The effect of heavy tars (toluene and naphthalene) on the electrochemical performance of an anode-supported SOFC running on bio-syngas

TL;DR

This study investigates how heavy tar compounds like toluene and naphthalene affect the performance of Ni-YSZ anode-supported SOFCs using bio-syngas, revealing significant degradation especially with naphthalene and highlighting the poisoning effect of heavy tars.

Contribution

It provides new insights into the detrimental effects of heavy tar compounds on SOFC performance and elucidates their impact on electrochemical reactions and catalyst poisoning mechanisms.

Findings

Naphthalene causes severe performance degradation in SOFCs.

Heavy tars inhibit water gas shift and CO electro-oxidation.

Heavy tars act as poisons rather than fuels for SOFCs.

Abstract

The effect of heavy tar compounds on the performance of a Ni-YSZ anode supported solid oxide fuel cell was investigated. Both toluene and naphthalene were chosen as model compounds and tested separately with a simulated bio-syngas. Notably, the effect of naphthalene is almost negligible with pure H2 feed to the SOFC, whereas a severe degradation is observed when using a bio-syngas with an H2:CO = 1. The tar compound showed to have a remarkable effect on the inhibition of the WGS shift-reaction, possibly also on the CO direct electro-oxidation at the three-phase-boundary. An interaction through adsorption of naphthalene on nickel catalytic and electrocatalytic active sites is a plausible explanation for observed degradation and strong performance loss. Different sites seem to be involved for H2 and CO electro-oxidation and also with regard to catalytic water gas shift reaction. Finally, heavy tars (C>=10) must be regarded as a poison more than a fuel for SOFC applications, contrarily to lighter compounds such benzene or toluene that can directly reformed within the anode electrode. The presence of naphthalene strongly increases the risk of anode re-oxidation in a syngas stream as CO conversion to H2 is inhibited and also CH4 conversion is blocked.