Biogas as a fuel for solid oxide fuel cells and synthesis gas production: effects of ceria-doping and hydrogen sulfide on the performance of nickel-based anode materials

Abstract

Numerous investigations have been carried out into the conversion of biogas into synthesis gas (a mixture of H(2) + CO) over Ni/YSZ anode cermet catalysts. Biogas is a variable mixture of gases consisting predominantly of methane and carbon dioxide (usually in a 2 : 1 ratio, but variable with source), with other constituents including sulfur-containing gases such as hydrogen sulfide, which can cause sulfur poisoning of nickel catalysts. The effect of temperature on carbon deposition and sulfur poisoning of 90 : 10 mol% Ni/YSZ under biogas conversion conditions has been investigated by carrying out a series of catalytic reactions of methane-rich (2 : 1) CH(4)/CO(2) mixtures in the absence and presence of H(2)S over the temperature range 750-1000 °C. The effect of ceria-doping on carbon dioxide reforming, carbon deposition and sulfur tolerance has also been investigated by carrying out a similar series of reactions over ceria-doped Ni/YSZ. Ceria was doped at 5 mol% of the nickel content to give an anode catalyst composition of 85.5 : 4.5 : 10 mol% Ni/CeO(2)/YSZ. Reactions were followed using quadrupolar mass spectrometry (QMS) and the amount of carbon deposition was analysed by subjecting the reacted catalyst samples to a post-reaction temperature programmed oxidation (TPO). On undoped Ni/YSZ, carbon deposition occurred predominantly through thermal decomposition of methane. Ceria-doping significantly suppressed methane decomposition and at high temperatures simultaneously promoted the reverse Boudouard reaction, significantly lowering carbon deposition. Sulfur poisoning of Ni/YSZ occurred in two phases, the first of which caused the most activity loss and was accelerated on increasing the reaction temperature, while the second phase had greater stability and became more favourable with increasing reaction temperature. Adding H(2)S significantly inhibited methane decomposition, resulting in much less carbon deposition. Ceria-doping significantly increased the sulfur tolerance of Ni/YSZ, however, in the presence of H(2)S ceria did not promote the reverse Boudouard reaction and at high temperatures carbon deposition was greater over ceria-doped Ni/YSZ. In order to further study the effects of ceria-doping, a solid oxide fuel cell (SOFC) was constructed with a ceria-doped anode cermet and its electrical performance on simulated biogas compared to hydrogen was tested. This fuel cell was subsequently ran for 1000 h on simulated biogas with no degradation in its overall electrical performance.

Biogas Catalytic Reforming Studies on Nickel‐Based Solid Oxide Fuel Cell Anodes

“…Furthermore, it has been shown that modifying nickelbased anodes with precious metals or oxides such as ceria and doped ceria improved catalytic performance and sulfur tolerance of SOFC anodes [7,27,[39][40][41][42][43]. In the present work, the effect of modifying the anode with palladium/gadoliniumdoped ceria (Pd-CGO) was studied.…”

“…These observed differences might suggest that the presence of Pd-CGO influences the sulfur retention ability of the catalyst, especially under steam reforming conditions. Ceria is a known sulfur sorbent and has been reported to improve the sulfur tolerance of Ni/YSZ anodes [7,39,59]. In addition, Sm-doped ceria has been reported to act as a sulfur sorbent in an SOFC operated with sulfur containing hydrogen fuel.…”

“…Biogas which typically contains little or no higher hydrocarbons, can be applied directly as fuel in SOFC anodes. In recent years, there has been an increasing amount of literature reports on biogas-fueled SOFCs [7][8][9][10][11][12][13][14][15].…”

SOFC fuelled with reformed urea

“…Among the different fuels that have been studied in high temperature fuel cells, it is worth mentioning ammonia [1][2][3][4][5], biogas [6][7][8][9][10][11][12][13][14], syngas from biomass gasification [15][16][17][18], hydrogen rich mixtures of gases [7], CO rich fuels [19][20][21][22]. Even though the performance with those unconventional fuels has always been high, http://dx.doi.org/10.1016/j.apenergy.2015.04.126 0306-2619/Ó 2015 Elsevier Ltd. All rights reserved.…”

Oxidative Dry‐Reforming of Biogas: Reactor Design and SOFC System Integration

“…[18] The use of synthetic or real biogas in SOFCs has not only been modeled in numerous publications, [19][20][21][22][23][24][25] but has also been investigated in experimental studies. [26][27][28][29][30][31][32][33][34][35][36][37] Most research work has been done with internal reforming systems. If the experiments are not performed in furnaces, internal reforming can suffer from two disadvantages: high temperature gradients over the cell and the risk of carbon formation.…”