Anodes for Carbon-Fueled Solid Oxide Fuel Cells

A new strategy for improving the electrochemical performance of perovskite cathodes: pre-calcining the perovskite oxide precursor in a nitrogen atmosphere

Increasing the concentration of oxygen deficiency in perovskite oxides by suitable cation doping or anion doping can significantly increase the cathode ionic conductivity, thus improving the oxygen reduction reaction activity in solid oxide fuel cells (SOFCs). Herein, pre-calcining the perovskite oxide precursor in N2 atmosphere is a new strategy to further improve the oxygen non-stoichiometry (δ) and electrocatalytic activity of the cathode. The obtained nitrogen-treated Sm0.5Sr0.5CoO3-δ (SSC) powder has higher oxygen non-stoichiometry than the untreated one. The δ value is 0.27 for SSC-400 at 800 °C in air. The obtained nitrogen-treated SSC-400 cathodes calcined at 1000 °C show improved electrochemical performance compared to SSC-air, achieving the polarization resistance (R p) values to be 0.035, 0.078 and 0.214 Ω cm2 at 700 °C, 650 °C and 600 °C. The maximum power density of the cell with the SSC-600 cathode reaches 0.87, 1.16 and 1.24 W cm-2 at 600, 650 and 700 °C, which are more excellent than SSC-air. Pre-calcining the perovskite oxide precursor in N2 at a suitable temperature can remarkably improve the electrochemical capability of the cathode and provide a convenient and useful strategy to alleviate the problem of oxygen deficiency in perovskite oxides.

Honeycombed Porous, Size-Matching Architecture for High-Performance Hybrid Direct Carbon Fuel Cell Anode

Direct carbon fuel cells (DCFCs) demonstrate both superior electrical efficiency and fuel utilization compared to all other types of fuel cells, and it will be the most promising carbon utilization technology if the sluggish anode reaction kinetics that derives from the use of solid fuel can be addressed. Herein, the electrode morphology and fuel particle size are comprehensively considered to fabricate an efficient DCFC anode skeleton. A honeycombed and size-matching anode architecture with dual-scale porous structure is developed by water droplet templating, which demonstrates an efficient strategy to address the challenge of poor carbon reactivity and improve the electrochemical performance of DCFCs. Single cell with this designed anode framework demonstrates excellent performance, and the maximum power density is as high as 765 mW cm^-2 at 800 °C when using the matching carbon fuel. The size-matching between carbon fuel and anode framework shows a remarkable effect on the improvement of mass-transfer processes at the anodes. The significant contribution of the difficult electrochemical oxidation of carbon to the output performance is also demonstrated. These results represent a promising structural design strategy in developing high-performing fuel cells.

Ni stabilized rock-salt structured CoO; Co1-x Ni x O: tuning of eg electrons to develop a novel OER catalyst

The oxygen evolution reaction (OER) is a key half-reaction in hydrogen–oxygen electrolysers that is very important for efficient electrochemical energy generation, storage and fuel production that offers a clean alternative to fissile fuel combustion based energy systems. Several transition metal containing perovskites were recently explored for the development of superior OER catalysts, and their activity was correlated with the applied potentials at a specific current density to e_g electron density present in the materials. The rock salt structure is envisaged here as a model host structure similar to perovskite to tune the e_g electrons to obtain superior electro-catalytic activity. Incorporation of Ni into CoO lattices helps to stabilize the rock salt structure and modulate the e_g electrons to develop superior OER and ORR electrocatalysts. Nickel doped rock salt structured CoO, Ni_xCo_1−xO (0 ≤ x ≤ 0.5), were synthesized by employing a solid state metathesis synthesis route. The compounds were characterised by powder X-ray diffraction (XRD), TGA, FT-IR and X-ray Photoelectron Spectroscopy (XPS). Ni_0.3Co_0.7O with 1.3 e_g electrons showed superior electrocatalytic activity for the oxygen evolution reaction. The overpotential for the Ni_0.3Co_0.7O sample was also found to be ∼0.450 V for 1 M and about ∼0.389 V at 5 M concentration of the KOH electrolyte.

Incorporation of Ni into CoO lattices helps to stabilize the rock salt structure and modulate the e_g electrons to develop superior OER and ORR electrocatalysts.

Enhanced Stability and Catalytic Activity on Layered Perovskite Anode for High-Performance Hybrid Direct Carbon Fuel Cells

In this work, we investigate a novel A-site ordered layered perovskite oxide, (PrBa)_0.95Fe_1.8-xCu_xNb_0.2O_5+δ (PBFCN), as an anode material for hybrid direct carbon fuel cells (HDCFCs). We study the effect of anode composition on the electrochemical performance of HDCFCs. The electrolyte-supported single cell with (PrBa)_0.95Fe_1.4Cu_0.4Nb_0.2O_5+δ (PBFCu_0.4N) anode achieves the highest peak power density of 431 mW cm^-2 at 800 °C with activated carbon as the fuel. Moreover, a power generation unit is also made to demonstrate the practical utilization of PBFCN, which delivers a peak power of 0.51 W at 800 °C without any carrier gas, and a small fan can operate for more than 10 h by using the as-fabricated HDCFC as a power generation unit. The PBFCN anode achieves greatly enhanced catalytic activity by improving the chemical adsorption and electrochemical oxidation of CO at the anode/CO interface, which is mainly due to the high-activity Cu ions in PBFCN. The inactive element Nb doping and ordered layered structure endow the material with excellent redox structural stability. The present study provides a new idea for the design and development of high-performance anode materials for HDCFCs applications.

Two orders of magnitude enhancement in oxygen evolution reactivity on amorphous Ba0.5Sr0.5Co0.8Fe0.2O3-δ nanofilms with tunable oxidation state

Perovskite oxides exhibit potential for use as electrocatalysts in the oxygen evolution reaction (OER). However, their low specific surface area is the main obstacle to realizing a high mass-specific activity that is required to be competitive against the state-of-the-art precious metal-based catalysts. We report the enhanced performance of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) for the OER with intrinsic activity that is significantly higher than that of the benchmark IrO₂, and this result was achieved via fabrication of an amorphous BSCF nanofilm on a surface-oxidized nickel substrate by magnetron sputtering. The surface nickel oxide layer of the Ni substrate and the thickness of the BSCF film were further used to tune the intrinsic OER activity and stability of the BSCF catalyst by optimizing the electronic configuration of the transition metal cations in BSCF via the interaction between the nanofilm and the surface nickel oxide, which enables up to 315-fold enhanced mass-specific activity compared to the crystalline BSCF bulk phase. Moreover, the amorphous BSCF-Ni foam anode coupled with the Pt-Ni foam cathode demonstrated an attractive small overpotential of 0.34 V at 10 mA cm^-2 for water electrolysis, with a BSCF loading as low as 154.8 μg cm^-2.

Challenges in developing direct carbon fuel cells

A direct carbon fuel cell (DCFC) can produce electricity with both superior electrical efficiency and fuel utilisation compared to all other types of fuel cells.