Search

Protonic ceramic fuel cells (PCFCs) are one of the most efficient energy conversion devices. However, the performance of current PCFCs is greatly limited by the sluggish oxygen reduction reaction (ORR) kinetics and the fast degradation of the cathode due to contaminants poisoning (such as Cr species and steam). Here, a surface regulation of a double perovskite PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF) cathode by a Pr0.9Fe0.7Co0.3O3 (PFC) catalyst coating to enhance the ORR activity and stability is reported. When tested in direct contact with Cr in the air with 3% H2O at 650 °C, the polarization resistance (Rp) of the PFC coated PBSCF (PFC‐PBSCF) electrode increases from ≈0.39 to 0.45 Ω cm2 after 100 h operation; in contrast, the Rp of a PBSCF electrode increases from 0.63 to 0.82 Ω cm2. Further, a PCFC with the PFC‐PBSCF cathode demonstrates an excellent peak power density (≈1.08 W cm–2 at 650 °C) and significantly enhanced durability (degradation rate of 0.03% h−1), much better than those of the cells with a PBSCF cathode (≈0.75 W cm–2 and degradation rate of 0.12% h−1). Raman spectroscopy and density functional theory calculations indicate that the PFC catalyst coating diminishes the formation of Cr species, such as (Ba1‐xSrx)CrO4, on the cathode surface. [ABSTRACT FROM AUTHOR]

The development of active and durable air electrodes is of great significance to the maturity of reversible protonic ceramic electrochemical cells (R‐PCECs). This article reports the recent findings in the performance enhancement of R‐PCECs using a novel heterostructured air electrode, consisting of a double perovskite PrBaCo1.6Fe0.2Nb0.2O5+δ backbone covered with in situ exsolved nanoparticles of Nb‐deficient PrBaCo1.6Fe0.2Nb0.2−xO5+δ. Such a heterostructured electrode is induced by the benign interaction of the electrode and steam during the cell operation, showing a faster surface exchange process, as confirmed by a mapping of high‐angle annular dark‐field transmission electron microscopy image, and distribution of relaxation time analyses of the electrochemical impedance spectra. The in situ formed Nb‐deficient nanoparticles and Nb‐rich parental perovskite significantly enhance the catalytic activity and durability of the air electrode toward oxygen reduction/evolution reaction on single cells at 650 °C, achieving a peak power density of 1.059 W cm−2 in fuel cell mode, a current density of 2.148 A cm−2 at 1.3 V in electrolysis cell mode, and good durability of a cycling test at ±0.5 A cm−2 for 200 h in dual modes of fuel cell and electrolysis cell. [ABSTRACT FROM AUTHOR]

Reversible protonic ceramic electrochemical cells (R-PCECs) are ideally suited for efficient energy storage and conversion; however, one of the limiting factors to high performance is the poor stability and insufficient electrocatalytic activity for oxygen reduction and evolution of the air electrode exposed to the high concentration of steam. Here we report our findings in enhancing the electrochemical activity and durability of a perovskite-type air electrode, Ba0.9Co0.7Fe0.2Nb0.1O3-δ (BCFN), via a water-promoted surface restructuring process. Under properly-controlled operating conditions, the BCFN electrode is naturally restructured to an Nb-rich BCFN electrode covered with Nb-deficient BCFN nanoparticles. When used as the air electrode for a fuel-electrode-supported R-PCEC, good performances are demonstrated at 650 °C, achieving a peak power density of 1.70 W cm−2 in the fuel cell mode and a current density of 2.8 A cm−2 at 1.3 V in the electrolysis mode while maintaining reasonable Faradaic efficiencies and promising durability. One limiting factor to the high-performing reversible protonic ceramic electrochemical cells is the poor stability and electrocatalytic activity of air electrodes. Here the authors report a water-promoted surface restructuring process to enhance the performance of Ba0.9Co0.7Fe0.2Nb0.1O3-δ air electrode. [ABSTRACT FROM AUTHOR]

Abstract: Composite cathodes of solid oxide fuel cells (SOFCs) are normally fabricated by mechanical mixing of electronic‐ and ionic‐conducting phases. Here, a dual‐phase SOFC cathode, composed of perovskite PrNi0.5Mn0.5O3 (PNM) and exsoluted fluorite PrOx particles, produced in situ through a glycine–nitrate solution combustion process, is reported. When applied as the cathode for a BaZr0.1Ce0.7Y0.1Yb0.1O3‐based protonic ceramic fuel cell, the hybrid cathode displays excellent electrocatalytic activity (area‐specific resistance of 0.052 Ω cm2 at 700 °C) and remarkable long‐term stability when operated at a cell voltage of 0.7 V for ≈500 h using H2 as fuel and ambient air as oxidant. The excellent performance is attributed to the proton‐conducting BaPrO3‐based coating and high‐concentration oxygen vacancies of a Ba‐doped PNM surface coating, produced by the reaction between the cathode and Ba from the electrolyte (via evaporation or diffusion), as confirmed by detailed X‐ray photoelectron spectroscopy, Raman spectroscopy, and density functional theory‐based calculations. [ABSTRACT FROM AUTHOR]

(La0.6Sr0.4)0.95Co0.2Fe0.8O3+δ nanofiber cathode prepared by electrospinning demonstrates excellent oxygen reduction reaction (ORR) activity, as reflected by reduced polarization resistance and diminished activation energy. ORR enhancement can be attributed to the efficient mass/charge transfer. Further, the nanofiber electrode shows good durability under operation conditions of solid oxide fuel cells. [ABSTRACT FROM AUTHOR]

Lithium titanate (Li4Ti5O12) and SiO2-incorporated Li4Ti5O12 are synthesized, using a facile cellulose-assisted combustion technique, as anodes for lithium-ion batteries tested under different conditions, i.e., discharge to an end potential of 1.0 V/0.01 V at room/elevated temperature (55 °C). The particles are characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), nitrogen adsorption–desorption isotherms, X-ray spectrometry (EDX) and transmission electron microscopy (TEM). The results show that silicon element is successfully incorporated with Li4Ti5O12 homogeneously in the forms of Si-doping and SiO2 separate phase. When discharged in the potential range of 0.01–3.0 V, initial discharge capacities of 260 mA h g−1 and 298 mA h g−1 are obtained for the Li4Ti5O12 and SiO2-incorporated Li4Ti5O12 electrodes, respectively. Both electrodes show stable cycling performance for 400 cycles (approximately 1.5 months) at room temperature between 0.01 and 3.0 V at a current density of 175 mA g−1. In addition, the stability of the electrodes under hurdle conditions (0.01–3.0 V at 55 °C) are explored and discussed, and a proposed mechanism for the “decrease–increase–decrease” cycling behavior is confirmed using electrochemical impedance spectroscopy (EIS) and TEM observations. The incorporation of SiO2 was found to improve the cycling stability under hurdle conditions. [ABSTRACT FROM AUTHOR]

The development of high-performance supercapacitors (SCs) often faces some contradictory and competing requirements such as excellent rate capability, long cycling life, and high energy density. One effective strategy is to explore electrode materials of high capacitance, electrode architectures of fast charge and mass transfer, and electrolytes of wide voltage window. Here we report a facile and readily scalable strategy to produce high-performance N-doped graphene with a high specific capacitance (∼390 F g −1 ). A symmetric SC device with a wide voltage window of 3.5 V is also successfully fabricated based on the N-doped graphene electrode. More importantly, the as-assembled symmetric SC delivers a high energy density of 55 Wh kg −1  at a power density of 1800 W kg −1 while maintaining superior cycling life (retaining 96.6% of the initial capacitance after 20,000 cycles). Even at a power density as high as 8800 W kg −1 , it still retains an energy density of 29 Wh kg −1 , higher than those of previously reported graphene-based symmetric SCs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Improvement of electrochemical stability by doping Nb. • Enhancement of electrocatalytic activity by tuning Ba deficiency. • Peak power density of 1.5 and 1.0 W cm−2 at 600 °C for GDC and BZCYYb single cells. • Continuous operation of electrolysis cell for 1,000 h with minimal degradation. Solid oxide cells (SOCs) are considered the most efficient system for reversible conversion between chemical and electrical energy, thus having potential to be an attractive technology for a sustainable energy future. To achieve high round-trip efficiency, highly efficient and durable air electrode materials are needed to minimize energy loss associated with oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Here we report a bi-functional air electrode material, PrBa 0.9 Co 1.96 Nb 0.04 O 5+δ , demonstrating outstanding electrochemical performance (e.g., achieving peak power densities of over 1.5 and 1 W cm−2, respectively, for Gd 0.1 Ce 0.9 O 1.95 and BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-δ based fuel cells at 600 °C) while maintaining excellent stability (e.g., having a degradation rate of 40 mV per 1,000 h for H 2 O electrolysis cells). The excellent property of the new electrode is attributed to the improved stability from Nb doping and the enhanced electrocatalytic activity from tuning Ba deficiency, as confirmed by experimental results and computational analysis. [ABSTRACT FROM AUTHOR]