Operating Behavior and Scale-Up of an ECPrOx Unit for CO Removal from Reformate for PEM Fuel Cell Application

Abstract

Recently, an approach involving electrochemical preferential oxidation (ECPrOx) of CO was suggested as having the potential to replace the PrOx concept for deep CO removal from reformate gas in proton exchange membrane (PEM) fuel cells. The first part of this paper deals with the characterization of such an ECPrOx unit from a reaction engineering point of view. Based on a spatially lumped, isothermal model, the qualitative selectivity-conversion behavior is discussed for varying feed flow rates and CO inlet mole fractions. A simple two-phase mechanism is suggested that explains the findings. The second part of the contribution considers qualitative questions on cascading of two ECPrOx reactors. The crucial importance of the configuration of their electrical connection is demonstrated and explained. While two cells connected electrically in parallel exhibit almost the same selectivity-conversion behavior in comparison with a single cell, an electrical series connection enables a considerable increase in the selectivity at the same CO conversion.

Electrochemical Oxidation of Carbon‐Containing Fuels and Their Dynamics in Low‐Temperature Fuel Cells

“…Such a configuration allows independent potential oscillations in each cell. This in turn enables deeper CO removal than two cells connected in parallel, as illustrated in Figure 24 213. In a parallel connection, the upstream cell is unable to oscillate independently and CO conversion is hindered because it is enslaved by its downstream counterpart.…”

“… Time evolution of selected variables: a) anode overvoltage and b) CO outlet mole fraction for the electrical series connection of two ECPrOx reactors; c) anode overvoltage and d) CO outlet mole fraction for electrical parallel connection. Reproduced from reference 213 with permission from the Electrochemical Society. …”

Complex Oscillatory Response of a PEM Fuel Cell Fed with H[sub 2]/CO and Oxygen

“…Besides the cited data of half-cell experiments, there are also several recent papers on the kinetic instabilities in low temperature proton exchange membrane fuel cells ͑PEMFCs͒ fed with H 2 /CO mixtures. [28][29][30][31][32][33][34][35] In most cases, oscillatory kinetics are observed in PEMFCs with a Pt/C cathode fed with oxygen and a PtRu/C anode fed with a H 2 /CO mixture. Besides the fundamental aspects that underlie this complex system, considerably higher average power densities are observed under an oscillatory regime when compared with those observed under a stable steady state.…”

Carbon monoxide poisoning and mitigation strategies for polymer electrolyte membrane fuel cells – A review

“…105 Hanke-Rauschenbach (2009) studied the oscillatory behaviour of potential using the model presented by as a base, and compared the behaviour of two ECPrOx reactors with electrical connections in series and in parallel. 42,142 It was concluded that the CO conversion is improved in the series system due to the independent oscillations of each unit. The units connected in parallel oscillate simultaneously, affecting the performance of the system.…”