In situ tailored nickel nano-catalyst layer for internal reforming hydrocarbon fueled SOFCs

The authors gratefully thank the Engineering and Physical Sciences Research Council (EPSRC) SuperGen Hydrogen Fuel Cells Challenges Flame SOFC Project (Grant No EP/K021036/1) for financial supportConventional Ni cermet anodes suffer from carbon deposition when they are directly used with hydrocarbon fuels due to the negative effects of pyrolysis and Boudouard reactions. In this work, the use of a non-stoichiometric perovskite, La0.8Ce0.1Ni0.4Ti0.6O3, as a reforming layer in reducing atmospheres led to the surface being highly populated with homogeneously exsolved Ni nano particles. This catalyst layer was applied to Ni-GDC anode supported and ScSZ electrolyte supported cells to prevent carbon deposition and to stabilize operation with dry methane. The catalyst layer showed both excellent attachment to the Ni-GDC anode and resistance to carbon deposition. The performance of the Ni-GDC anode-supported cells with the catalyst layer was about 1.1 W/cm2 in hydrogen fuel which is similar to that seen without the use of a catalyst layer. For the ScSZ electrolyte supported cells, the catalyst layer improved the power density and stability when in operation with dry methane.Publisher PD

Ethanol internal reforming in solid oxide fuel cells: A path toward high performance metal-supported cells for vehicular applications

Internal reforming of ethanol fuel was investigated on high-performance metal-supported solid oxide fuel cells (MS-SOFCs) with infiltrated catalysts. The hydrogen concentration and internal reforming effects were evaluated systematically with different fuels including: hydrogen, simulated reformate, anhydrous ethanol, ethanol water blend, and hydrogen-nitrogen mixtures. A simple infiltration of Ni reforming catalyst into 40 vol% Ni-Sm0.20Ce0.80O2-δ (Ni-SDCN40) and fuel-side metal support leads to complete internal reforming, as confirmed by comparison to simulated reformate. The performance difference between hydrogen and fully-reformed ethanol is attributed entirely to decrease in hydrogen concentration. High peak power density was achieved for a range of conditions, for example 1.0 W cm−2 at 650 °C in ethanol-water blend, and 1.4 W cm−2 at 700 °C in anhydrous ethanol fuel. Initial durability tests with ethanol-water blend show promising stability for 100 h at 700 °C and 0.7 V. Carbon is not deposited in the Ni-SDCN40 anode during operation

Fundamentals of electro- and thermochemistry in the anode of solid-oxide fuel cells with hydrocarbon and syngas fuels

Abstract High fuel flexibility of solid-oxide fuel cells (SOFCs) affords the possibility to use relatively cheap, safe, and readily available hydrocarbon (e.g., CH₄) or coal syngas (i.e., CO-H₂ mixtures) fuels. Utilization of such fuels would greatly lower fuel cost and increase the feasibility of SOFC commercialization, especially for near-term adoption in anticipation of the long-awaited so-called “hydrogen economy”. Current SOFC technology has shown good performance with a wide range of hydrocarbon and syngas fuels, but there are still significant challenges for practical application. In this paper, the basic operating principles, state-of-the-art performance benchmarks, and SOFC-relevant materials are summarized. More in-depth reviews on those topics can be found in Kee and co-workers [Combust Sci and Tech 2008; 180:1207–44 and Proc Combust Inst 2005; 30:2379–404] and McIntosh and Gorte [Chem Rev 2004; 104:4845–65]. The focus of this review is on the fundamentals and development of detailed electro- and thermal (or simply, electrothermal) chemistry within the SOFC anode, including electrochemical oxidation mechanisms for H₂, CO, CH₄, and carbon, as well as the effects of carbon deposition and sulfur poisoning. The interdependence of heterogeneous chemistry, charge-transfer processes, and transport are discussed in the context of SOFC membrane-electrode assembly modeling

Advances in reforming and partial oxidation of hydrocarbons for hydrogen production and fuel cell applications

One of the most attractive routes for the production of hydrogen or syngas for use in fuel cell applications is the reforming and partial oxidation of hydrocarbons. The use of hydrocarbons in high temperature fuel cells is achieved through either external or internal reforming. Reforming and partial oxidation catalysis to convert hydrocarbons to hydrogen rich syngas plays an important role in fuel processing technology. The current research in the area of reforming and partial oxidation of methane, methanol and ethanol includes catalysts for reforming and oxidation, methods of catalyst synthesis, and the effective utilization of fuel for both external and internal reforming processes. In this paper the recent progress in these areas of research is reviewed along with the reforming of liquid hydrocarbons, from this an overview of the current best performing catalysts for the reforming and partial oxidizing of hydrocarbons for hydrogen production is summarized

The effect of H₂S on internal dry reforming in biogas fuelled solid oxide fuel cells

Internal dry reforming of methane is envisaged as a possibility to reduce on capital and operation costs of biogas fuelled solid oxide fuel cells (SOFCs) system by using the CO2 present in the biogas. Due to envisaged internal dry reforming, the requirement for biogas upgrading becomes obsolete, thereby simplifying the system complexity and increasing its technology readiness level. However, impurities prevailing in biogas such as H2S have been reported in literature as one of the parameters which affect the internal reforming process in SOFCs. This research has been carried out to investigate the effects of H2S on internal dry reforming of methane on nickel-scandia-stabilised zirconia (Ni-ScSZ) electrolyte supported SOFCs. Results showed that at 800°C and a CH4:CO2 ratio of 2:3, H2S at concentrations as low as 0.125 ppm affects both the catalytic and electric performance of a SOFC. At 0.125 ppm H2S concentration, the CH4 reforming process is affected and it is reduced from over 95% to below 10% in 10 h. Therefore, future biogas SOFC cost reduction seems to become a trade-off between biogas upgrading for CO2 removal and biogas cleaning of impurities to facilitate efficient internal dry reforming

Developing carbon tolerant Ni/ScCeSZ cells via aqueous tape casting for direct biogas fed solid oxide fuel cells (SOFC)

Solid Oxide Fuel cell (SOFC) is a promising solution to energy independence, greener energy, with high electrical efficiency and theoretically compatible to operate with gaseous carbonaceous fuel. The problem arises when the benchmark materials (Ni/YSZ) performance drop with operation with carbon fuels. Hence, this thesis aims to develop SOFC cell with alternative materials that have high electrochemical performance with dry carbon fuels for intermediate temperature SOFC. This thesis demonstrates the successful manufacturing of the anode supported cells of Ni/YSZ, Ni/ScCeSZ and Sn-Ni/ScCeSZ via reverse aqueous tape casting method. With this method, SOFC half cells with dense thin electrolyte and porous thick anode produced using multi-layered tape casting and single co-sintering stage. Ni/ScCeSZ was chosen as the base anode substrate material due to the 10ScCeSZ’s high conductivity property and better ability to tolerate carbon-based fuels. Despite the long history of Ni/ScCeSZ cell, this thesis shows the first work that compare Ni/YSZ and Ni/ScCeSZ cells for IT-SOFC with hydrogen and dry carbon fuels. Tin (Sn) introduced as dopant in the final stage to further enhanced the performance in dry carbon operation. for Sn-Ni/ScCeSZ cell. To author’s knowledge, this thesis reported the first work on the electrochemical performance in dry biogas. Comparative study of the electrochemical performance in hydrogen and dry biogas reveals that the maximum power density of Ni/YSZ cell instantly dropped by an average of 80.6% when switched from hydrogen to biogas, 0.37 W/cm$^2$ to 0.05W/cm$^2$, respectively. Ni/ScCeSZ showed better performance in both fuels, with maximum power densities of 0.42 W/cm$^2$ in hydrogen and 0.28 W/cm$^2$ biogas (37.5 % drop). Ni/YSZ and Ni/ScCeSZ show significant differences in the ASR value in biogas operation with values of 2.52 Ω.cm$^2$ and 0.72 Ω.cm$^2$ respectively. With Sn-Ni/ScCeSZ, the OCV increased with the fuel swap from 0.99 V to 1.04 V and the performance in biogas lowered only by an average of 8.3% with a maximum power density of 0.314 W/cm$^2$ in biogas. Contradict to the literature, this thesis provides a new insight to the cause of performances drop with the fuel switch which was mainly affected by the reforming ability of Ni/ScCeSZ and Ni/YSZ anode. Small amount of amorphous carbon deposited on the Ni/YSZ anode while higher amount of graphitic carbon found on the Ni/ScCeSZ and Sn-NiScCeSZ anodes. Sn increased the catalytic activity reforming and methane cracking accompanied by increase amount of graphitic carbon on the anode

Development of Intermediate-Temperature Solid Oxide Fuel Cells for Direct Utilization of Hydrocarbon Fuels

In this study, we compare the performance of 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 H2 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

Micro-structured hollow fibers for micro-tubular solid oxide fuel cells

Micro-tubular solid oxide fuel cells (MT-SOFCs) have received increasing research interest in the past decade. However, current development is restricted in R&D phase due to several technical challenges, such as expensive manufacturing route, which limits mass-scale production, and the difficulties in efficient current collection, especially from the small lumen of micro-tubes. In terms of fabrication, conventional routes usually consist of repetitions of coating and sintering, which is both time and cost-consuming. To tackle this problem, a phase inversion-assisted co-extrusion process has been established in this study, which dramatically simplifies the fabrication process, with improved adhesion. The phase inversion process could lead to the formation of an asymmetric structure, comprising micro-channels and a sponge-like structure. The former morphology could facilitate fuel transport, while the latter provides reactive sites for electrochemical reactions. The feasibility of the new manufacturing route has been established by fabricating anode/anode functional layer (AFL)/electrolyte triple-layer hollow fibers and the results suggest that inserting an AFL could effectively improve power density by 30% due to enlarged triple-phase boundary. As for the current collection from the lumen side, a new nickel-based current collector has been developed via co-extrusion. By controlling the fabrication parameters, a deliberate mesh-structure has been obtained with uniformly distributed entrances. Inserting this nickel-based inner layer considerably increases the electrical conductivity of anode and reduces gas diffusion resistance. After a complete cell was constructed, systematic electrochemical performance tests were undertaken. It has been illustrated that more uniform current collection has been achieved and contact loss, which is the major contributor towards ohmic loss in conventional current collectors, has been significantly reduced to less than 10% of total ohmic loss. This result indeed highlights the features of process economy and high efficiency of the new current collection design and suggests this design to be suitable for large-scale stack construction.Open Acces