• Energy Research

The proton uptake mechanism in a triple conducting oxide, PrBa0.5Sr0.5Co1.5Fe0.5O5+δ, is comprehensively investigated based on defect chemistry and experimental analyses of mass and conductivity changes under dry and humidified atmospheres.

In spite of various advantages of protonic ceramic fuel cells over conventional fuel cells, distinct scepticism currently remains about their applicability because of lower-than-predicted performance and difficulty with scale-up. These challenges mainly stem from the refractory nature of proton-conducting ceramic electrolytes and the low chemical stability of these materials during the sintering process. Here, we present the fabrication of a physically thin, structurally dense and chemically homogeneous electrolyte, BaCe0.55Zr0.3Y0.15O3-δ (BCZY3), through a facile anode-assisted densification of the electrolyte on a structurally and compositionally uniform anode support, which resulted in breakthroughs in performance and scalability. A BCZY3-based protonic ceramic fuel cell with a size of 5 × 5 cm2 exhibits an area-specific ohmic resistance of 0.09 Ω cm2 and delivers a power as high as 20.8 W per single cell at 600 °C. Protonic ceramic fuel cells (PCFCs) operate at lower temperatures than solid oxide fuel cells but suffer from lower performances, especially during scale-up. Here, the authors report a 25 cm2 PCFC based on a BaCe0.55Zr0.3Y0.15O3–δ electrolyte that displays a record-high power density of 20.8 W at 600 °C.

Abstract Fuel flexibility, which is one of the most important advantages of the solid oxide fuel cell, can be compromised at lower operating temperatures. Thus in this study, normal butane is selected as the fuel and multiscale-architectured thin-film-based solid oxide fuel cells are operated in direct butane utilization mode at T = 600 °C. Palladium (Pd) is chosen as the secondary catalyst to assist the reforming of the butane and is inserted at different positions at the anode. By combining two different Pd insertion methods, sputtering and infiltration, four different thin-film-based solid oxide fuel cells were prepared: (1) the cell without Pd (Ref-cell); (2) the cell with Pd at the anode functional layer, which was fabricated by alternating sputtered Pd layers with pulsed-laser deposited NiO/yttria-stabilized zirconia layers (Pd-S-cell); (3) the cell with Pd at the anode support, which was fabricated by infiltration (Ref-I-cell); and (4) the cell with Pd at both the anode functional layer and anode support (Pd-S-I-cell). As expected, different Pd distributions were observed along the thickness of the anode. The Pd-S-I-cell showed significant enhancement in performance and durability. Approximately three times cell performance enhancement for the best case is observed in comparison with that of the Ref-cell. The Pd distribution, not only at the anode functional layer but also at the anode support, appears to have accelerated the electrochemical and thermochemical reactions. In addition, a lesser degree of carbon deposition was observed at the anode of the Pd-S-I-cell as compared with the case of the others.

Degradation of oxygen electrode in reversible solid oxide cells operating in both electrolysis and fuel-cell modes is a critical issue that should be tackled. However, origins and mechanisms thereof have been diversely suggested mainly due to the difficulty in precise analysis of microstructural/compositional changes of porous electrode, which is a typical form in solid oxide cells. In this study, we investigate the degradation phenomena of oxygen electrode under electrolysis and fuel-cell long-term operations for 540 h, respectively, using a geometrically well-defined, nanoscale La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) dense film with a thickness of ∼70 nm. Based on assessments of electrochemical properties and analyses of microstructural and compositional changes after long-term operations, we suggest consolidated degradation mechanisms of oxygen electrode, including the phenomena of kinetic demixing/decomposition of LSCF, which is not readily observable in the typical porous-structured electrode.

Single-atom Pt/ceria catalysts are extremely active and thermally stable at over 700 °C in high-temperature solid oxide cell electrodes.

Over the past several years, important strides have been made in demonstrating protonic ceramic fuel cells (PCFCs). Such fuel cells offer the potential of environmentally sustainable and cost-effective electric power generation. However, their power outputs have lagged behind predictions based on their high electrolyte conductivities. Here we overcome PCFC performance and stability challenges by employing a high-activity cathode, PrBa_(0.5)Sr_(0.5)Co_(1.5)Fe_(0.5)O_(5+δ) (PBSCF), in combination with a chemically stable electrolyte, BaZr_(0.4)Ce_(0.4)Y_(0.1)Yb_(0.1)O_3 (BZCYYb4411). We deposit a thin dense interlayer film of the cathode material onto the electrolyte surface to mitigate contact resistance, an approach which is made possible by the proton permeability of PBSCF. The peak power densities of the resulting fuel cells exceed 500 mW cm^(−2) at 500 °C, while also offering exceptional, long-term stability under CO_2.