Highly efficient, coking-resistant SOFCs for energy conversion using biogas fuels

Abstract

Solid oxide fuel cells (SOFCs) afford an opportunity for the direct electrochemical conversion of biogas with high efficiency; however, direct utilisation of biogas in nickel-based SOFCs is a challenge as it is subject to carbon deposition. A biogas composition representative of a real operating system of 36% CH 4 , 36% CO 2 , 20% H 2 O, 4% H 2 and 4% CO used here was derived from an anode recirculation method. A BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3Àd (BCZYYb) infiltrated Ni-YSZ anode was investigated for biogas conversion. The infiltration of BCZYYb significantly promoted the electrochemical reactions and the cells exhibited high power output at the operational temperatures of 850, 800 and 750 C. At 800 C, supplied with a 20 ml min À1 biogas, the cell with a BCZYYb-Ni-YSZ anode, generated 1.69 A cm À2 at 0.8 V with an optimal amount of 0.6 wt% BCZYYb, whereas only 0.65 A cm À2 was produced with a non-infiltrated Ni-YSZ in the same conditions. At 750 C, a maximum power density of 1.43 W cm À2 was achieved on a cell with a BCZYYb-Ni-YSZ anode, a 3 mm dense YSZ film electrolyte, a Gd 0.1 Ce 0.9 O 2 (GDC) buffer layer and a La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 -Gd 0.1 Ce 0.9 O 2 (LSCF-GDC) composite cathode. The cell remained stable, while operating at 0.8 V for 50 hours with a current density of 1.25 A cm À2 . A well-designed cell structure and selected components made it possible to obtain excellent performance at good fuel utilisation. The analysis of gases in open-circuit conditions or under various current loads suggested that the prevalent reaction was reforming of methane without coking. This study demonstrates that the BCZYYb-Ni-YSZ is a promising electrode for carbon-containing fuel.Depending on the reaction conditions, the equilibrium for the water-gas shi can be pushed in either direction. In fuel cell systems, the dominant reactions will be dependent on the gas 133 4463808; Tel: +44 (0) 133 4463817 † Electronic supplementary information (ESI) available. See

Biogas Management: Advanced Utilization for Production of Renewable Energy and Added-value Chemicals

“…In regard to this, fast O 2− -ionic conduction in the solid electrolyte at the required cell operating temperature is the key factor-rather than the kinetics of the anodic chemical and electrochemical reactions; the latter appear to be fast at temperatures > ∼600 • C. iv. Electrical power output characteristics of direct biogas FCs were found to compare favorably with those obtained with the same cell under H 2 feed (Fuerte et al, 2014;Ma et al, 2015). This probably implies that reaction (R22) dominates cell performance.…”

“…This concept, also called direct-biogas solid oxide fuel cell (DB-SOFC), offers several advantages in comparison to the previously discussed method of external reforming (Figure 5), has currently received much attention in both experimental (Goula et al, 2006;Yentekakis, 2006 FIGURE 5 | Schematic of the differences between external (A) and internal (B) reforming concepts for SOFC-added electrical power generation from biogas. Papadam et al, 2012;Takahashi et al, 2012;Lanzini et al, 2013;Ma et al, 2015; and references therein) and modeling studies (Lanzini et al, 2011;Ni, 2013;Janardhanan, 2015a,b). Most of these studies made use of Ni-based cermet anodes, doped with additives in some cases in order to prevent carbon deposition (e.g., Yentekakis, 2006;Ma et al, 2015;Niakolas et al, 2015).…”

“…Papadam et al, 2012;Takahashi et al, 2012;Lanzini et al, 2013;Ma et al, 2015; and references therein) and modeling studies (Lanzini et al, 2011;Ni, 2013;Janardhanan, 2015a,b). Most of these studies made use of Ni-based cermet anodes, doped with additives in some cases in order to prevent carbon deposition (e.g., Yentekakis, 2006;Ma et al, 2015;Niakolas et al, 2015). Table 3 summarizes some direct biogas fuel cells studies that are worthy of particular note.…”

“…With this aim, anode-or cathode-supported fuel cell designs with very thin solid electrolytes (ca. 3-20 µm) were successfully applied, delivering as expected superior power generation (Wang et al, 2011a;Takahashi et al, 2012;Ma et al, 2015). Further development of anodic materials together with advanced fuel cell designs that minimize cell overpotentials (of which there is much expertise in solid oxide fuel cell technology) in combination with optimal operational conditions (information provided by direct biogas fuel cell modeling studies) are expected to lead to the development of highly efficient and cost-effective direct biogas fuel cells in the near future.…”

Failure Modes, Mechanisms, Effects, and Criticality Analysis of Ceramic Anodes of Solid Oxide Fuel Cells

“…In order to prevent carbon deposition, either steam reformation or dry reformation (using CO 2 ) is used, causing water-gas shift reactions (such as CO + H 2 O − > CO 2 + H 2 ) and thereby converting the carbon into CO or CO 2 and preventing its deposition. However, the addition of CO 2 or steam along with the fuel decreases the fuel concentration and in turn significantly reduces fuel utilization as well as the electrical performance of the cell [62,63]. These mechanisms mainly apply to Ni catalysts; whereas, the impact on other catalyst needs to be studied.…”