercial anode for lithium-ion, can be used[1] and potassium has a lower reduction potential (K+/K) than that of sodium and even lithium. Currently, the research focus is on developing energy-dense, high-voltage cathode materials. Prussian blue analogues, with their open-framework structure, are well-suited to reversibly insert the relatively large potassium ion.[2] Potassium manganese hexacyanoferrate (KMF) is of particular interest due to its high theoretical capacity (155 mAh g-1) and high voltage (around 4 V vs. K+/K) making it one of the most promising K-ion candidate cathode materials.[3] However, significant challenges remain before KMF K-ion batteries are suitable for commercialization. Current collector corrosion at high voltages and material instability lead to low coulombic efficiency on cycling and severe capacity fade.[4]In this work we report a significant improvement in KMF electrode performance by utilizing a highly stable ionic liquid electrolyte. This electrolyte suppresses corrosion of the current collector and deleterious reactions on the cathode. Performance of the KMF material is significantly controlled by its composition and particle size, which can be controlled during synthesis. We employ high-throughput techniques to systematically study a wide synthesis parameter space in order to minimize hexacyanoferrate vacancy and water content whilst controlling for particle size. We found that changing particle size considerably impacted specific capacity and cyclability, and a compromise must be made. Our optimized KMF material had a specific capacity of 119 mA h g-1, a coulombic efficiency of 99.3%, and relatively good cyclability. Crucially, graphite also displayed excellent electrochemical performance in the same ionic liquid electrolyte (maintaining 99% of initial capacity after 400 cycles and a coulombic efficiency of more than 99.9%) and exhibited a highly reversible electrode reaction studied by in operando XRD. Optimized KMF | ionic liquid electrolyte | graphite full-cell chemistry reported here proves a viable strategy for highly efficient high-voltage potassium-ion batteries.[1] Komaba et al., Potassium intercalation into graphite to realize high-voltage/high-power potassium-ion batteries and potassium-ion capacitors, Electrochemistry Communications (2015), 60, 172-175[2] Hurlbutt et al., Prussian Blue Analogs as Battery Materials, Joule (2018), 2, 10, 1950-1960[3] Bie et al., A novel K-ion battery: hexacyanoferrate(II)/graphite cell, J. Mater. Chem. A (2017), 5, 9, 4325-4330[4] Hosaka et al. Highly concentrated electrolyte solutions for 4 V class potassium-ion batteries, Chem. Commun. (2018), 54, 8387-8390

Advanced 18650 Lithium-Ion Batteries with LiMn2O4@Carbon Core-Shell Cathode and Si/Mcmb Anode

Nowadays, the 18650 cylindrical cells of lithium-ion batteries using cobalt-containing cathode materials have currently produced with a purpose of operating source of electric-powered application such as electric vehicle (EV), hybrid electric vehicle (HEV), and small-scale energy storage system (ESS). However, cobalt is not abundant and expensive. Thus, cobalt-free cathode materials are of interest. In this work, 18650 lithium-ion battery using LiMn2O4/Carbon core-shell (LMO@C) cathode and Si/MCMB anode. The LMO@C materials was synthesized bya sonvent-free mechanofusion method with a highly uniform coating. The LMO particles with fully covered by carbon nanoparticles can exhibit higher capacity ca. 10-15% as compared with the pristine LMO.In addition, the LMO@C also presents the superb rate capacity retention as well as cycling stability due to the improved intrinsic conductivity and mechanical property.

Mixed proton–electron–oxide ion triple conducting manganite as an efficient cobalt-free cathode for protonic ceramic fuel cells

Cubic La0.7Sr0.3Mn1−xNiyO3−δ undergoes the hydration reaction with the charge disproportionation between Mn and O atoms, and thus, can reduce the interfacial polarization of protonic solid oxide cells due to the H+/O2−/e− triple conductivity.

High capacity Li/Ni rich Ni-Ti-Mo oxide cathode for Li-ion batteries

With the rising cost and insufficient supply of cobalt, the thrust for cobalt-free cathode materials with the high specific capacity to build Li-ion batteries has increased significantly. Using nickel as the prime electrochemical active species, we have synthesized a new-class of materials with the combination of ordered and disordered phases. To obtain high capacity and electrical charge neutrality, stoichiometry of cations designed in a way that it forms Li/Ni rich Ni-Ti-Mo oxide materials. In addition to conventional capacity from redox activity of transition metals, partially reversible oxygen redox reaction also contributes to electrochemical activity and thus results in unusual high capacity. The resultant cathode materials of LiNi0.5Ti0.5O2-(Li4MoO5)0.8 and LiNiO2 mixture phases reach the specific capacity of 240 mAh/g. Detailed soft X-ray absorption spectroscopy and electron microscopy are used to reveal the crystal phases in this system and trace changes in the Ni2+/Ni4+ redox couple during charge-discharge processes. Such comprehensive analysis of ordered-disordered oxides suggesting potentiality to develop high-capacity cobalt-free cathodes.

Cobalt-free perovskite Ln0.5Sr0.5Fe0.8Cu0.2O3-δ (Ln = Pr, Nd, Sm, and Gd) as cathode for intermediate-temperature solid oxide fuel cell

Ln0.5Sr0.5Fe0.8Cu0.2O3-δ (LnSFC, Ln = Pr, Nd, Sm, Gd) perovskite oxide as a cobalt-free cathode was systematically evaluated for intermediate-temperature solid oxide fuel cell (IT-SOFC). XRD results show that PrSFC presents the cubic structure, while NdSFC, SmSFC, and GdSFC present an orthorhombic structure. The conductivity of the four samples is in accordance with the GdSFC < SmSFC < NdSFC < PrSFC relationship. AC impedance testing was performed using a symmetrical fuel cell of the structure LnSFC/Ce0.9Sm0.1O1.95(SDC)/LnSFC. The polarization resistance values of PrSFC, NdSFC, SmSFC, and GdSFC are 0.036, 0.089, 0.097, and 0.160 Ω cm2 at 800 °C, respectively. Then, SDC electrolyte-support single cell was fabricated and the power densities of PrSFC, NdSFC, SmSFC, and GdSFC cathodes were 364, 311, 254 and 104 mW cm−2, respectively, at 800 °C. Our preliminary experiment results show that LnSFC oxide meets the requirements of the electrode, and it can be a possible cathode for IT-SOFC.

(Invited) Low-Cobalt and Cobalt-Free Cathodes for Next-Generation Lithium-Ion Batteries

Lithium-ion batteries have become an integral part of our daily life with an exponential growth in portable electronics during the past couple of decades. They are now being intensively developed for the electrification of the transportation sector. They also have the potential to penetrate into the utility industry for the grid storage of electricity produced from renewable sources like solar and wind. As we move from small batteries used in portable devices to large batteries used in electric vehicles and grid storage, cost becomes a major factor in addition to other factors like cycle life, safety, energy density, charge-discharge rate, and environmental impact. Lithium-ion batteries for portable devices and electric vehicles currently employ layered LiNi1-x-yMnxCoyO2 cathodes with a significant amount of cobalt. Unfortunately, cobalt has limited abundance and is expensive, which could pose serious problems for a widespread deployment of lithium-ion batteries for electric vehicles and grid storage. Therefore, it is critical to develop cathodes with low-cobalt content or no-cobalt. Accordingly, the presentation will focus on the design and development of low-cobalt and cobalt-free layered oxide cathodes for next-generation lithium-ion batteries. Layered LiNi1-x-yMnxCoyO2 cathodes with cobalt content as low as 6% for M in LiMO2 or no cobalt are synthesized with a desired optimum particle size by a coprecipitation of the hydroxide precursors employing a tank reactor. The hydroxide precursors are then fired at desired temperatures with lithium hydroxide with or without appropriate dopants to obtain the layered LiMO2 oxides. After an in-depth characterization, the oxide cathodes are evaluated by pairing with graphite anodes in full lithium-ion cells. Both the oxide cathodes and graphite anodes are characterized with a suite of analytical techniques before and after cycling the full cells for thousands of cycles to develop a fundamental understanding of the factors that lead to performance degradation. The analytical techniques include in-situ X-ray diffraction, X-ray photoelectron spectroscopy, time of flight secondary ion mass spectrometry, scanning electron microscopy, and high-resolution transmission electron microscopy. Extensive data on cathode compositions, such as LiNi0.94Co0.06O2 and LiNiO2 with and without doping will be presented. Furthermore, the thermal stability and air-stability of the samples and the effects of doping on them will be discussed. Stabilized cathode compositions with capacities as high as 220 mA h g-1 and long cycle life will be presented.

(Invited) Towards the Realization of Sustainable High-Performance Lithium-Ion Batteries: Aqueous Processing of Cobalt-Free High-Energy Cathodes

The recently rising awareness for a more sustainable cell manufacturing can be expected to gain even more momentum in sight of the announcements from major car manufacturers across Europe and North America to entirely electrify their fleet within the next half-decade1,2. The implementation of aqueous electrode processing strategies for lithium-ion cathodes is a key step to realize the environmentally benign battery production. To achieve this ambitious goal, most studies focus on the development of non-toxic and abundant active materials and specifically, the implementation of nature-derived, inexpensive binders in combination with the use of water as dispersion agent and solvent provides the great possibility to spare energy-intensive drying procedures and costly dry-room conditions, and thus, will turn the whole battery fabrication more eco-efficient 3,4. What could easily be established for graphite anodes – employing water-soluble natural polymers as binder, thus, abolishing the need of toxic and rather costly N-methyl-2-pyrrolidone (NMP) as processing solvent3,5 – appears more complicated for transition metal oxide-based and imperatively cobalt-free cathode materials, which suffer from lithium leaching and transition metal dissolution when getting in contact with water, which has, so far, rendered the use of aqueous binders very challenging6,7. In our group we recently demonstrated the general feasibility for the aqueous processing of several lithium-ion cathode materials, such as high-voltage LiNi0.5Mn1.5O4, by introducing a complementary approach, of suitable processing additives to stabilize the active material surface as well as the electrode/electrolyte/current collector interface8. Moreover, we extended our investigations to various binder systems and cathode materials in order to advance the aqueous electrode preparation and move from the well-established lab-scale process towards the fabrication of commercial-scale lithium-ion batteries9. References C. J. Barnhart and S. M. Benson, Energy Environ. Sci., 6, 1083 (2013).D. Larcher and J. M. Tarascon, Nat. Chem., 7, 19–29 (2015).D. Bresser, D. Buchholz, A. Moretti, A. Varzi, and S. Passerini, Energy Environ. Sci. (2018) http://xlink.rsc.org/?DOI=C8EE00640G.A. Kwade et al., Nat. Energy, 3, 290–300 (2018) http://www.nature.com/articles/s41560-018-0130-3.S. F. Lux, F. Schappacher, A. Balducci, S. Passerini, and M. Winter, J. Electrochem. Soc., 157, A320 (2010).M. M. Thackeray, J. Am. Ceram. Soc., 82, 3347–3354 (1999).N. Loeffler et al., ChemSusChem, 9, 1112–1117 (2016).M. Kuenzel et al., ChemSusChem, 11, 562–573 (2018).A. Kazzazi et al., ACS Appl. Mater. Interfaces, 10, 17214–17222 (2018).

Enhancing Oxygen Reduction Reaction Activity and CO2 Tolerance of Cathode for Low-Temperature Solid Oxide Fuel Cells by in Situ Formation of Carbonates.

Development of low-cost and cobalt-free efficient cathode materials for oxygen reduction reaction (ORR) remains one of the paramount motivations for material researchers at a low temperature (<650 °C). In particular, iron-based perovskite oxides show promise as electrocatalysts for ORR because Fe metal is cheaper and naturally abundant, exhibit matched thermal expansion with contacting components such as electrolytes, and show high tolerance in a CO2-containing atmosphere. Herein, we demonstrated a new mechanism, the in situ formation of alkali metal carbonates at the cathode surface. This new mechanism leads to an efficient and robust cobalt-free electrocatalyst (Sr0.95A0.05Fe0.8Nb0.1Ta0.1O3-δ, SAFNT5, A = Li, Na, and K) for the application of low-temperature solid oxide fuel cells (LT-SOFCs). Our results revealed that the formation of Li\K carbonates boosts the ORR activity with an area-specific resistance as low as 0.12 and 0.18 Ω cm2 at 600 °C, which show the highest performance of the cobalt-free single-phase cathode that has been ever reported so far. We also find that the chemical stability and tolerance of tested cathodes toward CO2 poisoning significantly improved with alkali carbonates, as compared to the pristine SrFe0.8Nb0.1Ta0.1O3-δ (SFNT) at 600 °C. This work demonstrates the conclusive role of alkali carbonates in developing highly efficient and stable cobalt-free cathodes for LT-SOFCs and CO2 neutralization.

Enhanced electrocatalytic activity and CO2 tolerant Bi0.5Sr0.5Fe1-Ta O3- as cobalt-free cathode for intermediate-temperature solid oxide fuel cells

Abstract One of the significant motivations in developing intermediate-temperature solid oxide fuel cells (IT-SOFCs) is to design cobalt-free cathodes with high electrocatalytic activity and CO 2 tolerance ability. In this work, iron-based perovskite materials Bi 0.5 Sr 0.5 Fe 1- x Ta x O 3- δ are investigated as potential cathodes for IT-SOFCs. The effects of Ta doping on crystal structure, thermal expansion coefficients and electrocatalytic activities are systematically evaluated. Among the Ta-doped oxides, Bi 0.5 Sr 0.5 Fe 0.9 Ta 0.1 O 3- δ exhibits the highest electrochemical performance with the lowest polarization resistance ( R p ) of 0.124 Ω cm 2 at 700 °C in air. The peak power density of the single cell with Bi 0.5 Sr 0.5 Fe 0.9 Ta 0.1 O 3- δ cathode reaches 1.36 W cm −2 at 700 °C. Compared to Bi 0.5 Sr 0.5 FeO 3- δ , the improved CO 2 tolerance of Ta-doped oxides can be attributed to the high acidity of Ta 5+ cations and the increased average metal bond energy (ABE) within the material. Further study proves that the adsorption-dissociation process of molecular oxygen is the limiting step for oxygen reduction reaction (ORR) on Bi 0.5 Sr 0.5 Fe 0.9 Ta 0.1 O 3- δ cathode.

Influence of layer numbers on the structural and electrical performance of cobalt-free SrFe0.5Ti0.5O3-δ cathode for ntermediate-temperature solid oxide fuel cell application

The influence of layer numbers on the structural and electrical performance of SrFe0.5Ti0.5O3-δ cobalt-free cathode was studied. The SrFe0.5Ti0.5O3-δ cathode films fabricated using screen-printing technique with different layer numbers sintered at 1300 °C for 2 h were characterised using field-emission scanning electron microscopy (FESEM) for structural analysis and four-point van der Pauw method for direct current electrical conductivity (σDC). FESEM micrographs confirmed that the SrFe0.5Ti0.5O3-δ cobalt-free cathode films (fabricated with different layer numbers) adhered well on the samarium doped ceria electrolyte surface. The porous films were also uniform without crack formation. The thicknesses of the as-fabricated cathode films were 9.0 ± 0.5, 25.6 ± 1.0, 54 ± 0.6, 71.2 ± 1.4 and 92.2 ± 1.6 μm for layer numbers 1 (1×), 4, 7, 10 and 13 times (13×), respectively. The electrical performance of SrFe0.5Ti0.5O3-δ cobalt-free cathodes was reported within the operating temperature ranging from 550 °C to 800 °C as the targeted application was the intermediate temperature solid oxide fuel cell. The layer numbers (thickness) dependence of σDC suggested a mechanism of long electron pathway at the surface and through the films due to the increase in pores. While the sintering temperature is kept constant, increasing in the number of layers increased the pores accordingly. Hence, the lowest σDC value at 800 °C (2.45 S cm−1) is obtained for SrFe0.5Ti0.5O3-δ cathode films with high number of layers (13×). The highest σDC value (16.46 S cm−1) was recorded for a single layer (1×) SrFe0.5Ti0.5O3-δ cathode film. Although the conductivity value was still far from the desired theoretical conductivity of 100 S cm−1, this result was better than that of the literature that reported the same composition, thereby showing that the quality of cathode film was improved.

Structural, morphological, and electrochemical behavior of titanium-doped SrFe1-xTixO3-δ (x = 0.1–0.5) perovskite as a cobalt-free solid oxide fuel cell cathode

Abstract Titanium, Ti-doped SrFe1-xTixO3-δ (x = 0.1–0.5) perovskite-structured ceramics were synthesized via solution combustion. The structural, morphological, and electrochemical behaviors of the as-synthesized materials were investigated to determine the applicability of SrFe1-xTixO3-δ as a cobalt-free cathode material for intermediate-temperature solid oxide fuel cells. X-ray diffraction analysis confirmed the formation of a single-phase cubic perovskite structure. The unit volume of this perovskite structure increased as the amount of Ti dopant increased. Morphological analysis revealed that the porosity of the SrFe1-xTixO3-δ perovskite cathode film was inversely proportional to the amount of Ti dopant. The cathode SrFe0·9Ti0·1O3-δ film exhibited a high porosity of 24.74 ± 0.52%, a low but acceptable hardness value of 0.70 ± 0.01 GPa and an area specific resistance of 0.57 Ω cm2. These results suggested that cobalt-free SrFe1-xTixO3-δ cathode was still not good enough to be compared with the existing cobalt-containing cathode such as lanthanum strontium cobalt ferrite. But, the results obtained from this work can be considered as a major turning point as the literature works on SrFe1-xTixO3-δ cathode showed excellence electrochemical performance. The contradict result between the present and past studies proved that the use of SrFe1-xTixO3-δ cathode is worthy of being studied into details to confirm its capability.

A novel anions and cations co-doped strategy for developing high-performance cobalt-free cathode for intermediate-temperature proton-conducting solid oxide fuel cells

The sluggish activity of cathode at intermediate-temperature limits commercialization of proton-conducting solid oxide fuel cells (H-SOFCs). In this investigation, a novel cathode of Ba0.95Ca0.05Fe0.85Sn0.05Y0.1O2.9−δF0.1 was successfully developed by co-doping of anion F and cations Ca, Sn, Y. We studied the effect of F−-doping on phase structure, electrical conductivity and electrochemical properties of the cell. Compared with Ba0.95Ca0.05Fe0.85Sn0.05Y0.1O3−δ, F−-doped Ba0.95Ca0.05Fe0.85Sn0.05Y0.1O3−δ exhibited higher conductivity. Composite cathode consisting of Ba0.95Ca0.05Fe0.85Sn0.05Y0.1O2.9−δF0.1 and Sm0.2Ce0.8O2−δ was applied in H-SOFCs with BaZr0.1Ce0.7Y0.2O3−δ electrolyte which achieves an encouraging performance with the maximum power density of 1050 mW cm−2 and polarization resistance of 0.04 Ω cm2 at 700 °C. The result of First-principles calculations based on spin-polarized Density Functional Theory shows that doping of F− reduces the activation energy required for migration of oxygen ions. These results demonstrate that the anions and cations co-doped strategy can provide a new horizon for the cathode in H-SOFCs.

High performance BaCe0.5Fe0.5-xBixO3-δ as cobalt-free cathode for proton-conducting solid oxide fuel cells

To explore the space for further optimization of BaCeO3-based single-phase cathode, series of perovskite materials BaCe0.5Fe0.5-xBixO3-δ (x = 0, 0.1, 0.2, 0.3) as cobalt-free cathodes for proton conducting solid oxide fuel cells are evaluated in this assignment. The influence of the firing temperature on cathode microstructures and the electrochemical performance of fuel cells is evaluated, which states clearly that the best sintering temperature for BaCe0.5Fe0.3Bi0.2O3-δ cathode is 900 °C. Moreover, a special attention is paid to the effect of the Bi doping amount on the phase structure and electrochemical performance. With the cathode BaCe0.5Fe0.3Bi0.2O3-δ, the single cell achieves the polarization resistance of 0.061 Ω cm2 and the maximum power density of 943 mW cm−2 at 700 °C. These encouraging electrochemical results demonstrate that BaCe0.5Fe0.3Bi0.2O3-δ is a promising cobalt-free cathode for proton-conducting solid oxide fuel cells.