Effects of Ammonia Impurities on the Hydrogen Flow in High and Low Temperature Polymer Electrolyte Fuel Cells

Abstract

Fuel cells are a promising technology to use as a source of electricity and heat for buildings, and as an electrical power source for electric motors propelling vehicles. They consume hydrogen as fuel and oxygen to produce electricity, heat and water. Conventional fuels, such as natural gas, methanol, or even gasoline are reformed to produce the hydrogen required by the fuel cells. During the reforming process, impurities are inevitably obtained in the hydrogen flow. One of them is ammonia (NH 3 ) that can result in serious damage to the fuel cell operation. In this paper, the effects produced by different concentrations of NH 3 present in the hydrogen flow on the membrane electrode assembly (MEA) performance are studied, differentiating between irreversible and recoverable damages. Strictly experimental, the study includes both low and high temperature polymer electrolyte fuel cells (PEFC).The NH 3 poisoning effect is analyzed and quantified by comparing the polarization curves. After the poisoning stage, the cells are subjected to a regeneration process (feeding the cell with neat H 2 ) with the aim of knowing the membrane's recovery capacity. The experimental results demonstrate that in low temperature (LT)-PEFCs, the cell recovers its performance almost completely with a new exposure to neat H 2 , in spite of the damage previously caused by the presence of traces of NH 3 in the anode feed stream. In contrast, in high temperature (HT)-PEFCs, the cell suffers irreversible damage, even with short time exposure to NH 3 . The paper concludes with discussing the possible chemical interactions by which NH 3 affects the cell performance.

Performance Characteristics of a Direct Ammonia Fuel Cell with an Anion Exchange Membrane

“…If conventional Pt is used as the cathode catalyst, the intermediate product of ammonia oxidation at the cathode, N*, will lead to the toxic deactivation of the cathode catalyst Pt, thus affecting the performance of the ammonia fuel cell. 45 In contrast, according to previous studies, Pd is insensitive to adsorbed N produced during ammonia oxidation at the cathode and has some resistance to poisoning. 46 Following these considerations, Pd is chosen as the cathode catalyst.…”

“…During the fuel cell operations, ammonia from the anode would inevitably diffuse across the membrane to the cathode catalyst layer and then be oxidized. If conventional Pt is used as the cathode catalyst, the intermediate product of ammonia oxidation at the cathode, N*, will lead to the toxic deactivation of the cathode catalyst Pt, thus affecting the performance of the ammonia fuel cell . In contrast, according to previous studies, Pd is insensitive to adsorbed N produced during ammonia oxidation at the cathode and has some resistance to poisoning .…”

Influence of Ammonia Contamination on HT-PEM Fuel Cell Platinum Catalyst

“…Llerena et al recently performed LT-and HT-PEMFC tests in presence of NH 3contaminated hydrogen and showed a strong negative impact on both cell performances. Cell recovery by use of neat hydrogen was successful in case of the low temperature type but not successful in case of the high temperature type (26).…”

“…In this view HT-PEM fuel cell degradation provoked by ammonia needs much better understanding. Moreover, even low NH 3 concentrations were shown to significantly impact the HT-PEMFC (26)(27). This study therefore focuses on the electrochemical investigation of the HT-PEMFC single cell on one hand and on the platinum catalyst on other hand.…”

2023 roadmap on ammonia as a carbon-free fuel

“…It is well established that ammonia is not a suitable fuel for PEMFCs as it will degrade the acidic membranes used as the electrolyte [106]. Indeed the presence of just a few ppm of NH 3 in either the oxidant or fuel streams can cause a considerable loss in performance after only a short exposure time [107][108][109][110][111][112][113]. NH 3 could be used indirectly in PEMFCs but additional technologies would be required to produce H 2 of a suitably very high purity [99].…”