Low Temperature PEM vs. High Temperature PEM fuel cells

Transcription

1 Hochschule Ulm presentation seminar EPS (ECPS2) Low Temperature PEM vs. High Temperature PEM fuel cells Aaron Fesseler EE Tim Kistenfeger EE supervisor: Dr. Joachim Scholta WS 2017/

2 Table of contents 1. Introduction 2. Fundamentals 3. Classification of PEM fuel cells 4. Electrolytes of LT-PEMFC and HT-PEMFC 5. Applications of LT-PEMFC and HT-PEMFC 6. Advantages and disadvantages 7. Conclusion 2

3 1. Introduction Introduction PEM fuel cell (PEMFC): special type of fuel cell called Proton Exchange Membrane Fuel Cell also known as Polymer Electrolyte Membrane Fuel Cells available as low temperature and high temperature types differences in function [1,2] 3

4 1. 2. Fundamentals Fundamentals Fuel cell: electrochemical cell, which directly converts the chemical energy from a fuel into electricity electrochemical reaction of hydrogen fuel with oxygen or another oxidizing substance continuous supply of the substances from external sources [1,3] 4

5 1. 2. Fundamentals Fundamentals PEM: Polymer Electrolyte Membrane is also known as Proton Exchange Membrane based by a semipermeable membrane designed for conducting protons while it works as: electronic insulator reactant barrier Anode: Hydrogen (H 2 ) Cathode: Oxygen (O 2 ) water formation (H 2 0) Release of electrons current flow 5 [1]

6 1. 2. Fundamentals Fundamentals Chemical reactions: anode reaction (oxidation): cathode reaction (reduction): total reaction (redox-reaction): energy Anode: Hydrogen (H 2 ) Cathode: Oxygen (O 2 ) water formation (H 2 0) Release of electrons current flow 6 [1,4, 5]

7 1. 2. Fundamentals Fundamentals Cell efficiency: basical: η = dependent of carnotefficiency maximum efficiency is bounded by Gibbs free enthalpy und the lower heating value decreasing efficiency with higher temperatures, molar efficiency increases 7 [5]

8 Classificaton of PEM fuel cells Classification of PEM fuel cells Classification of fuelled-systems: direct-fuelled system: readily electrochemically oxidation and direct fed-in into the fuel cell indirect-fuelled system: converting of the fuel in a so called fuelprocessing subsystem convertition to an easily oxydisable hydrogen-rich gas to fed into the fuel cell general classification on operation area of temperture 8 [4,5]

9 Classificaton of PEM fuel cells Classification of PEM fuel cells Cell-type name name electrolyte / membrane temperature range gas efficiency power range Low temperature PEMFC (LT-PEMFC) LT-PEMFC polymer electrolyte membrane fuel cell PEM Nafion 0 80 C hydrogen (H 2 ) methane (CH 4 ) methanol (CH 3 OH) 60 % with H 2 40 % with CH 4 up to 100 kw High temperature PEMFC (HT-PEMFC) HT-PEMFC high temperture polymer electrolyte membrane fuel cell speek concentrated phosphoric acid (H 3 PO 4 ) C hydrogen (H 2 ) methane (CH 4 ) 40 % up to 1 MW 9 [4,5]

10 Electrolytes of LT-PEMFC and HT-PEMFC Electrolytes of LT-PEMFC and HT-PEMFC Nafion modification of teflon forms an entirely new group of polymers characteristics: high chemical resistance fast diffusion of water and alcohols, but hydraulically tight selectively conductive for protons and other cations (blocking effect for anions) operating temperatures compared to other polymers (up to 120 C) recommended for LT-PEMFC 10 [6,7]

11 Electrolytes of LT-PEMFC and HT-PEMFC Electrolytes of LT-PEMFC and HT-PEMFC speek covalently bound macromolecules/components no leaching out Reduced swelling (stiff backbone) Good protonic conductivity degradation process begins first above 580 C (main chain decomposition) recommended for HT-PEMFC 11 [5]

12 Electrolytes of LT-PEMFC and HT-PEMFC Electrolytes of LT-PEMFC and HT-PEMFC concentrated phosphoric acid (H 3 PO 4 ) normal or ortho-phosphoric acid is the most important acid of phosphorus anhydrous substance is highly hygroscopic tri-proton acid and reacts with respect to the first deprotonation as a medium-strength acid corrosive acid recommended for HT-PEMFC 12 [8,9]

13 Applications of LT-PEMFC and HT-PEMFC Applications of LT-PEMFC and HT-PEMFC LT-PEMFC: lower power range small stationary und mainly mobile / portable applications heating and current supply (home), consumer products (notebook, ) E-mobility (cars, planes, ) 13 [10,11]

14 Applications of LT-PEMFC and HT-PEMFC Applications of LT-PEMFC and HT-PEMFC HT-PEM: higher power range huge stationary applications power plants 14 [12]

15 Advantages and disadvantages 7. 6.) Advantages and disadvantages Cell-type advantages disadvantages LT-PEMFC lower operating temperatures from 0 80 C general high current density, also below 80 C slower material degradation HT-PEMFC higher operating temperatures from C only small coolers required high waste heat can be used for other things nearly no influnences of COcontent tolerances faster kinetics of electrochemical reactions out of the higher temperature range (noble metal load is more reduced) low CO content (< 20 ppm) is problematic huge coolers required water management system is required pre-heating of the system is required additional power source for generating the heat long reaction time (heat-time) only limited selection of materials, which are additionally expensive general lower current density faster material degradation 15 [1,4,5]

16 Conclusion 7.) Conclusion Low Temperature PEMFC: especially used for mobile applications optimally for use with hydrogen (best efficiency) higher current density fast response High Temperature PEMFC: especially used for stationary applications lower influence on CO-tolerances fuel processing and water management are easier [1,4,5,11,13] 16

17 Thank you for your attention!

18 Sources: [1] [2] [3] [4] Vorlesungsunterlagen ECPS1 (ZSW) [5] Vorlesungsunterlagen ECPS2 (ZSW) [6] [7] [8] [9] [10] toffzellen/h_tec/brennstoffzellen_funktion_anwendung/brennstoffzellen_funktion_anwendung.vlu/page/ vsc/de/ch/16/pc/elektrochemie/brennstoffzellen/h_tec/brennstoffzellen_funktion_anwendung/brennsto ffzelle_anwendung_allgemein.vscml.html [11] stoffzellen_funktion_anwendung/brennstoffzellen_funktion_anwendung.vlu/page/vsc/de/ch/16/pc/elekt rochemie/brennstoffzellen/h_tec/brennstoffzellen_funktion_anwendung/brennstoffzelle_anwendung_m obil.vscml.html [12] stoffzellentypen/brennstoffzellentypen.vlu/page/vsc/de/ch/16/pc/elektrochemie/brennstoffzellen/h_tec/ brennstoffzellentypen/phosphorsaeure_brennstoffzelle.vscml.html [13]